Highly Sensitive Dopamine Biochemical Sensor Employing Pristine Electrodeposited Reduced Graphene Oxide

Highly Sensitive Dopamine Biochemical Sensor Employing Pristine Electrodeposited Reduced Graphene Oxide | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Highly Sensitive Dopamine Biochemical Sensor Employing Pristine Electrodeposited Reduced Graphene Oxide Muhammad Haziq Ilias, Zainiharyati Mohd Zain, Maizatul Zolkapli, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6704266/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 6 You are reading this latest preprint version Abstract Dopamine is a crucial neurotransmitter, and atypical amounts have been linked to various neurological disorders. Nonetheless, the precise and efficient detection of dopamine is impeded by interference from structurally analogous biomolecules such as uric acid and ascorbic acid. A pristine reduced graphene oxide (RGO) on screen-printed gold electrode (SPGE) has been successfully developed for the sensitive and selective detection of dopamine. Reduced graphene oxide (RGO) was synthesised via the electrodeposition method, with manufacturing conditions optimised by varying the concentration of graphene oxide (GO) and the temperature of the water bath. The ideal conditions were determined to be 500 mgmL⁻1 of GO and 40°C, attributed to the elevated C:O ratio of RGO on SPGE, leading to superior electrochemical performance. The optimised RGO/SPGE sensor was evaluated for dopamine detection via square-wave voltammetry (SWV). The findings suggest a high sensitivity of 446.83 µA mM⁻¹cm⁻², with a detection limit (LOD) of 1.2 µM, demonstrating its ability to identify low quantities of dopamine. FTIR analysis demonstrated a significant reduction of GO and the interaction between dopamine and the RGO-modified surface, corroborating the observed electrochemical changes. Electrochemical impedance spectroscopy (EIS) was employed to examine the interfacial charge transfer characteristics of the electrode at different dopamine concentrations. The reduction in charge transfer barrier with rising dopamine concentrations indicates enhanced electron transfer kinetics. The sensor exhibited significant selectivity for dopamine, distinguishing it from interfering substances such as uric acid (UA) and ascorbic acid (AA). Moreover, the sensor exhibited remarkable stability, retaining 91.75% of its initial current response. The sensor has exceptional reproducibility and repeatability, with RSD values of 4.04% and 3.28% (n = 3), respectively. These findings underscore the optimised RGO/SPGE sensor's promise as a reliable and economical electrochemical sensing platform, particularly in biological matrices. Reduced Graphene Oxide (RGO) Screen-printed Gold Electrode (SPGE) Square Wave Voltammetry (SWV) Electrochemical Impedance Spectroscopy (EIS) Dopamine (DA). Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 1.0 Introduction Dopamine (DA) (3,4-dihydroxyphenethylamine), an important neurotransmitter discovered by Arvid Carlsson in 1957, plays a pivotal role in various physiological and neurological processes. As a member of the biogenic amines class of neurotransmitters, DA facilitates the transmission of sensory signals between neurons via synapses, contributing to normal brain function[ 1 ], [ 2 ]. It influences multiple systems, including the cardiovascular, central nervous, endocrine, and renal systems, while also regulating physiological processes such as attention, learning, memory, movement, mood, behaviour, and mental cognition. Clinically, the accurate detection of dopamine is crucial for diagnosing and managing neurological disorders such as Parkinson’s disease, schizophrenia, depression, and attention deficit hyperactivity disorder (ADHD). An imbalance in dopamine levels in the brain is associated with neurodegenerative diseases, including Alzheimer’s and Parkinson’s, as well as mental health conditions like addiction and schizophrenia[ 3 ], [ 4 ], [ 5 ]. The ability to accurately monitor dopamine levels is critical for diagnosing and managing these conditions. Rapid, non-invasive, and highly sensitive detections methods could significantly improve early diagnosis and therapeutic interventions, offering better prevention. Several analytical techniques, such as chemiluminescence, chromatography, colorimetric assays, fluorescence, and spectrophotometry, have been explored for dopamine detection. Among these, electrochemical methods are particularly promising due to their simplicity, efficiency, and rapid detection capabilities[ 6 ], [ 7 ]. However, a significant challenge arises from the coexistence of interfering biomolecules such as ascorbic acid (AA) and uric acid (UA), which share similar oxidation potentials with dopamine. This overlap complicates the selective and sensitive electrochemical detection of dopamine, making the development of advanced detection methods an ongoing necessity[ 8 ], [ 9 ], [ 10 ]. To tackle this problem, the development of sensitive, selective and reliable electrochemical sensors for dopamine detection has become a critical area of research. Based on the superior geometrical and chemical properties, the carbon nanomaterials, have become essential tools in the development of electrochemical sensors[ 11 ], [ 12 ]. Graphene, which is two-dimensional carbon material that is widely used in sensors and biosensors, capacitors, and energy conversion/storage systems because of its high specifics surface area, good chemical stability, electron mobility, and excellent electrical and thermal conductivity[ 13 ], [ 14 ]. Although graphene possesses exceptional chemical and physical properties, such as high surface area, mechanical strength, and excellent thermal and electrical conductivity, its derivatives, graphene oxide (GO) and reduced graphene oxide (RGO), have garnered increasing attention in recent years. This is due to their versatility in applications like electroanalytical chemistry, electrocatalysis, and electrochemical sensors, as well as their role as effective precursors for graphene synthesis[ 15 ], [ 16 ]. Modified electrodes with metal nanoparticles (NPs) have gained significant attention in electroanalysis due to their excellent biocompatibility, large surface area, and catalytic properties. In particular, graphene-based materials decorated with metal NPs have emerged as crucial components for sensor development, as they exhibit synergistic electrocatalytic behaviour derived from the combination of graphene’s unique properties and the catalytic efficiency of metal NPs. Reduced graphene oxide (RGO), with its defects and oxygen functional groups (-OH, C = O, -COOH), serves as an excellent scaffold for forming graphene-metal hybrid nanocomposites with enhanced performance. Recently, many graphene-metal nanocomposites have been proposed for use in electrochemical biosensors. However, conventional RGO synthesis, typically achieved via chemical reduction using toxic agents, poses environmental and health risks. Similarly, the drop-casting method commonly employed for electrode modification introduces inconsistencies in film thickness and internal structure, further complicating reproducibility. Moreover, the preparation of RGO composites often involves time-intensive and complex processes[ 17 ], [ 18 ], [ 19 ]. Consequently, researchers are investigating advanced methods to overcome the current challenges associated with graphene-based hybrid nanocomposites. One promising technique gaining attention is electrodeposition, which offers a simple, cost-effective, and environmentally friendly alternative to traditional methods. This approach not only eliminates the need for toxic reducing agents but also avoids high temperature processes, making it a more sustainable option for the synthesis of reduced graphene oxide (RGO) and its composites[ 15 ], [ 20 ], [ 21 ]. This study investigates the optimisation of fabrication settings for pristine reduced graphene oxide (RGO) on screen-printed gold electrodes (SPGEs) for the detection of the dopamine biomarker. It especially examines the impact of graphene oxide (GO) concentration and synthesis temperature on the electrodeposition process. The evaluation of the RGO/SPGE sensor's performance for dopamine detection was conducted using cyclic voltammetry (CV) and square wave voltammetry (SWV). The sensor's sensitivity, stability, reproducibility, resistance to interference, and repeatability underwent comprehensive examination and analysis. The process of electrodeposition facilitates the precise reduction of graphene oxide (GO) to reduced graphene oxide (RGO) directly on the electrode surface. This method enhances adhesion, conductivity, and ensures the development of a uniform and electrochemically active RGO layer. 2.0 Experimental 2.1 Reagents and Chemicals Graphene oxide (GO) powder was purchased from GO Advanced Solutions Sdn. Bhd (Selangor, Malaysia). Phosphate Buffer Saline (PBS) pH 7.4 was obtained from R&M Chemicals (United Kingdom). Sodium hydroxide (NaOH) from Merck (Darmstadt, Germany). Dopamine hydrochloride was from Sigma Aldrich (Missouri, US). 2.2 Optimization of Reduced Graphene Oxide. The reduced graphene oxide (RGO) was synthesized from graphene oxide (GO) powder, with the pH maintained at pH 9 [ 22 ] for all GO solutions throughout the experiment, to determine the optimal synthesis conditions for the detection of dopamine. First, GO solutions were prepared at concentrations of 333 mgmL⁻ 1 , 500 mgmL⁻ 1 and 667 mgmL⁻ 1 . These solutions were electrodeposited onto screen-printed gold electrode (SPGE), and the optimum concentration was identified through characterization of the deposited RGO. After determining the optimal concentration, the electrodeposition process was performed at water bath temperatures of 40°C, 50°C, and 60°C. The determinations of the ideal water bath temperature for the RGO synthesis were identified using the same characterization method. All the electrodeposition process were carried out at potential value of -0.1 V to -1.4 V at 5 mVs⁻ 1 scan rate for 10 deposition cycles. 2.3 Instrumentation. The electrodeposition of RGO was performed using a Metrohm PGSTAT204 (Utrecht, Netherland) system with a three-electrode configuration. An Ag/AgCl electrode served as the reference electrode, a platinum wire acted as the counter electrode, and the screen-printed gold electrode (SPGE) functioned as the working electrode. Kapton tape was applied to mask the reference and counter electrode regions on the surface of the SPGE. the electrochemical measurements were conducted using a Metrohm Dropsens, with the SPGE connected to a connector. The characterization of RGO/SPGE was carried out using Field Emission Scanning Electron Microscopy (FESEM) with Energy Dispersive X-ray Spectroscopy (EDS), X-Ray Diffraction (XRD) and Raman spectroscopy. FESEM imaging was carried out using a TESCAN FESEM MAGNA microscope, operated at an accelerating voltage of 5kV. Prior to analysis, the samples were coated with a thin layer of platinum using a sputter coater to enhance the conductivity and prevent charging effects. The imaging was performed with in-beam secondary electron (SE) mode at a magnification of 15kx, with a working distance of 3.40mm. The field of view (FoV) was set to 18.6 µm to observe surface morphology and obtain high resolution images. All the images were captured under high vacuum conditions. For elemental analysis, EDS was performed using an Oxford Instruments integrated with the FESEM system, operated at 15kV. The elemental maps and point analyses were conducted to determine the composition of the sample. The data were processed using AZtec software, and elemental identification was performed based on the characteristic X-ray peaks detected in the spectrum. To investigate the crystalline structure, size, and chemical composition of the RGO on the SPGE, the surface was carefully cut to expose the working electrode to analyse the electrode’s active area where the deposition of RGO occur. The sample was analysed using XRD with a PANalytical X'pert PRO system (45 kV, 40 mA), scanned over a 2θ range of 5° to 90° at a scanning rate of 2°/min. Raman spectroscopy was performed using NTEGRA SPECTRA MT MDT system with a laser excitation wavelength of 514 nm to analyse the vibrational modes and structural properties of RGO. This method provided the information on the D (~ 1350 cm -1 ), G (~ 1580 cm -1 ) and 2D (~ 2700 cm -1 ) bands, which are associated with the degree of graphitization, defect density and layer structure. The D band corresponded to the structural defects and disorder while the G band indicated the sp 2 graphitic domains. The 2D band (~ 2694 cm⁻¹), a second-order overtone of the D band, is due to a two-phonon scattering process at the K point of the Brillouin zone. Its intensity and shape reveal information about the number of graphene layers and their stacking order[ 23 ]. The intensity ratio (ID/IG) which indicate the defect density and degree of reduction was analysed to obtain the optimize synthesis condition. 2.4 Electrochemical detection of dopamine The electrochemical detection of dopamine was optimised at several pH (5.0, 6.0, 7.4, 8.0, 9.0). The optimum pH for the dopamine detection was analysed using cyclic voltammetry (CV). The cyclic voltammetry (CV) and square wave voltammetry (SWV) were employed to evaluate the electrode's response to dopamine. For CV, measurements were taken from a potential range of -0.3 V to + 0.8 V at a scan rate of 50 mVs -1 . SWV measurements involved a positive potential sweep from − 0.2 V to + 0.4 V, with a step potential of 10 mV, a pulse amplitude of 15 mV, and a frequency of 10 Hz. Electrochemical impedance spectroscopy (EIS) was performed at the open circuit potential (OCP), between 0.044 V to 0.010 V depend on the dopamine concentration. The frequency range used for EIS measurements was from 100 kHz to 100 mHz, with a sinusoidal amplitude of 10 mV. Conducting EIS at the OCP allowed for the characterization of the natural electrode-electrolyte interface without the influence of external potential perturbations, offering valuable insights into the equilibrium interactions of dopamine with the electrode surface, such as adsorption and double-layer effects. 3.0 Results and Discussion 3.1 Surface characterization of RGO modified electrode surface. 3.1.1 Effect of Graphene Oxide (GO) concentration towards RGO formation. The advancement of high-performance electrochemical sensors requires the optimisation of sensing electrode materials. This research aims to enhance the optical and electrical properties of RGO on screen-printed gold electrodes (SPGEs) via the regulated electrodeposition technique. To attain optimal RGO deposition, the concentration of the GO solution and the temperature of the water bath were methodically altered. Figure 1 presents a morphological analysis, showcasing FESEM images of electrodeposited reduced graphene oxide (RGO) on a screen-printed gold electrode (SPGE) at different concentrations of graphene oxide (GO) solution. The findings indicate a substantial link between the concentration of GO and the synthesis of RGO on SPGE. All FESEM images exhibited a consistent morphology, with RGO forming in the interstices between the gold nanostructures on the SPGE, achieved through direct adhesion to the gold surfaces under all experimental circumstances. At the minimal concentration of 333 mgmL⁻1, initial RGO production was detected within the interstices of the gold nanostructures. As the concentration increased to 500 mg mL⁻1, the coverage of RGO extended, resulting in a more significant presence on the electrode surface. Increasing the concentration to 667 mgmL⁻1 achieved total surface coverage, along with the formation of holes and ripples that signify RGO aggregation[ 24 ]. A thorough grasp of the material composition is essential to confirm the presence of carbon (C) in RGO. Table 1 presents essential elemental data, providing a detailed quantitative analysis of atomic percentages and the C:O ratio, which is crucial for RGO characterization. An analysis of the C:O ratio indicates an improvement following RGO electrodeposition across all concentrations, except for the lowest ratio. The C:O ratio for GO powder was determined to be 401, whereas the values for RGO at concentrations of 333 mgmL⁻ 1 , 500 mgmL⁻ 1 , and 667 mgmL⁻ 1 were found to be 2.34, 12.56 and 4.97 respectively. except for the 333 mgmL⁻ 1 sample, the other samples showed a diminished presence of functional groups in comparison to GO powder. This is due to the fact that during the electrodeposition process, the quantity of GO available for deposition was lower in comparison to the other concentrations (500 mgmL⁻ 1 , 667 mgmL⁻ 1 ). Consequently, at a concentration of 333 mgmL⁻1, the electrodeposited reduced graphene oxide (RGO) fails to sufficiently develop and occupy the gap on the surface of the screen-printed graphite electrode (SPGE). The results obtained were consistent with the FESEM results presented in Fig. 1 . The electrodeposited RGO exhibits structural properties that are intermediate between those of graphene oxide and graphene. This is because RGO has been only partially removed of its oxygen functional groups and is left with structural imperfections that do not allow it to attain the ideal structure of graphene[ 25 ]. Table 1 Summary of EDS analysis for different GO solution concentration Concentration (mgmL⁻ 1 ) Carbon (%) Oxygen (%) C:O Ratio 333 43.54 18.61 2.34 500 50.35 4.01 12.56 667 51.87 10.45 4.97 X-ray diffraction (XRD) was employed to investigate the modifications in interlayer spacing within graphene-related materials of the fabricated electrode. Although reduced graphene oxide (RGO) and graphene oxide (GO) are both composed of carbon atoms, the XRD patterns reveal distinct differences due to variations in atomic arrangement. Figure 2 (a) presents the XRD patterns for GO powder and RGO at different electrodeposition concentrations. The GO powder exhibits a characteristics diffraction peak at 2θ = 11.47°, which is attributed to its oxidized structure with a high degree of interlayer spacing caused by oxygen functional groups and water intercalation[ 26 ]. As a result of electrodeposition of RGO, this GO peak completely diminishes which confirm the removal of oxygen-containing functional groups and structural formation of RGO. At the same time, the broad peak at 2θ = 22.8°, (Fig. 2 (b)) which are already present in GO, remains in RGO. The peak which corresponds to the (002) plane of a graphene-like structure shows a decrease in the interlayer spacing due to the removal of some oxygen containing functional groups indicating the reestablishment of sp2 network on reduction. The broad peak may be due to RGO retains some structural disorder and does not achieve complete graphitization[ 27 ]. In contrast, the XRD pattern of gold, a crystalline material, showed well-defined peaks at 2θ = 38.38°, 44.62°, 64.88°, 77.97°, and 82.19°, corresponding to the (111), (200), (220), (311), and (222) planes of the gold nanostructure [ 28 ]. These peaks confirm its crystalline nature, which serves as a conductive platform for RGO deposition. Raman spectroscopy was employed to analyse the structural properties of RGO electrodeposited at varying concentrations (333 mgmL⁻ 1 , 500 mgmL⁻ 1 and 667 mgmL⁻ 1 ). The Raman spectra is shown in Fig. 3 highlighting the D (~ 1350 cm − 1 ) and G (~ 1580 cm − 1 ) bands which are the indications of the structural defects and graphitic domains, respectively. Intensity ratio (I D /I G ) is the important parameter for the assessment of the defect density. The intensity ratio was calculated and tabulated in Table 2 . At 333 mgmL⁻ 1 , the I D /I G ratio was 1.38, which is the lowest compared to 500 and 667 mgmL⁻ 1 . This is because at low concentration, the GO sheets available may be less for deposition process which results in a thinner RGO layer with fewer defects. The thin RGO layer may have a larger and more continuous sp 2 domains with less structural defects which explains the low I D /I G ratio. However, at 500 mgmL⁻ 1 , the I D /I G ratio increased to 1.72, which is higher than at 333 mgmL⁻ 1 , indicating better exfoliation of GO during the reduction process. This led to a decrease in the average size of sp² domains and the introduction of more structural defects. In addition, the increase in structural defects indicates that the number of active sites on RGO has increased, leading to better conductivity of the RGO film [ 29 ]. The I D /I G ratio for 667 mgmL⁻ 1 shows a slight decrease from 1.72 (at 500 mgmL⁻ 1 ) to 1.62, indicating that at higher GO concentrations, the electrodeposition process forms a thicker RGO layer. This increased thickness may lead to agglomeration, where defects become distributed within the bulk material rather than remaining on the surface. As a result, fewer defects are detected at the surface, leading to a lower D-band intensity in Raman analysis [ 30 ]. This trend is consistent with FESEM images, which show increased film thickness and possible sheet stacking at higher GO concentrations. Table 2 Raman spectra analysis of I D /I G for different concentration of Graphene Oxide (GO) solution 333 mgmL⁻ 1 , 500 mgmL⁻ 1 , 667 mgmL⁻ 1 . Concentration (mgmL⁻ 1 ) D G I D /I G 333 182844.28 132332.23 1.38 500 134635.70 78073.65 1.72 667 107109.68 66163.54 1.62 3.1.2 Effect of electrodeposition temperature on RGO formation. The prior characterisation results indicate that the ideal concentration for the synthesis of reduced graphene oxide (RGO) is 500 mg/mL. This concentration appears to facilitate the reduction process, resulting in a more distinct RGO structure relative to other concentrations. Consequent to this discovery, a concentration of 500 mg mL⁻¹ of GO was selected for subsequent investigations pertaining to temperature. Through the analysis of temperature's effect on the properties of RGO at its optimal concentration, a deeper comprehension of RGO's thermal stability and structural integrity can be gained, both of which are vital for its prospective applications. FESEM was used to analyse the morphology of RGO electrodeposited on screen-printed gold electrodes (SPGE) at various temperatures. The images in Fig. 4 illustrate the relationship between deposition temperature and RGO formation. The RGO deposits both within the interstices and on the surface of the SPGE, bonding directly to the gold surfaces under all experimental conditions, similar to what was observed in the concentration variation analysis. There is a strong correlation between deposition temperature and the density of RGO formation on SPGE. FESEM analysis indicates that as the electrodeposition temperature increases, the amount of RGO deposited on the SPGE surface also rises. At 40°C, RGO formation is evident within the gaps of the gold nanostructures. By 60°C, the RGO density increases, covering a significant portion of the gold surface. However, despite the higher density, the RGO does not completely fill the gaps, suggesting that at elevated temperatures, the reduction process occurs more rapidly, potentially leading to less uniform deposition. This highlights the importance of optimizing deposition temperature for achieving a well-structured RGO layer. Table 3 presents the elemental composition of RGO deposited at different temperatures which are 40°C, 50°C, and 60°C. The table highlight the variations in carbon and oxygen content, as well as the corresponding carbon-to-oxygen (C:O) ratio. The results shows that the reduction temperature significantly influences the chemical structure of RGO formation. At 40°C, the RGO shows the highest carbon content which is 50.35% and the lowest oxygen content at 4.01% which displays a high C:O ratio at 12.56. The high C:O ratio indicate an efficient reduction process with a well-preserved graphene structure and significant elimination of oxygen-functional groups [ 31 ]. However, at 50°C, the lowest C:O ratio of 2.47 was obtained with a decrease in carbon content from 50.35–32.76% while an increase in oxygen content to from 4.01 to 13.3%. This suggests that reduction was less successful at 50°C, which might be due to oxygen-trapped defects formed or because oxygen functional groups were not completely removed. As the temperature of the water bath was increased to 60°C, both carbon and oxygen content increased to 49.07% and 11.52% respectively which leads to higher C:O ratio of 4.26 in comparison to 50°C which shows that the removal of oxygen content in 60°C is better than 50°C. Nevertheless, the reduction process's efficiency did not rise in proportion to temperature. This could be because at higher temperature, the competing effects occurs such as defects formation, structural re-oxidation or an altered reduction kinetics[ 32 ]. Table 3 Summary of EDS analysis for different temperature. Temperature Carbon (%) Oxygen (%) C:O Ratio 40°C 50.35 4.01 12.56 50°C 32.76 13.3 2.47 60°C 49.07 11.52 4.26 The diffraction pattern of GO and RGO treated at different temperatures is shown in Fig. 5 . Diffraction pattern of GO has two diffraction peaks at 11.47 (001) as the characteristic peak and 22. (002) [ 33 ]. The diffraction pattern of RGO shows no characteristics peak of GO at 11.47. This is due to the removal of oxygen functional groups such as hydroxyl and carboxylate which indicate the structural changes from GO to RGO with a reduction in basal spacing. The diffraction peak of RGO appear at 22.6° which confirm the successful reduction process. The peak broadening of all RGO samples indicates a structural disorder and small graphitic domains. Diffraction patterns of all samples are similar, but different reduction temperatures may affect the extent of graphitization and defect density. Figure 6 presents the Raman spectra of RGO subjected to treatment at different temperatures ranging from 40°C to 60°C. The three prominent peaks, specifically the D, G, and 2D bands, are situated at 1350 cm⁻¹, 1580 cm⁻¹, and 2694 cm⁻¹, correspondingly. The Raman spectra were utilised to conduct a qualitative analysis of the extent of imperfections in the graphitic lattice as displayed in Table 4 . The intensity of the D peaks, which represents the vibrations of sp³-hybridized carbon atoms in disordered graphene, decreased as the temperature increased. This reduction indicates that at elevated temperatures, a substantial portion of the imperfections in the graphene material had been rectified[ 34 ]. This is due to the removal of oxygen-containing functional groups which restores sp2 hybridized carbon domains that lead to improve the structural order [ 35 ]. The simultaneous decline in the G peaks indicates the alterations in the structure and the decrease in the size of the sp 2 domain. Nevertheless, it is evident that the strength of G peaks diminishes as the temperature rises. This suggests that elevated temperatures can facilitate the generation of imperfections in the graphene lattice. Furthermore, the I D /I G ratio exhibited little changes, indicating that the ratio of sp 2 and sp 3 hybridised carbon atoms was not significantly influenced by the rise in temperature. These findings indicate that although the overall structural strength of the sample decreases as temperatures rise, the basic graphitic character of the material remains intact. Table 4 Quantitative analysis of Raman spectra of I D /I G for different water bath temperature of 40°C, 50°C, 60°C. Temperature (˚C) D G I D /I G 40 134635.70 78073.65 1.72 50 99661.95 60812.75 1.64 60 90319.43 55285.40 1.63 3.2 Electrochemical sensing of dopamine 3.2.1 Effect of RGO/SPGE on Dopamine detection. Cyclic voltammetry (CV) was utilized to investigate the electrochemical behavior of electrodeposited reduced graphene oxide (RGO) on SPGE. Figure 7 (a) illustrates the electrochemical characteristics of SPGE and RGO/SPGE in deionized water and phosphate-buffered saline (PBS). In deionized water, both SPGE and RGO/SPGE demonstrate the absence of redox reactions, as no redox peaks are detected on the CV curve. Nevertheless, the higher electroactive surface area of the RGO/SPGE results in a more extensive CV plot, which is ascribed to its enhanced capacitive current [ 36 ]. In PBS (pH 7.4), the CV curve of SPGE shows a reduction peak in the absence of dopamine. This is due to the behavior of the gold surface. The SPGE may display reduction peaks in phosphate buffer as a result of surface interactions between phosphate ions and the gold electrode. This interaction may entail the adsorption of phosphate molecules, succeeded by electron transfer processes at the gold surface, leading to discernible peaks in the CV curve. This suggests that the reduction peak detected in bare SPGE was probably attributable to the redox-active characteristics of the gold surface in phosphate buffer [ 37 ]. The CV curve of RGO/SPGE in PBS exhibits an enhancement in reduction current relative to SPGE, along with the emergence of an oxidation peak. This results from the augmentation of electroactive surface area and enhanced electron transfer kinetics attributable to the presence of the RGO layer. The presence of RGO enhances the electrode's conductivity and increases the number of active sites, leading to a greater current response. The oxidation peak may result from residual oxygen-containing functional groups on RGO or interfacial phenomena at the electrode surface [ 38 ]. In the presence of 1mM dopamine in PBS (pH 7.4), Fig. 7 (b) SPGE and RGO/SPGE exhibited redox peaks which correspond to the oxidation of dopamine to dopamine-quinone and its subsequent reduction. In comparison to SPGE, the RGO/SPGE showed more well-defined redox peaks and significantly higher peak currents. This indicates that the presence of RGO enhanced the electrochemical response towards dopamine due to the high surface area, good electrical conductivity, and efficient π–π interactions between its sp² carbon domains and the dopamine's aromatic ring improved the electrochemical response to dopamine. These properties of RGO provided faster electron transfer and increased the number of electroactive sites available for dopamine detection[ 39 ]. The FTIR analysis was performed to study the chemical structure and functional groups in GO, SPGE, RGO/SPGE, dopamine as well as the interaction between dopamine and RGO/SPGE after electrochemical testing as shown in Fig. 8 . The FTIR spectrum of GO shows several characteristic peaks which confirms its oxygenated structure. The peak appears at 1040, 1250, 1376, 1610, 1707 and 3227 cm − 1 which are attributed to C–O stretching, C–O stretching, O–H bending, C = C aromatic stretching, C = O stretching, and O–H stretching respectively[ 40 ], [ 41 ]. For bare SPGE, the previous study reported the absence of the characteristic peaks in the FTIR spectrum due to its inert surface. However, in this work, the peaks were observed at 1121, 1376, 1654 and 1787 cm − 1 . These peaks were more likely due to impurities[ 42 ] and instrumental noise[ 43 ]. The FTIR spectrum of RGO/SPGE shows significant change after the reduction of GO. The appearance of peaks at 999, 1303, 1596, 1704, 2341, 2599 and 3100 cm − 1 shows structural changes of GO. The disappearance of the peak at 1376 cm − 1 which correspond to O-H bending and the reduction of peak at 1250 and 1707 cm − 1 further confirms the successful reduction of GO. The peak observed at 1610 cm − 1 in GO which is attributed to C = C stretching of sp2 hybridized carbon, shift slightly to 1596 cm − 1 in RGO/SPGE. The shift confirms the restoration of the conjugated sp 2 -hybridized carbon domain during the reduction process. Furthermore, the broad peak at 3227 cm − 1 in GO, corresponding to O-H stretching, shifts and weakens to 3100 cm − 1 , indicating the decrease in hydroxyl group after the reduction of GO[ 40 ], [ 44 ]. Furthermore, the chemical structure and functional groups after electrochemical testing with dopamine was also being studied using FTIR analysis. The RGO/SPGE spectrums first showed distinctive peaks at 999, 1303, 1596, 1704, 2341, 2599 and 3100 cm − 1 , which corresponded to functional groups that included oxygen functional groups such as C-O, C = C, C = O and O-H. After dopamine testing, only a single peak remained at 999 cm − 1 which shows the alteration of the RGO/SPGE surface. The disappearance of peak at 1704 cm − 1 (C = O), 1596 cm − 1 (C = C) and 3100 cm − 1 (O-H) aligned with previous study that shows the structural changes due to the dopamine reacting with the functional groups of RGO/SPGE surface. The remaining peak at 999 cm − 1 may indicate a shift in C-O stretching or a new vibrational environment resulting from the dopamine interaction[ 45 ]. These FTIR results are consistent with the CV findings where a significant current response was observed which indicate the electrochemical interaction between dopamine and the RGO/SPGE surface. 3.1.2 The effect of pH on Phosphate Buffer Solution (PBS). Cyclic voltammetry (CV) was employed to investigate the effect of pH on the electrochemical behaviour of reduced graphene oxide modified screen-printed gold electrodes (RGO/SPGE) in dopamine (DA) sensing. As shown in Fig. 9 , CV plots were obtained for RGO/SPGE in a 1 mM DA solution throughout a pH range from 5.0 to 9.0. Each pH value produced distinct oxidation peak currents (I pa ) and oxidation peak potentials (E pa ), indicating that the electrochemical response of DA is strongly dependent on pH. Figure 10 shows the variation of I pa and E pa with pH. From the data shown in curve (a) of Fig. 10 , it is clear that Ipa increased from 19.960 µA at pH 5.0 to a maximum of 30.025 µA at pH 7.4, before decreasing back to 18.867 µA at pH 9.0. Thus, it can be inferred that maximum dopamine oxidation takes place at pH 7.4. This condition can be best explained by the possible equilibrium between protonation of dopamine and surface interaction with the electrode leading to better electron transfer. Consequently, pH 7.4 was chosen to serve as the supporting electrolyte in further electrochemical studies. Moreover, curve (b) in Fig. 10 shows that E pa decreases with increasing pH, demonstrating a linear trend. The linear relationship between E pa and pH is represented by the regression equation E pa = 0.614–0.054 pH, with a correlation coefficient of R² = 0.9945, which indicates a strong correlation between the oxidation peak potential and pH. The slope of -0.054 V/pH is close to the theoretical Nernstian value of -0.059 V/pH which indicates that the dopamine oxidation process at RGO/SPGE involves an equal number of protons and electrons. This finding confirms that the redox mechanism of dopamine on RGO/SPGE follows a well-established electrochemical principle[ 1 ]. The detection of dopamine (DA) on RGO/SPGE operates through a specific mechanism. In a phosphate buffer solution (PBS) with pH 7.4, most of the dopamine exists in a protonated state (DAH+) which significate that the molecule carries a positive charge. Due to the aromatic nature of the molecule, it is capable of associating with the π-electron rich area of RGO by virtue of the π-π stacking. At the same time, the electropositive nature of dopamine facilitates electrostatic attractions to the negatively charged oxygen-containing groups of the RGO. The resulting combination of these interactions promotes the adsorption of dopamine on the membrane’s surface which in turn enhances the ease of electron transfer. During this process, dopamine undergoes oxidation to dopamine-quinone, which generates a measurable current, enabling the detection of dopamine with high accuracy [ 46 ], [ 47 ]. The mechanism of dopamine detection was shown in Fig. 11 . Based on the CV plot of dopamine from Fig. 7 , the oxidation peak of dopamine was observed to appear in between potential of 0.1 to 0.2 V. The analytical signals obtained from the CV plot was used as a reference for the determination of dopamine. The electrochemical detection of dopamine with RGO/SPGE was examined in PBS containing dopamine at different concentrations starts from 0.003–0.05 mM using square-wave voltammetry (SWV) method in the potential region from − 0.2 to 0.4 V. As observed from Fig. 12 (a), as the dopamine concentration increases, the peak current also rises, and a distinct oxidation peak near 0.1 V becomes sharper and more intense at higher concentrations which confirm the RGO/SPGE’s excellent electrocatalytic activity for dopamine oxidation. As shown in the derived Fig. 12 (b), the peak current (I p ) is linearly depended on the concentration of dopamine with a regression equation of I p (µA) = 56.274 [Dopamine] + 0.1231 with high correlation coefficient (R 2 = 0.9765). The sensitivity of RGO/SPGE was found to be 511.58 µA mM⁻¹cm⁻². The limit of detection (LOD) is defined as LOD = 3S B /b, where S B is the standard deviation for the blank signal and b is the slope of the linear regression equation. S B was calculated by 3 repetitive experiments in blank PBS which resulted with the LOD of 1.2 µM. Table 5 presents a comparative analysis of the sensitivity of the dopamine sensor developed in this study against those reported in recent literature. The RGO/SPGE sensor fabricated in this work shows a remarkable sensitivity of 511.58 µA mM⁻¹cm⁻² which is notably higher compared to the previously reported graphene-based and composite sensor. The enhanced performance indicates the effectiveness of the electrodeposited RGO on SPGE in increasing the electrochemical response towards dopamine which make it as a highly competitive platform for sensitive dopamine detection. Table 5 Summary of sensitivity performance between this work and previously published dopamine sensors. Structure Detection method Linear range (mM) Sensitivity (µA mM⁻¹cm⁻²) LOD References RGO-AuNPs Square-wave voltammetry 0.0001–0.02 6.02 0.075 [ 10 ] RGO-PtNPs Square-wave voltammetry 0.0001–0.01 7.19 0.062 [ 10 ] ZIF-67/rGO Amperometry 0.00025–0.06625 93.7 0.052 [ 19 ] ZnO/CuO Amperometry 0.001–8 90.9 0.1 [ 48 ] MIL-101(Cr)-SO 3 H/PEI-rGO Amperometry 0.00025–0.23875 327.7 0.07 [ 49 ] PVA-ZnO Cyclic voltammetry (CV) 0.1–0.6 18.22 120.8 [ 50 ] Ga2O3⋅ZnO@SWCNT Amperometry 0.001–4.52 253.6 0.052 [ 51 ] In2O3⋅ZnO@MC Amperometry 0.0005–2.056 215.3 0.024 [ 52 ] CuNi-MOF@rGO Amperometry 0.001–0.5 19 9.41 [ 53 ] RGO/SPGE Square-wave voltammetry 0.003–0.05 511.58 1.2 This work 3.1.3 EIS Analysis of RGO/SPGE in in Dopamine Detection. Electrochemical impedance spectroscopy (EIS) is a crucial technique to investigate the interaction mechanisms between dopamine (DA) concentrations and electrode surfaces. This method provides comprehensive insights into fundamentals processes, including electron transfer kinetics, mass transport via diffusion, and surface phenomena such as adsorption. In addition, EIS allows the assessment of the electrical conductivity of the sensor which make it as an effective technique for characterizing the complex electrochemical behaviour of DA detection and analysis. The Nyquist plot for the electrochemical oxidation of DA shown in Fig. 13 (a) displayed the characteristics behaviour of the oxidation process, featuring two distinct semicircles. The Nyquist plot was fitted and analysed using the equivalent circuit model as shown in Fig. 13 (b). The circuit comprises key elements such as solution resistance (R s ), film resistance (R 1 ) and charge transfer resistance (R 2 )[ 54 ]. The parameters obtained from the fitted Nyquist plot was tabulated in Table 6 . The decreases in the charge transfer resistance values as the concentrations of DA increases were proved by the reduction of the second semicircles in the Nyquist plot. This phenomenon was caused by the increase in the availability of the electroactive dopamine molecules which facilitates the redox reaction. When the availability of the electroactive dopamine molecules increases, the electron transfer kinetics on the electrode surface increase which causing the resistance value decreases. The charge transfer resistance value was also plotted against the concentration of DA. The calibration plot shows a strong inverse linear relationship between the charge transfer resistance and DA concentrations which was indicated by the high regression coefficient (R 2 = 0.9896). The regression value shows the RGO/SPGE ability to accurately detect and quantify DA based on its impact on charge transfer kinetics. The results obtained from SWV and EIS align closely which revealed a strong relationship between current response and charge transfer resistance. The increase in peak current observed in SWV is directly correlated with the charge transfer resistance from the EIS results. As the charge transfer resistance decreases, the electron transfer kinetics improves which is reflected in the higher current response shown in the SWV results. Table 6 Solution Resistance (Rs), Film Resistance (R1), Charge transfer Resistance (R2) and Constant Phase Element (CPE) value obtained from the Nyquist Plot and equivalent circuit model. Concentrations (mM) Rs (Ω) R1(Ω) R2 (Ω) CPE (Ω -1 ms n ) 0.003 41.588 1503.8 829710 7.2326 0.006 41.574 1175.0 732800 5.494 0.008 41.641 2346.0 703790 6.2566 0.01 41.814 2975.7 668590 5.9844 0.015 41.750 3525.1 525000 5.8612 0.03 41.613 2966.8 264580 4.0273 0.05 41.850 3423.7 242530 3.9747 3.1.4 Interference study Selectivity is a crucial analytical parameter, particularly for electrochemical sensors designed to operate in complex biological samples where interference from coexisting species can significantly affect detection accuracy. In the case of dopamine (DA) detection, challenges arise due to the overlapping oxidation potentials of common interferences like uric acid (UA) and ascorbic acid (AA), which are often present in higher concentrations in biological fluids[ 55 ]. This interference can compromise sensor performance, making selectivity evaluation essential. To assess the selectivity of the RGO/SPGE sensor, individual voltammograms of DA (0.07mM), UA (0.4mM), and AA (1mM) were recorded, along with the voltammogram of their mixture, as shown in Fig. 14 . The results reveal that DA and UA exhibit distinct and well-defined oxidation peaks at 0.17 V and 0.31 V respectively, while AA presents a broad, indistinct peak lacking a sharp maximum at 0.14 V. In the mixture, the peak current of DA remains unaffected by the presence of UA and AA, as indicated by the consistent peak height of DA. Even at the same potential as AA, the peak current of dopamine shows no significant change. This behaviour may be attributed to an interaction between the amino group of the DA molecule and the sensor surface, which likely inhibits the oxidation of AA. These results demonstrate the ability of the RGO/SPGE sensor to effectively differentiate DA from other analytes, highlighting its high level of selectivity. Such performance is particularly valuable in complex matrices where precise and independent detection of DA is essential. 3.1.5 Stability, reproducibility and repeatability of RGO/SPGE The reproducibility of the sensor is a crucial parameter in assessing the performance of electrochemical devices. To evaluate the reproducibility of the RGO/SPGE, successive square wave voltammetry (SWV) measurements were conducted using five different electrodes. As shown in Fig. 15 (a), the response currents exhibited a relative standard deviation (RSD) of 4.04% (n = 3), indicating the excellent reproducibility of the RGO/SPGE and confirming its reliability and consistency in electrochemical measurements. The stability of the RGO/SPGE was also assessed by storing it at room temperature for one week and measuring its current response to 0.07 mM DA solution, as shown in Fig. 15 (b). After one week, 91.75% of the initial current response was retained, demonstrating the good stability of the developed sensor. These results highlight the potential of the RGO/SPGE for long-term applications, although further studies on extended storage durations and varying environmental conditions would provide a more comprehensive understanding of its shelf life. To improve longevity, electrodes may require storage in optimal conditions, such as an inert atmosphere, low temperature, low humidity, or vacuum. In addition, the RGO/SPGE was evaluated for repetitive analysis through 15 consecutive measurements of DA determination, as depicted in Fig. 15 (c). The calculated RSD of 3.28% (n = 3) underscores the sensor's durability and consistent performance in repeated use. This impressive reproducibility and stability establish the RGO/SPGE as a reliable platform for electrochemical sensing, paving the way for its integration into practical applications, including real-time monitoring and clinical diagnostics. 4.0 Conclusion Pristine reduced graphene oxide (RGO) was effectively synthesised on a screen-printed gold electrode (SPGE) by an electrodeposition method, creating a highly efficient platform for dopamine detection. The optimisation of electrodeposition parameters, specifically the concentration of graphene oxide (GO) solution and the temperature of the water bath, indicated that optimal circumstances were a GO concentration of 0.5 mg/mL and a water bath temperature of 40°C. Under these optimised conditions, the RGO/SPGE sensor exhibited remarkable efficacy in dopamine detection via square-wave voltammetry (SWV), attaining a sensitivity of 511.58 µA mM⁻¹cm⁻² and a detection limit of 1.2 µM. Electrochemical impedance spectroscopy (EIS) corroborated these findings by demonstrating a reduction in charge transfer resistance as dopamine content increased. The sensor demonstrated exceptional selectivity for dopamine, accurately differentiating it from prevalent interfering substances like uric acid and ascorbic acid. The RGO/SPGE sensor demonstrated remarkable stability, reproducibility, and repeatability, as indicated by consistently low relative standard deviation (RSD) values throughout all experiments. The results underscore the developed sensor's promise as a dependable, swift, and sensitive instrument for dopamine detection, presenting intriguing applications in clinical diagnostics and biochemical analysis. Declarations Funding The authors express their gratitude for the support received from the Ministry of Higher Education Malaysia through the Fundamental Research Grant Scheme: 600-RMC/FRGS 5/3 (082/2023). 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6704266","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":462400133,"identity":"5a320421-9635-4731-b16e-b29db11417ba","order_by":0,"name":"Muhammad Haziq Ilias","email":"","orcid":"","institution":"Universiti Teknologi MARA, Shah Alam","correspondingAuthor":false,"prefix":"","firstName":"Muhammad","middleName":"Haziq","lastName":"Ilias","suffix":""},{"id":462400134,"identity":"9c9ece03-6e08-4268-903a-8f0d487a2ac1","order_by":1,"name":"Zainiharyati Mohd Zain","email":"","orcid":"","institution":"Universiti Teknologi MARA, Shah 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Zoolfakar","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA40lEQVRIiWNgGAWjYDACCSDmMfjPzM/A2ADiQ0jCWiqY2SUbGBsbSNByhpnf4ABENWEt/LO7Ez+8bWOTNr6R3P7oBoON7IYD3GkSeC25c3az5Nw2HmOzG4mNzTkMacYbDvBuw6uF4UbuBmneNolkqJbDiQS1yN/I3fybt82gfvMMsJb/hLUY3MjdJs1zJoHZQAKs5QBhLYZALZZzKg4wS5x52Dg7xyDZeOZh3s0W+LTIAR12443BAWb+9vQHn3Mq7GT7jvduvIFPC7o7gZiZgQV/iGEDzB9I1jIKRsEoGAXDGQAAYmNRpPf1rrsAAAAASUVORK5CYII=","orcid":"","institution":"Universiti Teknologi MARA, Shah Alam","correspondingAuthor":true,"prefix":"","firstName":"Ahmad","middleName":"Sabirin","lastName":"Zoolfakar","suffix":""}],"badges":[],"createdAt":"2025-05-20 06:23:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6704266/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6704266/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":83534356,"identity":"a24bcb3f-78ad-494e-b5bb-a364d418d28d","added_by":"auto","created_at":"2025-05-28 06:06:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":294192,"visible":true,"origin":"","legend":"\u003cp\u003eFESEM images of (a) Graphene Oxide (GO) Powder, (b) 333 mgmL⁻\u003csup\u003e1\u003c/sup\u003e GO (c) 500 mgmL⁻\u003csup\u003e1\u003c/sup\u003e GO, (d) 667 mgmL⁻\u003csup\u003e1\u003c/sup\u003e RGO on SPGE surface at magnification 15kx.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/096a73426c2fec01c07e95a4.png"},{"id":83534374,"identity":"4bfa083c-6ddb-4fb0-ae46-1d0aa9b6eb6d","added_by":"auto","created_at":"2025-05-28 06:06:23","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":85689,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e XRD pattern of GO Powder, 333 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, 500 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, 667 mgmL⁻\u003csup\u003e1\u003c/sup\u003e and \u003cstrong\u003e(b)\u003c/strong\u003e XRD pattern focused on RGO peak at 2θ = 5° to 30°\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/b3ac9d483ff276d559246e1a.png"},{"id":83534353,"identity":"6e0d3c74-e07c-48f6-b5cb-32ddd7c95cc6","added_by":"auto","created_at":"2025-05-28 06:06:15","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":52278,"visible":true,"origin":"","legend":"\u003cp\u003eRaman spectra for different concentration of Graphene Oxide (GO) solution 333 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, 500 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, 667 mgmL⁻\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/0c73046777158938cad74153.png"},{"id":83534359,"identity":"346d6761-eb2f-4e7d-bb89-d0466ad56be2","added_by":"auto","created_at":"2025-05-28 06:06:15","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":323241,"visible":true,"origin":"","legend":"\u003cp\u003eFESEM images of \u003cstrong\u003e(a) \u003c/strong\u003eGraphene Oxide (GO) Powder, \u003cstrong\u003e(b)\u003c/strong\u003e 40°C \u003cstrong\u003e(c)\u003c/strong\u003e50°C, \u003cstrong\u003e(d)\u003c/strong\u003e 60°C of water bath temperature during electrodeposition of RGO at magnification of 15kx.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/98d75da2e29dcba7b84f8751.png"},{"id":83534364,"identity":"78ffde3c-f204-4816-a297-5b885a883fdb","added_by":"auto","created_at":"2025-05-28 06:06:15","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":81363,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e XRD pattern for GO Powder and different water bath temperature (40C, 50C, 60C), \u003cstrong\u003e(b)\u003c/strong\u003e XRD pattern focused on RGO peaks at 2θ = 5° to 30°\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/f975da18c6427187f49119c9.png"},{"id":83534355,"identity":"b196760d-7720-4f42-8c23-0e007c463261","added_by":"auto","created_at":"2025-05-28 06:06:15","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":48993,"visible":true,"origin":"","legend":"\u003cp\u003eRaman spectra for different water bath temperature of 40°C, 50°C, 60°C\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/fc5ccb1875b5ae5b28853cb3.png"},{"id":83534361,"identity":"8390fa50-e384-43e3-8d33-fb5663745eb3","added_by":"auto","created_at":"2025-05-28 06:06:15","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":69424,"visible":true,"origin":"","legend":"\u003cp\u003eCV curve of SPGE and RGO/SPGE in \u003cstrong\u003e(a)\u003c/strong\u003e deionized water, phosphate buffer (PBS) (pH 7.4), and \u003cstrong\u003e(b)\u003c/strong\u003e 1mM dopamine in PBS (pH 7.4)\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/bb196109380044d9509aecb2.png"},{"id":83534932,"identity":"3d2731ce-4f91-4397-b9cd-dbdf7069fe3b","added_by":"auto","created_at":"2025-05-28 06:14:15","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":46178,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of (a) GO, (b) SPGE, (c) RGO/SPGE, (d) RGO/SPGE in the presence of 1mM dopamine in PBS (pH 7.4)\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/67308ef569231176d0885086.png"},{"id":83534369,"identity":"5b60e5de-74d1-45f2-bd09-3aa0953c89b0","added_by":"auto","created_at":"2025-05-28 06:06:15","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":111438,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic Voltammetry (CV) of RGO/SPGE towards 1mM of dopamine at pH 5.0, 6.0, 7.4, 8.0 and 9.0\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/822f928eca1800b21d182693.png"},{"id":83534371,"identity":"4f219b81-7f72-4528-8566-3e7e9d9ee871","added_by":"auto","created_at":"2025-05-28 06:06:15","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":35348,"visible":true,"origin":"","legend":"\u003cp\u003eRelation between (a) Ipa (solid line) and between (b) Epa (dotted line) and pH\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/e4009908e6cf16c3fb3d7f3d.png"},{"id":83534368,"identity":"22635855-1614-4e00-a474-f7fc1f66be6a","added_by":"auto","created_at":"2025-05-28 06:06:15","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":113061,"visible":true,"origin":"","legend":"\u003cp\u003eRedox mechanism of electrochemical detection of dopamine on RGO/SPGE at pH 7.4[1]\u003c/p\u003e","description":"","filename":"image11.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/1240d7336c673143128b6357.png"},{"id":83534362,"identity":"81ac4fd2-8d1c-41eb-80b6-7f5fa610cbfa","added_by":"auto","created_at":"2025-05-28 06:06:15","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":74375,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e SWV obtained at RGO/SPGE in 0.1 M PBS (pH 7.4) with different concentrations of DA (a to g: 0.003, 0.006, 0.008, 0.010, 0.015, 0.030, 0.050 mM respectively), scan rate 50 mVs⁻\u003csup\u003e1\u003c/sup\u003e. \u003cstrong\u003e(b)\u003c/strong\u003e The linear relationship between the peak current and DA concentrations\u003c/p\u003e","description":"","filename":"image12.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/1a745bf7432d44bbce2b1e5e.png"},{"id":83534365,"identity":"4ca517b1-56a9-4d80-8ed4-b119a932a5dd","added_by":"auto","created_at":"2025-05-28 06:06:15","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":114958,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e Nyquist plot of dopamine at different concentrations ranging from 0.003 to 0.05 mM in PBS (pH 7.4), Inset: The Nyquist plot of dopamine at higher frequency. \u003cstrong\u003e(b)\u003c/strong\u003eLinear relationship between DA concentrations and charge transfer resistance, \u003cstrong\u003einset:\u003c/strong\u003ethe equivalent circuit generated from the Nyquist plot\u003c/p\u003e","description":"","filename":"image13.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/53b2764b652d7db8f1498181.png"},{"id":83534358,"identity":"b6a65c62-7674-43e0-8239-3ac56be91ef2","added_by":"auto","created_at":"2025-05-28 06:06:15","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":66519,"visible":true,"origin":"","legend":"\u003cp\u003eSWV detection of Ascorbic Acid (AA) (1 mM), Dopamine (DA) (0.07 mM), Uric Acid (UA) (0.4 mM) and a mixture of AA,DA,UA\u003c/p\u003e","description":"","filename":"image14.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/1711692fd457dc7bab78a87b.png"},{"id":83534366,"identity":"3d97b0b6-bf57-4b15-a4c6-d9ce105d7a54","added_by":"auto","created_at":"2025-05-28 06:06:15","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":41112,"visible":true,"origin":"","legend":"\u003cp\u003e(a) reproducibility, (b) stability, and (c) repeatability analysis of RGO/SPGE using SWV with 0.07 mM DA in 0.1 M PBS (pH 7.4) with scan rate 50 mVs⁻\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"image15.png","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/66ae9132f007588ebf537f1c.png"},{"id":83535033,"identity":"ab14ad84-0a0e-42ab-ba32-b0c3042ce3d3","added_by":"auto","created_at":"2025-05-28 06:22:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2820693,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6704266/v1/26b9d546-fa36-4336-9dde-d203b6b3210e.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Highly Sensitive Dopamine Biochemical Sensor Employing Pristine Electrodeposited Reduced Graphene Oxide","fulltext":[{"header":"1.0 Introduction","content":"\u003cp\u003eDopamine (DA) (3,4-dihydroxyphenethylamine), an important neurotransmitter discovered by Arvid Carlsson in 1957, plays a pivotal role in various physiological and neurological processes. As a member of the biogenic amines class of neurotransmitters, DA facilitates the transmission of sensory signals between neurons via synapses, contributing to normal brain function[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. It influences multiple systems, including the cardiovascular, central nervous, endocrine, and renal systems, while also regulating physiological processes such as attention, learning, memory, movement, mood, behaviour, and mental cognition. Clinically, the accurate detection of dopamine is crucial for diagnosing and managing neurological disorders such as Parkinson\u0026rsquo;s disease, schizophrenia, depression, and attention deficit hyperactivity disorder (ADHD). An imbalance in dopamine levels in the brain is associated with neurodegenerative diseases, including Alzheimer\u0026rsquo;s and Parkinson\u0026rsquo;s, as well as mental health conditions like addiction and schizophrenia[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The ability to accurately monitor dopamine levels is critical for diagnosing and managing these conditions. Rapid, non-invasive, and highly sensitive detections methods could significantly improve early diagnosis and therapeutic interventions, offering better prevention.\u003c/p\u003e \u003cp\u003eSeveral analytical techniques, such as chemiluminescence, chromatography, colorimetric assays, fluorescence, and spectrophotometry, have been explored for dopamine detection. Among these, electrochemical methods are particularly promising due to their simplicity, efficiency, and rapid detection capabilities[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, a significant challenge arises from the coexistence of interfering biomolecules such as ascorbic acid (AA) and uric acid (UA), which share similar oxidation potentials with dopamine. This overlap complicates the selective and sensitive electrochemical detection of dopamine, making the development of advanced detection methods an ongoing necessity[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo tackle this problem, the development of sensitive, selective and reliable electrochemical sensors for dopamine detection has become a critical area of research. Based on the superior geometrical and chemical properties, the carbon nanomaterials, have become essential tools in the development of electrochemical sensors[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Graphene, which is two-dimensional carbon material that is widely used in sensors and biosensors, capacitors, and energy conversion/storage systems because of its high specifics surface area, good chemical stability, electron mobility, and excellent electrical and thermal conductivity[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Although graphene possesses exceptional chemical and physical properties, such as high surface area, mechanical strength, and excellent thermal and electrical conductivity, its derivatives, graphene oxide (GO) and reduced graphene oxide (RGO), have garnered increasing attention in recent years. This is due to their versatility in applications like electroanalytical chemistry, electrocatalysis, and electrochemical sensors, as well as their role as effective precursors for graphene synthesis[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eModified electrodes with metal nanoparticles (NPs) have gained significant attention in electroanalysis due to their excellent biocompatibility, large surface area, and catalytic properties. In particular, graphene-based materials decorated with metal NPs have emerged as crucial components for sensor development, as they exhibit synergistic electrocatalytic behaviour derived from the combination of graphene\u0026rsquo;s unique properties and the catalytic efficiency of metal NPs. Reduced graphene oxide (RGO), with its defects and oxygen functional groups (-OH, C\u0026thinsp;=\u0026thinsp;O, -COOH), serves as an excellent scaffold for forming graphene-metal hybrid nanocomposites with enhanced performance. Recently, many graphene-metal nanocomposites have been proposed for use in electrochemical biosensors. However, conventional RGO synthesis, typically achieved via chemical reduction using toxic agents, poses environmental and health risks. Similarly, the drop-casting method commonly employed for electrode modification introduces inconsistencies in film thickness and internal structure, further complicating reproducibility. Moreover, the preparation of RGO composites often involves time-intensive and complex processes[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Consequently, researchers are investigating advanced methods to overcome the current challenges associated with graphene-based hybrid nanocomposites. One promising technique gaining attention is electrodeposition, which offers a simple, cost-effective, and environmentally friendly alternative to traditional methods. This approach not only eliminates the need for toxic reducing agents but also avoids high temperature processes, making it a more sustainable option for the synthesis of reduced graphene oxide (RGO) and its composites[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThis study investigates the optimisation of fabrication settings for pristine reduced graphene oxide (RGO) on screen-printed gold electrodes (SPGEs) for the detection of the dopamine biomarker. It especially examines the impact of graphene oxide (GO) concentration and synthesis temperature on the electrodeposition process. The evaluation of the RGO/SPGE sensor's performance for dopamine detection was conducted using cyclic voltammetry (CV) and square wave voltammetry (SWV). The sensor's sensitivity, stability, reproducibility, resistance to interference, and repeatability underwent comprehensive examination and analysis. The process of electrodeposition facilitates the precise reduction of graphene oxide (GO) to reduced graphene oxide (RGO) directly on the electrode surface. This method enhances adhesion, conductivity, and ensures the development of a uniform and electrochemically active RGO layer.\u003c/p\u003e"},{"header":"2.0 Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Reagents and Chemicals\u003c/h2\u003e \u003cp\u003eGraphene oxide (GO) powder was purchased from GO Advanced Solutions Sdn. Bhd (Selangor, Malaysia). Phosphate Buffer Saline (PBS) pH 7.4 was obtained from R\u0026amp;M Chemicals (United Kingdom). Sodium hydroxide (NaOH) from Merck (Darmstadt, Germany). Dopamine hydrochloride was from Sigma Aldrich (Missouri, US).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Optimization of Reduced Graphene Oxide.\u003c/h2\u003e \u003cp\u003eThe reduced graphene oxide (RGO) was synthesized from graphene oxide (GO) powder, with the pH maintained at pH 9 [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] for all GO solutions throughout the experiment, to determine the optimal synthesis conditions for the detection of dopamine. First, GO solutions were prepared at concentrations of 333 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, 500 mgmL⁻\u003csup\u003e1\u003c/sup\u003e and 667 mgmL⁻\u003csup\u003e1\u003c/sup\u003e. These solutions were electrodeposited onto screen-printed gold electrode (SPGE), and the optimum concentration was identified through characterization of the deposited RGO. After determining the optimal concentration, the electrodeposition process was performed at water bath temperatures of 40\u0026deg;C, 50\u0026deg;C, and 60\u0026deg;C. The determinations of the ideal water bath temperature for the RGO synthesis were identified using the same characterization method. All the electrodeposition process were carried out at potential value of -0.1 V to -1.4 V at 5 mVs⁻\u003csup\u003e1\u003c/sup\u003e scan rate for 10 deposition cycles.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Instrumentation.\u003c/h2\u003e \u003cp\u003eThe electrodeposition of RGO was performed using a Metrohm PGSTAT204 (Utrecht, Netherland) system with a three-electrode configuration. An Ag/AgCl electrode served as the reference electrode, a platinum wire acted as the counter electrode, and the screen-printed gold electrode (SPGE) functioned as the working electrode. Kapton tape was applied to mask the reference and counter electrode regions on the surface of the SPGE. the electrochemical measurements were conducted using a Metrohm Dropsens, with the SPGE connected to a connector.\u003c/p\u003e \u003cp\u003eThe characterization of RGO/SPGE was carried out using Field Emission Scanning Electron Microscopy (FESEM) with Energy Dispersive X-ray Spectroscopy (EDS), X-Ray Diffraction (XRD) and Raman spectroscopy. FESEM imaging was carried out using a TESCAN FESEM MAGNA microscope, operated at an accelerating voltage of 5kV. Prior to analysis, the samples were coated with a thin layer of platinum using a sputter coater to enhance the conductivity and prevent charging effects. The imaging was performed with in-beam secondary electron (SE) mode at a magnification of 15kx, with a working distance of 3.40mm. The field of view (FoV) was set to 18.6 \u0026micro;m to observe surface morphology and obtain high resolution images. All the images were captured under high vacuum conditions.\u003c/p\u003e \u003cp\u003eFor elemental analysis, EDS was performed using an Oxford Instruments integrated with the FESEM system, operated at 15kV. The elemental maps and point analyses were conducted to determine the composition of the sample. The data were processed using AZtec software, and elemental identification was performed based on the characteristic X-ray peaks detected in the spectrum. To investigate the crystalline structure, size, and chemical composition of the RGO on the SPGE, the surface was carefully cut to expose the working electrode to analyse the electrode\u0026rsquo;s active area where the deposition of RGO occur. The sample was analysed using XRD with a PANalytical X'pert PRO system (45 kV, 40 mA), scanned over a 2θ range of 5\u0026deg; to 90\u0026deg; at a scanning rate of 2\u0026deg;/min.\u003c/p\u003e \u003cp\u003eRaman spectroscopy was performed using NTEGRA SPECTRA MT MDT system with a laser excitation wavelength of 514 nm to analyse the vibrational modes and structural properties of RGO. This method provided the information on the D (~\u0026thinsp;1350 cm\u003csup\u003e-1\u003c/sup\u003e), G (~\u0026thinsp;1580 cm\u003csup\u003e-1\u003c/sup\u003e) and 2D (~\u0026thinsp;2700 cm\u003csup\u003e-1\u003c/sup\u003e) bands, which are associated with the degree of graphitization, defect density and layer structure. The D band corresponded to the structural defects and disorder while the G band indicated the sp\u003csup\u003e2\u003c/sup\u003e graphitic domains. The 2D band (~\u0026thinsp;2694 cm⁻\u0026sup1;), a second-order overtone of the D band, is due to a two-phonon scattering process at the K point of the Brillouin zone. Its intensity and shape reveal information about the number of graphene layers and their stacking order[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The intensity ratio (ID/IG) which indicate the defect density and degree of reduction was analysed to obtain the optimize synthesis condition.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Electrochemical detection of dopamine\u003c/h2\u003e \u003cp\u003eThe electrochemical detection of dopamine was optimised at several pH (5.0, 6.0, 7.4, 8.0, 9.0). The optimum pH for the dopamine detection was analysed using cyclic voltammetry (CV). The cyclic voltammetry (CV) and square wave voltammetry (SWV) were employed to evaluate the electrode's response to dopamine. For CV, measurements were taken from a potential range of -0.3 V to +\u0026thinsp;0.8 V at a scan rate of 50 mVs\u003csup\u003e-1\u003c/sup\u003e. SWV measurements involved a positive potential sweep from \u0026minus;\u0026thinsp;0.2 V to +\u0026thinsp;0.4 V, with a step potential of 10 mV, a pulse amplitude of 15 mV, and a frequency of 10 Hz. Electrochemical impedance spectroscopy (EIS) was performed at the open circuit potential (OCP), between 0.044 V to 0.010 V depend on the dopamine concentration. The frequency range used for EIS measurements was from 100 kHz to 100 mHz, with a sinusoidal amplitude of 10 mV. Conducting EIS at the OCP allowed for the characterization of the natural electrode-electrolyte interface without the influence of external potential perturbations, offering valuable insights into the equilibrium interactions of dopamine with the electrode surface, such as adsorption and double-layer effects.\u003c/p\u003e \u003c/div\u003e"},{"header":"3.0 Results and Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Surface characterization of RGO modified electrode surface.\u003c/h2\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1 Effect of Graphene Oxide (GO) concentration towards RGO formation.\u003c/h2\u003e \u003cp\u003eThe advancement of high-performance electrochemical sensors requires the optimisation of sensing electrode materials. This research aims to enhance the optical and electrical properties of RGO on screen-printed gold electrodes (SPGEs) \u003cem\u003evia\u003c/em\u003e the regulated electrodeposition technique. To attain optimal RGO deposition, the concentration of the GO solution and the temperature of the water bath were methodically altered.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents a morphological analysis, showcasing FESEM images of electrodeposited reduced graphene oxide (RGO) on a screen-printed gold electrode (SPGE) at different concentrations of graphene oxide (GO) solution. The findings indicate a substantial link between the concentration of GO and the synthesis of RGO on SPGE. All FESEM images exhibited a consistent morphology, with RGO forming in the interstices between the gold nanostructures on the SPGE, achieved through direct adhesion to the gold surfaces under all experimental circumstances. At the minimal concentration of 333 mgmL⁻1, initial RGO production was detected within the interstices of the gold nanostructures. As the concentration increased to 500 mg mL⁻1, the coverage of RGO extended, resulting in a more significant presence on the electrode surface. Increasing the concentration to 667 mgmL⁻1 achieved total surface coverage, along with the formation of holes and ripples that signify RGO aggregation[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA thorough grasp of the material composition is essential to confirm the presence of carbon (C) in RGO. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents essential elemental data, providing a detailed quantitative analysis of atomic percentages and the C:O ratio, which is crucial for RGO characterization. An analysis of the C:O ratio indicates an improvement following RGO electrodeposition across all concentrations, except for the lowest ratio. The C:O ratio for GO powder was determined to be 401, whereas the values for RGO at concentrations of 333 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, 500 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, and 667 mgmL⁻\u003csup\u003e1\u003c/sup\u003e were found to be 2.34, 12.56 and 4.97 respectively. except for the 333 mgmL⁻\u003csup\u003e1\u003c/sup\u003e sample, the other samples showed a diminished presence of functional groups in comparison to GO powder. This is due to the fact that during the electrodeposition process, the quantity of GO available for deposition was lower in comparison to the other concentrations (500 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, 667 mgmL⁻\u003csup\u003e1\u003c/sup\u003e). Consequently, at a concentration of 333 mgmL⁻1, the electrodeposited reduced graphene oxide (RGO) fails to sufficiently develop and occupy the gap on the surface of the screen-printed graphite electrode (SPGE). The results obtained were consistent with the FESEM results presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The electrodeposited RGO exhibits structural properties that are intermediate between those of graphene oxide and graphene. This is because RGO has been only partially removed of its oxygen functional groups and is left with structural imperfections that do not allow it to attain the ideal structure of graphene[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of EDS analysis for different GO solution concentration\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConcentration (mgmL⁻\u003csup\u003e1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCarbon (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOxygen (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eC:O Ratio\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e333\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e43.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e12.56\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e667\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e51.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.97\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eX-ray diffraction (XRD) was employed to investigate the modifications in interlayer spacing within graphene-related materials of the fabricated electrode. Although reduced graphene oxide (RGO) and graphene oxide (GO) are both composed of carbon atoms, the XRD patterns reveal distinct differences due to variations in atomic arrangement. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a) presents the XRD patterns for GO powder and RGO at different electrodeposition concentrations. The GO powder exhibits a characteristics diffraction peak at 2θ\u0026thinsp;=\u0026thinsp;11.47\u0026deg;, which is attributed to its oxidized structure with a high degree of interlayer spacing caused by oxygen functional groups and water intercalation[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. As a result of electrodeposition of RGO, this GO peak completely diminishes which confirm the removal of oxygen-containing functional groups and structural formation of RGO.\u003c/p\u003e \u003cp\u003eAt the same time, the broad peak at 2θ\u0026thinsp;=\u0026thinsp;22.8\u0026deg;, (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b)) which are already present in GO, remains in RGO. The peak which corresponds to the (002) plane of a graphene-like structure shows a decrease in the interlayer spacing due to the removal of some oxygen containing functional groups indicating the reestablishment of sp2 network on reduction. The broad peak may be due to RGO retains some structural disorder and does not achieve complete graphitization[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. In contrast, the XRD pattern of gold, a crystalline material, showed well-defined peaks at 2θ\u0026thinsp;=\u0026thinsp;38.38\u0026deg;, 44.62\u0026deg;, 64.88\u0026deg;, 77.97\u0026deg;, and 82.19\u0026deg;, corresponding to the (111), (200), (220), (311), and (222) planes of the gold nanostructure [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. These peaks confirm its crystalline nature, which serves as a conductive platform for RGO deposition.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eRaman spectroscopy was employed to analyse the structural properties of RGO electrodeposited at varying concentrations (333 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, 500 mgmL⁻\u003csup\u003e1\u003c/sup\u003e and 667 mgmL⁻\u003csup\u003e1\u003c/sup\u003e). The Raman spectra is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e highlighting the D (~\u0026thinsp;1350 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and G (~\u0026thinsp;1580 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) bands which are the indications of the structural defects and graphitic domains, respectively. Intensity ratio (I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e) is the important parameter for the assessment of the defect density. The intensity ratio was calculated and tabulated in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. At 333 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, the I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e ratio was 1.38, which is the lowest compared to 500 and 667 mgmL⁻\u003csup\u003e1\u003c/sup\u003e. This is because at low concentration, the GO sheets available may be less for deposition process which results in a thinner RGO layer with fewer defects. The thin RGO layer may have a larger and more continuous sp\u003csup\u003e2\u003c/sup\u003e domains with less structural defects which explains the low I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e ratio.\u003c/p\u003e \u003cp\u003eHowever, at 500 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, the I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e ratio increased to 1.72, which is higher than at 333 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, indicating better exfoliation of GO during the reduction process. This led to a decrease in the average size of sp\u0026sup2; domains and the introduction of more structural defects. In addition, the increase in structural defects indicates that the number of active sites on RGO has increased, leading to better conductivity of the RGO film [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e ratio for 667 mgmL⁻\u003csup\u003e1\u003c/sup\u003e shows a slight decrease from 1.72 (at 500 mgmL⁻\u003csup\u003e1\u003c/sup\u003e) to 1.62, indicating that at higher GO concentrations, the electrodeposition process forms a thicker RGO layer. This increased thickness may lead to agglomeration, where defects become distributed within the bulk material rather than remaining on the surface. As a result, fewer defects are detected at the surface, leading to a lower D-band intensity in Raman analysis [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. This trend is consistent with FESEM images, which show increased film thickness and possible sheet stacking at higher GO concentrations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRaman spectra analysis of I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e for different concentration of Graphene Oxide (GO) solution 333 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, 500 mgmL⁻\u003csup\u003e1\u003c/sup\u003e, 667 mgmL⁻\u003csup\u003e1\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConcentration (mgmL⁻\u003csup\u003e1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eG\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eI\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e333\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e182844.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e132332.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.38\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e134635.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e78073.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e667\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e107109.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e66163.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.62\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2 Effect of electrodeposition temperature on RGO formation.\u003c/h2\u003e \u003cp\u003eThe prior characterisation results indicate that the ideal concentration for the synthesis of reduced graphene oxide (RGO) is 500 mg/mL. This concentration appears to facilitate the reduction process, resulting in a more distinct RGO structure relative to other concentrations. Consequent to this discovery, a concentration of 500 mg mL⁻\u0026sup1; of GO was selected for subsequent investigations pertaining to temperature. Through the analysis of temperature's effect on the properties of RGO at its optimal concentration, a deeper comprehension of RGO's thermal stability and structural integrity can be gained, both of which are vital for its prospective applications.\u003c/p\u003e \u003cp\u003eFESEM was used to analyse the morphology of RGO electrodeposited on screen-printed gold electrodes (SPGE) at various temperatures. The images in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e illustrate the relationship between deposition temperature and RGO formation. The RGO deposits both within the interstices and on the surface of the SPGE, bonding directly to the gold surfaces under all experimental conditions, similar to what was observed in the concentration variation analysis. There is a strong correlation between deposition temperature and the density of RGO formation on SPGE. FESEM analysis indicates that as the electrodeposition temperature increases, the amount of RGO deposited on the SPGE surface also rises. At 40\u0026deg;C, RGO formation is evident within the gaps of the gold nanostructures. By 60\u0026deg;C, the RGO density increases, covering a significant portion of the gold surface. However, despite the higher density, the RGO does not completely fill the gaps, suggesting that at elevated temperatures, the reduction process occurs more rapidly, potentially leading to less uniform deposition. This highlights the importance of optimizing deposition temperature for achieving a well-structured RGO layer.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents the elemental composition of RGO deposited at different temperatures which are 40\u0026deg;C, 50\u0026deg;C, and 60\u0026deg;C. The table highlight the variations in carbon and oxygen content, as well as the corresponding carbon-to-oxygen (C:O) ratio. The results shows that the reduction temperature significantly influences the chemical structure of RGO formation. At 40\u0026deg;C, the RGO shows the highest carbon content which is 50.35% and the lowest oxygen content at 4.01% which displays a high C:O ratio at 12.56. The high C:O ratio indicate an efficient reduction process with a well-preserved graphene structure and significant elimination of oxygen-functional groups [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHowever, at 50\u0026deg;C, the lowest C:O ratio of 2.47 was obtained with a decrease in carbon content from 50.35\u0026ndash;32.76% while an increase in oxygen content to from 4.01 to 13.3%. This suggests that reduction was less successful at 50\u0026deg;C, which might be due to oxygen-trapped defects formed or because oxygen functional groups were not completely removed. As the temperature of the water bath was increased to 60\u0026deg;C, both carbon and oxygen content increased to 49.07% and 11.52% respectively which leads to higher C:O ratio of 4.26 in comparison to 50\u0026deg;C which shows that the removal of oxygen content in 60\u0026deg;C is better than 50\u0026deg;C. Nevertheless, the reduction process's efficiency did not rise in proportion to temperature. This could be because at higher temperature, the competing effects occurs such as defects formation, structural re-oxidation or an altered reduction kinetics[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of EDS analysis for different temperature.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTemperature\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCarbon (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOxygen (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eC:O Ratio\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e40\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e12.56\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e50\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e32.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e13.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.47\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e60\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e49.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e11.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.26\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe diffraction pattern of GO and RGO treated at different temperatures is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. Diffraction pattern of GO has two diffraction peaks at 11.47 (001) as the characteristic peak and 22. (002) [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The diffraction pattern of RGO shows no characteristics peak of GO at 11.47. This is due to the removal of oxygen functional groups such as hydroxyl and carboxylate which indicate the structural changes from GO to RGO with a reduction in basal spacing. The diffraction peak of RGO appear at 22.6\u0026deg; which confirm the successful reduction process. The peak broadening of all RGO samples indicates a structural disorder and small graphitic domains. Diffraction patterns of all samples are similar, but different reduction temperatures may affect the extent of graphitization and defect density.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e presents the Raman spectra of RGO subjected to treatment at different temperatures ranging from 40\u0026deg;C to 60\u0026deg;C. The three prominent peaks, specifically the D, G, and 2D bands, are situated at 1350 cm⁻\u0026sup1;, 1580 cm⁻\u0026sup1;, and 2694 cm⁻\u0026sup1;, correspondingly. The Raman spectra were utilised to conduct a qualitative analysis of the extent of imperfections in the graphitic lattice as displayed in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The intensity of the D peaks, which represents the vibrations of sp\u0026sup3;-hybridized carbon atoms in disordered graphene, decreased as the temperature increased. This reduction indicates that at elevated temperatures, a substantial portion of the imperfections in the graphene material had been rectified[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. This is due to the removal of oxygen-containing functional groups which restores sp2 hybridized carbon domains that lead to improve the structural order [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. The simultaneous decline in the G peaks indicates the alterations in the structure and the decrease in the size of the sp\u003csup\u003e2\u003c/sup\u003e domain. Nevertheless, it is evident that the strength of G peaks diminishes as the temperature rises. This suggests that elevated temperatures can facilitate the generation of imperfections in the graphene lattice. Furthermore, the I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e ratio exhibited little changes, indicating that the ratio of sp\u003csup\u003e2\u003c/sup\u003e and sp\u003csup\u003e3\u003c/sup\u003e hybridised carbon atoms was not significantly influenced by the rise in temperature. These findings indicate that although the overall structural strength of the sample decreases as temperatures rise, the basic graphitic character of the material remains intact.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eQuantitative analysis of Raman spectra of I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e for different water bath temperature of 40\u0026deg;C, 50\u0026deg;C, 60\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTemperature (˚C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eG\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eI\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e134635.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e78073.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e99661.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60812.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.64\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e90319.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e55285.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.63\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Electrochemical sensing of dopamine\u003c/h2\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1 Effect of RGO/SPGE on Dopamine detection.\u003c/h2\u003e \u003cp\u003eCyclic voltammetry (CV) was utilized to investigate the electrochemical behavior of electrodeposited reduced graphene oxide (RGO) on SPGE. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a) illustrates the electrochemical characteristics of SPGE and RGO/SPGE in deionized water and phosphate-buffered saline (PBS). In deionized water, both SPGE and RGO/SPGE demonstrate the absence of redox reactions, as no redox peaks are detected on the CV curve. Nevertheless, the higher electroactive surface area of the RGO/SPGE results in a more extensive CV plot, which is ascribed to its enhanced capacitive current [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. In PBS (pH 7.4), the CV curve of SPGE shows a reduction peak in the absence of dopamine. This is due to the behavior of the gold surface. The SPGE may display reduction peaks in phosphate buffer as a result of surface interactions between phosphate ions and the gold electrode. This interaction may entail the adsorption of phosphate molecules, succeeded by electron transfer processes at the gold surface, leading to discernible peaks in the CV curve. This suggests that the reduction peak detected in bare SPGE was probably attributable to the redox-active characteristics of the gold surface in phosphate buffer [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. The CV curve of RGO/SPGE in PBS exhibits an enhancement in reduction current relative to SPGE, along with the emergence of an oxidation peak. This results from the augmentation of electroactive surface area and enhanced electron transfer kinetics attributable to the presence of the RGO layer. The presence of RGO enhances the electrode's conductivity and increases the number of active sites, leading to a greater current response. The oxidation peak may result from residual oxygen-containing functional groups on RGO or interfacial phenomena at the electrode surface [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn the presence of 1mM dopamine in PBS (pH 7.4), Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b) SPGE and RGO/SPGE exhibited redox peaks which correspond to the oxidation of dopamine to dopamine-quinone and its subsequent reduction. In comparison to SPGE, the RGO/SPGE showed more well-defined redox peaks and significantly higher peak currents. This indicates that the presence of RGO enhanced the electrochemical response towards dopamine due to the high surface area, good electrical conductivity, and efficient π\u0026ndash;π interactions between its sp\u0026sup2; carbon domains and the dopamine's aromatic ring improved the electrochemical response to dopamine. These properties of RGO provided faster electron transfer and increased the number of electroactive sites available for dopamine detection[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe FTIR analysis was performed to study the chemical structure and functional groups in GO, SPGE, RGO/SPGE, dopamine as well as the interaction between dopamine and RGO/SPGE after electrochemical testing as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The FTIR spectrum of GO shows several characteristic peaks which confirms its oxygenated structure. The peak appears at 1040, 1250, 1376, 1610, 1707 and 3227 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e which are attributed to C\u0026ndash;O stretching, C\u0026ndash;O stretching, O\u0026ndash;H bending, C\u0026thinsp;=\u0026thinsp;C aromatic stretching, C\u0026thinsp;=\u0026thinsp;O stretching, and O\u0026ndash;H stretching respectively[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e], [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. For bare SPGE, the previous study reported the absence of the characteristic peaks in the FTIR spectrum due to its inert surface. However, in this work, the peaks were observed at 1121, 1376, 1654 and 1787 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. These peaks were more likely due to impurities[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] and instrumental noise[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe FTIR spectrum of RGO/SPGE shows significant change after the reduction of GO. The appearance of peaks at 999, 1303, 1596, 1704, 2341, 2599 and 3100 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e shows structural changes of GO. The disappearance of the peak at 1376 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e which correspond to O-H bending and the reduction of peak at 1250 and 1707 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e further confirms the successful reduction of GO. The peak observed at 1610 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in GO which is attributed to C\u0026thinsp;=\u0026thinsp;C stretching of sp2 hybridized carbon, shift slightly to 1596 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in RGO/SPGE. The shift confirms the restoration of the conjugated sp\u003csup\u003e2\u003c/sup\u003e-hybridized carbon domain during the reduction process. Furthermore, the broad peak at 3227 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in GO, corresponding to O-H stretching, shifts and weakens to 3100 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, indicating the decrease in hydroxyl group after the reduction of GO[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e], [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. Furthermore, the chemical structure and functional groups after electrochemical testing with dopamine was also being studied using FTIR analysis. The RGO/SPGE spectrums first showed distinctive peaks at 999, 1303, 1596, 1704, 2341, 2599 and 3100 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which corresponded to functional groups that included oxygen functional groups such as C-O, C\u0026thinsp;=\u0026thinsp;C, C\u0026thinsp;=\u0026thinsp;O and O-H. After dopamine testing, only a single peak remained at 999 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e which shows the alteration of the RGO/SPGE surface. The disappearance of peak at 1704 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026thinsp;=\u0026thinsp;O), 1596 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026thinsp;=\u0026thinsp;C) and 3100 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (O-H) aligned with previous study that shows the structural changes due to the dopamine reacting with the functional groups of RGO/SPGE surface. The remaining peak at 999 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e may indicate a shift in C-O stretching or a new vibrational environment resulting from the dopamine interaction[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. These FTIR results are consistent with the CV findings where a significant current response was observed which indicate the electrochemical interaction between dopamine and the RGO/SPGE surface.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2 The effect of pH on Phosphate Buffer Solution (PBS).\u003c/h2\u003e \u003cp\u003eCyclic voltammetry (CV) was employed to investigate the effect of pH on the electrochemical behaviour of reduced graphene oxide modified screen-printed gold electrodes (RGO/SPGE) in dopamine (DA) sensing. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, CV plots were obtained for RGO/SPGE in a 1 mM DA solution throughout a pH range from 5.0 to 9.0. Each pH value produced distinct oxidation peak currents (I\u003csub\u003epa\u003c/sub\u003e) and oxidation peak potentials (E\u003csub\u003epa\u003c/sub\u003e), indicating that the electrochemical response of DA is strongly dependent on pH. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the variation of I\u003csub\u003epa\u003c/sub\u003e and E\u003csub\u003epa\u003c/sub\u003e with pH. From the data shown in curve (a) of Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, it is clear that Ipa increased from 19.960 \u0026micro;A at pH 5.0 to a maximum of 30.025 \u0026micro;A at pH 7.4, before decreasing back to 18.867 \u0026micro;A at pH 9.0. Thus, it can be inferred that maximum dopamine oxidation takes place at pH 7.4. This condition can be best explained by the possible equilibrium between protonation of dopamine and surface interaction with the electrode leading to better electron transfer. Consequently, pH 7.4 was chosen to serve as the supporting electrolyte in further electrochemical studies. Moreover, curve (b) in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows that E\u003csub\u003epa\u003c/sub\u003e decreases with increasing pH, demonstrating a linear trend. The linear relationship between E\u003csub\u003epa\u003c/sub\u003e and pH is represented by the regression equation E\u003csub\u003epa\u003c/sub\u003e = 0.614\u0026ndash;0.054 pH, with a correlation coefficient of R\u0026sup2; = 0.9945, which indicates a strong correlation between the oxidation peak potential and pH. The slope of -0.054 V/pH is close to the theoretical Nernstian value of -0.059 V/pH which indicates that the dopamine oxidation process at RGO/SPGE involves an equal number of protons and electrons. This finding confirms that the redox mechanism of dopamine on RGO/SPGE follows a well-established electrochemical principle[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe detection of dopamine (DA) on RGO/SPGE operates through a specific mechanism. In a phosphate buffer solution (PBS) with pH 7.4, most of the dopamine exists in a protonated state (DAH+) which significate that the molecule carries a positive charge. Due to the aromatic nature of the molecule, it is capable of associating with the π-electron rich area of RGO by virtue of the π-π stacking. At the same time, the electropositive nature of dopamine facilitates electrostatic attractions to the negatively charged oxygen-containing groups of the RGO. The resulting combination of these interactions promotes the adsorption of dopamine on the membrane\u0026rsquo;s surface which in turn enhances the ease of electron transfer. During this process, dopamine undergoes oxidation to dopamine-quinone, which generates a measurable current, enabling the detection of dopamine with high accuracy [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e], [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. The mechanism of dopamine detection was shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on the CV plot of dopamine from Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, the oxidation peak of dopamine was observed to appear in between potential of 0.1 to 0.2 V. The analytical signals obtained from the CV plot was used as a reference for the determination of dopamine. The electrochemical detection of dopamine with RGO/SPGE was examined in PBS containing dopamine at different concentrations starts from 0.003\u0026ndash;0.05 mM using square-wave voltammetry (SWV) method in the potential region from \u0026minus;\u0026thinsp;0.2 to 0.4 V. As observed from Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e(a), as the dopamine concentration increases, the peak current also rises, and a distinct oxidation peak near 0.1 V becomes sharper and more intense at higher concentrations which confirm the RGO/SPGE\u0026rsquo;s excellent electrocatalytic activity for dopamine oxidation. As shown in the derived Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e(b), the peak current (I\u003csub\u003ep\u003c/sub\u003e) is linearly depended on the concentration of dopamine with a regression equation of I\u003csub\u003ep\u003c/sub\u003e (\u0026micro;A)\u0026thinsp;=\u0026thinsp;56.274 [Dopamine]\u0026thinsp;+\u0026thinsp;0.1231 with high correlation coefficient (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.9765). The sensitivity of RGO/SPGE was found to be 511.58 \u0026micro;A mM⁻\u0026sup1;cm⁻\u0026sup2;. The limit of detection (LOD) is defined as LOD\u0026thinsp;=\u0026thinsp;3S\u003csub\u003eB\u003c/sub\u003e/b, where S\u003csub\u003eB\u003c/sub\u003e is the standard deviation for the blank signal and b is the slope of the linear regression equation. S\u003csub\u003eB\u003c/sub\u003e was calculated by 3 repetitive experiments in blank PBS which resulted with the LOD of 1.2 \u0026micro;M.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e presents a comparative analysis of the sensitivity of the dopamine sensor developed in this study against those reported in recent literature. The RGO/SPGE sensor fabricated in this work shows a remarkable sensitivity of 511.58 \u0026micro;A mM⁻\u0026sup1;cm⁻\u0026sup2; which is notably higher compared to the previously reported graphene-based and composite sensor. The enhanced performance indicates the effectiveness of the electrodeposited RGO on SPGE in increasing the electrochemical response towards dopamine which make it as a highly competitive platform for sensitive dopamine detection.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of sensitivity performance between this work and previously published dopamine sensors.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStructure\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDetection method\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLinear range (mM)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSensitivity (\u0026micro;A mM⁻\u0026sup1;cm⁻\u0026sup2;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLOD\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eReferences\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRGO-AuNPs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSquare-wave voltammetry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.0001\u0026ndash;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.075\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRGO-PtNPs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSquare-wave voltammetry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.0001\u0026ndash;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.062\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZIF-67/rGO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAmperometry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.00025\u0026ndash;0.06625\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e93.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.052\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZnO/CuO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAmperometry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.001\u0026ndash;8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e90.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMIL-101(Cr)-SO\u003csub\u003e3\u003c/sub\u003eH/PEI-rGO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAmperometry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.00025\u0026ndash;0.23875\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e327.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePVA-ZnO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCyclic voltammetry (CV)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.1\u0026ndash;0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e120.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGa2O3\u0026sdot;ZnO@SWCNT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAmperometry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.001\u0026ndash;4.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e253.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.052\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIn2O3\u0026sdot;ZnO@MC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAmperometry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.0005\u0026ndash;2.056\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e215.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.024\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCuNi-MOF@rGO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAmperometry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.001\u0026ndash;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRGO/SPGE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSquare-wave voltammetry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.003\u0026ndash;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e511.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eThis work\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.1.3 EIS Analysis of RGO/SPGE in in Dopamine Detection.\u003c/h2\u003e \u003cp\u003eElectrochemical impedance spectroscopy (EIS) is a crucial technique to investigate the interaction mechanisms between dopamine (DA) concentrations and electrode surfaces. This method provides comprehensive insights into fundamentals processes, including electron transfer kinetics, mass transport via diffusion, and surface phenomena such as adsorption. In addition, EIS allows the assessment of the electrical conductivity of the sensor which make it as an effective technique for characterizing the complex electrochemical behaviour of DA detection and analysis. The Nyquist plot for the electrochemical oxidation of DA shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e(a) displayed the characteristics behaviour of the oxidation process, featuring two distinct semicircles. The Nyquist plot was fitted and analysed using the equivalent circuit model as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e(b). The circuit comprises key elements such as solution resistance (R\u003csub\u003es\u003c/sub\u003e), film resistance (R\u003csub\u003e1\u003c/sub\u003e) and charge transfer resistance (R\u003csub\u003e2\u003c/sub\u003e)[\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e]. The parameters obtained from the fitted Nyquist plot was tabulated in Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The decreases in the charge transfer resistance values as the concentrations of DA increases were proved by the reduction of the second semicircles in the Nyquist plot. This phenomenon was caused by the increase in the availability of the electroactive dopamine molecules which facilitates the redox reaction. When the availability of the electroactive dopamine molecules increases, the electron transfer kinetics on the electrode surface increase which causing the resistance value decreases. The charge transfer resistance value was also plotted against the concentration of DA. The calibration plot shows a strong inverse linear relationship between the charge transfer resistance and DA concentrations which was indicated by the high regression coefficient (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.9896). The regression value shows the RGO/SPGE ability to accurately detect and quantify DA based on its impact on charge transfer kinetics. The results obtained from SWV and EIS align closely which revealed a strong relationship between current response and charge transfer resistance. The increase in peak current observed in SWV is directly correlated with the charge transfer resistance from the EIS results. As the charge transfer resistance decreases, the electron transfer kinetics improves which is reflected in the higher current response shown in the SWV results.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSolution Resistance (Rs), Film Resistance (R1), Charge transfer Resistance (R2) and Constant Phase Element (CPE) value obtained from the Nyquist Plot and equivalent circuit model.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConcentrations (mM)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRs (Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eR1(Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eR2 (Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCPE (Ω\u003csup\u003e-1\u003c/sup\u003ems\u003csup\u003en\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.003\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.588\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1503.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e829710\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e7.2326\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.006\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.574\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1175.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e732800\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.494\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.641\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2346.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e703790\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e6.2566\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.814\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2975.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e668590\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.9844\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.015\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.750\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3525.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e525000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.8612\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.613\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2966.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e264580\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.0273\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.850\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3423.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e242530\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.9747\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e3.1.4 Interference study\u003c/h2\u003e \u003cp\u003eSelectivity is a crucial analytical parameter, particularly for electrochemical sensors designed to operate in complex biological samples where interference from coexisting species can significantly affect detection accuracy. In the case of dopamine (DA) detection, challenges arise due to the overlapping oxidation potentials of common interferences like uric acid (UA) and ascorbic acid (AA), which are often present in higher concentrations in biological fluids[\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e]. This interference can compromise sensor performance, making selectivity evaluation essential. To assess the selectivity of the RGO/SPGE sensor, individual voltammograms of DA (0.07mM), UA (0.4mM), and AA (1mM) were recorded, along with the voltammogram of their mixture, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e. The results reveal that DA and UA exhibit distinct and well-defined oxidation peaks at 0.17 V and 0.31 V respectively, while AA presents a broad, indistinct peak lacking a sharp maximum at 0.14 V. In the mixture, the peak current of DA remains unaffected by the presence of UA and AA, as indicated by the consistent peak height of DA. Even at the same potential as AA, the peak current of dopamine shows no significant change. This behaviour may be attributed to an interaction between the amino group of the DA molecule and the sensor surface, which likely inhibits the oxidation of AA. These results demonstrate the ability of the RGO/SPGE sensor to effectively differentiate DA from other analytes, highlighting its high level of selectivity. Such performance is particularly valuable in complex matrices where precise and independent detection of DA is essential.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.1.5 Stability, reproducibility and repeatability of RGO/SPGE\u003c/h2\u003e \u003cp\u003eThe reproducibility of the sensor is a crucial parameter in assessing the performance of electrochemical devices. To evaluate the reproducibility of the RGO/SPGE, successive square wave voltammetry (SWV) measurements were conducted using five different electrodes. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e(a), the response currents exhibited a relative standard deviation (RSD) of 4.04% (n\u0026thinsp;=\u0026thinsp;3), indicating the excellent reproducibility of the RGO/SPGE and confirming its reliability and consistency in electrochemical measurements.\u003c/p\u003e \u003cp\u003eThe stability of the RGO/SPGE was also assessed by storing it at room temperature for one week and measuring its current response to 0.07 mM DA solution, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e(b). After one week, 91.75% of the initial current response was retained, demonstrating the good stability of the developed sensor. These results highlight the potential of the RGO/SPGE for long-term applications, although further studies on extended storage durations and varying environmental conditions would provide a more comprehensive understanding of its shelf life. To improve longevity, electrodes may require storage in optimal conditions, such as an inert atmosphere, low temperature, low humidity, or vacuum.\u003c/p\u003e \u003cp\u003eIn addition, the RGO/SPGE was evaluated for repetitive analysis through 15 consecutive measurements of DA determination, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e(c). The calculated RSD of 3.28% (n\u0026thinsp;=\u0026thinsp;3) underscores the sensor's durability and consistent performance in repeated use. This impressive reproducibility and stability establish the RGO/SPGE as a reliable platform for electrochemical sensing, paving the way for its integration into practical applications, including real-time monitoring and clinical diagnostics.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4.0 Conclusion","content":"\u003cp\u003ePristine reduced graphene oxide (RGO) was effectively synthesised on a screen-printed gold electrode (SPGE) by an electrodeposition method, creating a highly efficient platform for dopamine detection. The optimisation of electrodeposition parameters, specifically the concentration of graphene oxide (GO) solution and the temperature of the water bath, indicated that optimal circumstances were a GO concentration of 0.5 mg/mL and a water bath temperature of 40\u0026deg;C. Under these optimised conditions, the RGO/SPGE sensor exhibited remarkable efficacy in dopamine detection via square-wave voltammetry (SWV), attaining a sensitivity of 511.58 \u0026micro;A mM⁻\u0026sup1;cm⁻\u0026sup2; and a detection limit of 1.2 \u0026micro;M. Electrochemical impedance spectroscopy (EIS) corroborated these findings by demonstrating a reduction in charge transfer resistance as dopamine content increased. The sensor demonstrated exceptional selectivity for dopamine, accurately differentiating it from prevalent interfering substances like uric acid and ascorbic acid. The RGO/SPGE sensor demonstrated remarkable stability, reproducibility, and repeatability, as indicated by consistently low relative standard deviation (RSD) values throughout all experiments. The results underscore the developed sensor's promise as a dependable, swift, and sensitive instrument for dopamine detection, presenting intriguing applications in clinical diagnostics and biochemical analysis.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThe authors express their gratitude for the support received from the Ministry of Higher Education Malaysia through the Fundamental Research Grant Scheme: 600-RMC/FRGS 5/3 (082/2023).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eHaziq wrote the main manuscript, Zaini, Sabirin and Maizatul are the supervisor involve in conceptualization and methodology, Norhazlin dan Zam involve in result analysis, Rozina and Fitrah involve validation and resources and Sabirin is the project administration. All authors reviewed the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eS. 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Pruneanu et al., The influence of uric and ascorbic acid on the electrochemical detection of dopamine using graphene-modified electrodes. Electrochim. Acta. \u003cb\u003e154\u003c/b\u003e, 197\u0026ndash;204 (Feb. 2015). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.electacta.2014.12.046\u003c/span\u003e\u003cspan address=\"10.1016/j.electacta.2014.12.046\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"biomedical-materials-and-devices","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Biomedical Materials \u0026 Devices](https://link.springer.com/journal/44174)","snPcode":"44174","submissionUrl":"https://submission.springernature.com/new-submission/44174/3","title":"Biomedical Materials \u0026 Devices","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Reduced Graphene Oxide (RGO), Screen-printed Gold Electrode (SPGE), Square Wave Voltammetry (SWV), Electrochemical Impedance Spectroscopy (EIS), Dopamine (DA).","lastPublishedDoi":"10.21203/rs.3.rs-6704266/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6704266/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDopamine is a crucial neurotransmitter, and atypical amounts have been linked to various neurological disorders. Nonetheless, the precise and efficient detection of dopamine is impeded by interference from structurally analogous biomolecules such as uric acid and ascorbic acid. A pristine reduced graphene oxide (RGO) on screen-printed gold electrode (SPGE) has been successfully developed for the sensitive and selective detection of dopamine. Reduced graphene oxide (RGO) was synthesised via the electrodeposition method, with manufacturing conditions optimised by varying the concentration of graphene oxide (GO) and the temperature of the water bath. The ideal conditions were determined to be 500 mgmL⁻1 of GO and 40\u0026deg;C, attributed to the elevated C:O ratio of RGO on SPGE, leading to superior electrochemical performance. The optimised RGO/SPGE sensor was evaluated for dopamine detection via square-wave voltammetry (SWV). The findings suggest a high sensitivity of 446.83 \u0026micro;A mM⁻\u0026sup1;cm⁻\u0026sup2;, with a detection limit (LOD) of 1.2 \u0026micro;M, demonstrating its ability to identify low quantities of dopamine. FTIR analysis demonstrated a significant reduction of GO and the interaction between dopamine and the RGO-modified surface, corroborating the observed electrochemical changes. Electrochemical impedance spectroscopy (EIS) was employed to examine the interfacial charge transfer characteristics of the electrode at different dopamine concentrations. The reduction in charge transfer barrier with rising dopamine concentrations indicates enhanced electron transfer kinetics. The sensor exhibited significant selectivity for dopamine, distinguishing it from interfering substances such as uric acid (UA) and ascorbic acid (AA). Moreover, the sensor exhibited remarkable stability, retaining 91.75% of its initial current response. The sensor has exceptional reproducibility and repeatability, with RSD values of 4.04% and 3.28% (n\u0026thinsp;=\u0026thinsp;3), respectively. These findings underscore the optimised RGO/SPGE sensor's promise as a reliable and economical electrochemical sensing platform, particularly in biological matrices.\u003c/p\u003e","manuscriptTitle":"Highly Sensitive Dopamine Biochemical Sensor Employing Pristine Electrodeposited Reduced Graphene Oxide","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-28 06:06:10","doi":"10.21203/rs.3.rs-6704266/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"290164304348694640223158709137345769676","date":"2025-05-27T04:37:37+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"182941560530939638235035947797414848452","date":"2025-05-27T01:09:33+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-26T22:05:11+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-22T13:33:30+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-22T13:29:30+00:00","index":"","fulltext":""},{"type":"submitted","content":"Biomedical Materials \u0026 Devices","date":"2025-05-20T06:10:54+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"biomedical-materials-and-devices","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Biomedical Materials \u0026 Devices](https://link.springer.com/journal/44174)","snPcode":"44174","submissionUrl":"https://submission.springernature.com/new-submission/44174/3","title":"Biomedical Materials \u0026 Devices","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e925da0b-abd4-496a-9ef3-34b63102f92d","owner":[],"postedDate":"May 28th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-07-11T10:38:10+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-28 06:06:10","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6704266","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6704266","identity":"rs-6704266","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}