Low-Cost Laser for Affordable Graphene-Induced Microband Sensor Fabrication

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A. Ribeiro, Deissy J. Feria, Paula C. Falcoswki, Marcelo N. P. Carreño, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3788473/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Graphene microband electrodes were fabricated by direct laser writing on Kapton® polyimide tape utilizing a low-cost, blue laser (500 mW and 405 nm). The structural properties of the graphene were examined by Raman spectroscopy, and key features such as D, G, and 2D bands, and the presence of multilayer structures were revealed. Scanning electron microscopy (SEM) provided insights into the microband morphology, highlighting the 3D (foam-like) nature of the graphene microbands. Electrochemical experiments revealed cyclic voltammetry profiles that demonstrated radial diffusion dominance at low scan rates and Randles–Sevcik behavior at higher scan rates. Reproducibility and repeatability analyses confirmed the stability and consistency of these microband electrodes within individual devices. Scanning electrochemical microscopy (SECM) images revealed the electrochemical reactivity of the microbands. At a relatively low microband separation (200 µm), the produced material can be collected at the adjacent microband, which was confirmed via generator/collector experiments. Theoretical-experimental comparisons regarding the current measured for a single microband were performed, and the obtained results were in good agreement, with deviations attributed to the 3D morphology of the microbands. This research underscores the potential of these cost-effective and reproducible graphene microband electrodes for diverse applications in electrochemical sensing, and we present preliminary results on caffeic acid and paracetamol detection. Band microelectrodes graphene electrochemical sensors Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction Graphene-based electrochemical sensors are promising for detecting and measuring various chemical and biological substances [ 1 , 2 ]. The large surface area, exceptional electrical conductivity, and unique mechanical and chemical properties of graphene make it an excellent material for electrochemical sensors [ 3 ]. Such materials can be used to fabricate electrochemical electrodes with small dimensions, usually referred to as microelectrodes, which present several advantages compared to their counterparts of conventional sizes. These include enhanced mass transport because of radial diffusion at the surface edges, enabling increased current density and greater sensitivity to voltammetric and amperometric measurements. The small dimensions also contribute to minimizing the iR drop due to the decrease in the double-layer capacitance. Hence, measurements can be performed without supporting electrolytes or in highly resistive media. When fabricated in the overall nanometric or micrometric dimension, these devices can be used for measurements in biological systems with high spatial resolution without significant tissue damage. Microelectrodes with different geometries, including disc, cylindrical, and band designs, have been constructed [ 4 ]. This last geometry is interesting because one of the dimensions is on the micro or nanoscale range, but the other can be extended to the centimeter range. Microband electrodes and their arrays have been used in various fields, such as food processing and medical and environmental analysis [ 5 ]. As a microelectrode, the microband electrode also has increased sensitivity owing to the high mass transport rate originating from radial diffusion [ 6 – 8 ]. Band microelectrodes have been fabricated using different methods, mainly photolithography, screen printing, vacuum evaporation, and sputter deposition methods [ 9 – 11 ]. Because of the advantages mentioned above, these materials have attracted attention for electroanalytical applications, and several examples can be found in the literature [ 12 – 15 ]. The use of such devices in flowing systems has also been explored[ 16 – 18 ], as well as to obtain analytical [ 19 ] and kinetic [ 20 ] information in redox systems. The separation between two adjacent band microelectrodes and the influence of these two microelectrodes on the interaction of diffusion fields have been examined in several works [ 21 , 22 ]. Direct laser writing or laser-induced graphene (LIG) is a method [ 23 ] that allows the production of graphene, mostly 3D (foam-like), trails that can work as microband electrodes. The LIG process involves the use of different types of lasers (CO 2 , UV, and visible) with different wavelengths and powers to irradiate the surface of a substrate that contains carbon atoms, such as polydimethylsiloxane (PDMS) [ 24 ], polyimide (PI) [ 25 – 27 ], polyetherimide (PEI), polyethersulfone (PES), and a variety of other materials [ 28 , 29 ]. Through a photothermal process [ 30 ], the surface material absorbs laser light, causing local heating to temperatures from 800°C to more than 2500°C, depending on the laser type and power. This results in a sublimation process where bonds such as C-H, C-N, C = O, and C-O are broken, leading to the elimination of N, O, and other atoms as gaseous compounds, and the remaining carbon atoms are rearranged on the surface to form a graphene structure [ 31 ]. The overall method is relatively simple, with the irradiated sample kept under atmospheric conditions, with no need for vacuum, precursor gases, or external heat sources other than the laser itself. In this work, graphene microbands were fabricated by direct laser writing utilizing a low-cost, low-power blue laser (500 mW, 405 nm). The microband electrodes were patterned at room temperature on polyimide tape fixed to a glass slide. The graphene quality was studied mainly by Raman spectroscopy, electron microscopy, and electrical conductivity measurements. The devices were fully characterized by surface and electrochemical techniques, and encouraging results were achieved regarding analytical applications. The proposed method offers a simple and fast alternative approach that can be easily employed for mass-production electrochemical devices, and preliminary results on caffeic acid and paracetamol detection are shown. Experimental Device Construction The electrodes were fabricated utilizing Kapton® polyimide tape as a carbon precursor, approximately 100 µm thick, with silicone adhesive. This polymer was chosen due to its thermal stability up to 400°C and low thermal conductivity and because it leads to graphene films with very high electrical conductivity. The tape was fixed on a 2.5 cm × 2.5 cm glass slide previously cleaned with acetone and ethanol, not leaving air pockets when the tape adhered to the support. The conductive graphene pattern was obtained using a commercial laser diode driven by a computer-controlled XYZ positioning table. The electrode geometry templates were produced on AutoCAD® 2016 software and exported to the driving software that controls the XY scan velocity and direction. The laser beam has a wavelength centered at 405 nm, 500 mW power, and a focal spot size of approximately 180 µm. To obtain the optimal conditions, as determined in previous work [ 32 ], the glass/Kapton substrates were placed on a horizontal holder at a constant distance of 12.7 cm from the head of the laser. The scan was performed at a 250 mm/min writing speed in an ambient atmosphere. Eight linear devices were produced per slide, as shown in Fig. 1a. Afterwards, each device was isolated by cutting the slide into 1.3 × 0.6 cm 2 pieces (Fig. 1b). The device consists of two graphene bands of 10 mm in length and 150 µm in width. The separation between bands varied from 40 µm to 850 µm, and a device with 200 µm separation between adjacent microbands was employed in this work. Electrical contacts were established between a copper wire and graphene microbands utilizing conductive ink (Bare Conductive®), which consists of a combination of carbon black and graphite in a water-soluble solvent (Fig. 1c). To control the active area and protect the device, transparent epoxy resin (Araldite®) was deposited on the electrical contacts (Fig. 1d). After device construction, an electrochemical test was performed using ferricyanide as a redox probe in KCl medium, as described below (Fig. 1e). Finally, the electrical resistance of the microbands was measured through the two ends (Fig. 1c and 1f). Figure 1 Schematic illustration of the production and measurements of laser-induced graphene band microelectrodes. LIG characterization The structural and morphological characterization of the produced graphene trails was performed by optical microscopy, scanning electron microscopy (FESEM JEOL JSM-7401F), and confocal Raman spectroscopy (WITEC, Alpha300 R) using a green laser line (532 nm) and 30 mW of power. Spectra were acquired using 10x and 50x objective lenses. Raman mapping of the 2D band was performed in a rectangular area of 400 µm × 100 µm along the trail to evaluate the continuity and uniformity of the produced 3D graphene. Additionally, Raman spectra were taken at several points within that area. Each spectrum was an average of 10 acquisitions with 2 s of accumulation time per acquisition. The electrical conductivity of the graphene trails was measured before and after the electrochemical experiments to evaluate the eventual contamination or damage of the graphene trails with the tested chemical solution. For this purpose, the ends of the trails (Fig. 1f) were connected to a copper wire with conductive ink and then covered with a final insulating layer of epoxy. The I versus V curves were obtained by connecting the wires to a source measurement unit (Keysight SMU model B2902A). The electrical resistance was measured, and the sheet resistance of the produced graphene was estimated. Electrochemical Measurements All the electrochemical measurements were performed with a PGSTAT 128 potentiostat from Eco Chemie (Utrecht, Netherlands) using Nova control software for data acquisition. A 3-electrode system was used for most of the electrochemical measurements, with a Ag|AgCl (KCl sat) homemade reference electrode [ 33 ] and a platinum wire as the counter electrode. Scanning electrochemical microscopy (SECM) was performed with an SECM workstation from Sensolytics (Bochum, Germany). The Pt microelectrode (25 µm in diameter from Goodfellow (Huntington, England)) used in the SECM experiments was fabricated with a borosilicate glass micropipette pulled using P-97 equipment from Sutter Instrument (Novato, USA). The RG (RG = rg/r, where rg is the radius of the electrode along with the surrounding insulator and r is the radius of the Pt disc fiber) of the microelectrode was determined by fitting the approach curve to the theoretical curve (Fig. S1 ) using ferricyanide as a reversible electrochemical probe. The experiment was performed using polyimide tape as an insulating substrate, and the RG value was found to be approximately 12. All the solid chemicals used were of analytical grade and used without further purification. The solutions were prepared using deionized water processed on a purifying system from Nanopure Infinity (Barnstead, US). K 3 [Fe(CN) 6 ] and KCl were obtained from Sigma Aldrich (San Luis, USA). Cyclic voltammetry (CV) and SECM experiments were carried out in a 5 mM K 3 [Fe(CN) 6 ] + 1.0 M KCl solution. The CVs were recorded in a potential range comprising 0.6 to -0.2 V, and the SECM experiments were performed with the platinum microelectrode (tip) polarized at 0.1 V. The SECM images were obtained by scanning the tip in the x-y plane at a tip-substrate distance of 15 µm above the microbands. Results and Discussion Structural, Electrical, and Morphological Characterization The Raman spectra in Fig. 2 a show an optical image of the analyzed trail region, and the corresponding 2D band map is depicted in Fig. 2 b. Different intensity regions are observed in the mapping, and to understand the origin of these variations, Raman spectra were recorded at the spots marked A (more intense), B (medium intensity) and C (less intense) (Fig. 2 c and d). All the spectra present the typical D, G, and 2D bands for graphene. The D peak at ~ 1350 cm -1 is induced by defects and bent sp 2 carbon bonds, the G peak at ~ 1580 cm -1 (1st order allowed) is due to the stretching mode of sp 2 C-C bonds, and the 2D peak at ~ 2700 cm -1 (2nd order zone-boundary phonons) provides information on the approximate number of layers (or multilayer formation) based on its position, shape, intensity, and full width at half-maximum (FWHM). In Fig. 2 c, the spectra for spots A, B, and C are observed, and the difference in intensity can be appreciated. Figure 2 d shows the spectra normalized to the G band, allowing us to evaluate the relative intensities of the D, G, and 2D bands. As observed, the three spectra are very similar, indicating that all the mapped area is covered by graphene, varying from three to seven layers, as estimated from the I 2D /I G ratio. These results suggest that the observed variations in intensity are due to the nonplanar nature of the mapped trail surface, as shown in the SEM images in Fig. 3 , rather than to the nonuniform quality of the produced graphene. Figure 3 shows the top view of trails with the (a) maximum (~ 850 µm) and (b) minimum (~ 40 µm) band separations. Trails exhibiting a periodic sequence of bumps with different widths and heights can be observed, which is attributed to the nonuniform movement of the laser due to the utilized step motor. The cross-sections of the trails at different magnifications are shown in Fig. 3 c and 3 d, where the 3D and foam-like features of the obtained graphene are evident. In this way, as the Raman mapping is recorded while maintaining a constant focus, the focus is lost as different height points are analyzed, leading to the observed intensity changes. The average mapping spectrum was used to estimate the crystallite size (L a )[ 34 ], the distance between point defects (L d ), and the number of layers[ 35 , 36 ], leading to values of 8.9 nm for L a , 7.0 nm for L d and 3 to 7 for the number of graphene layers. The number of graphene defects on the polyimide can be attributed to the small graphene sheets that exhibit a structure similar to that of foam, as shown in the SEM images (Fig. 3 c and 3 d). The electrical conductivity measurements, performed on 10 electrodes before the electrochemical characterization, led to an average sheet resistance (R s ) of 32 ± 4 Ω/sq. In comparison, the R s value for 8 electrodes after electrochemical measurements was 32 ± 2 Ω/sq, following the best results reported in the literature for LIG graphene [ 37 ]; this is an indication that the electrochemical procedure induced no changes. Electrochemical characterization Preliminary experiments with the fabricated device involved recording a CV with one of the microbands in a solution containing ferricyanide, a chemical species with well-known reversible electrochemical behavior. At a relatively low scan rate (10 mV/s), a sigmoidal curve was obtained, as shown in Fig. 4 . At such an experimental long-term window (low scan rate), an almost steady-state type voltammetric profile is observed because the area of the diffusion layer becomes comparable to the smallest dimension of the microband after several seconds of electrolysis. However, it should be noted that for band microelectrodes, which possess a macroscopic dimension in the order of mm in length and the other (width) in the µm range, a true steady state is never reached [ 38 ]. On the other hand, at faster scan rates, the voltammetric profile becomes more peak-shaped because the size of the diffusion layer becomes less or comparable to the size of the microscopic domain. Consequently, a peak-shaped response is evident and is likely to follow the Randles–Sevcik equation. Fig. S2 shows CVs recorded with one microband at various scan rates, and typical peak-shaped curves can be observed. Again, at a relatively low scan rate, an almost sigmoidal-shaped CV characteristic of radial diffusion was obtained (red curve). An additional voltammetric experiment was performed to assess the response of each microband electrode and to investigate whether both microband electrodes could be interconnected. Fig. S3 shows the results, and it can be concluded that the voltammetric responses of both microbands are very similar, which is the first confirmation that the fabrication process yields electrodes with reproducible electrochemical profiles. The microband electrodes were then interconnected, and a new CV was recorded, generating the voltammetric red curve. The peak current obtained with the interconnected microbands was double that obtained with the individual microbands, confirming that the proposed method generates similar microbands. The reproducibility of a set of fabricated microband electrodes was explored by comparing cyclic voltammetric responses obtained using ferricyanide as a probe. Analysis of the voltammetric data revealed that the relative standard deviation was 13% (n = 10), and a repeatability value of 2.2% was found (n = 10) (Fig. S4). The repeatability test (Fig. S4B) yielded a relatively low value (2.2%), indicating that the same device exhibits high stability and consistency during repeated measurements. This result suggested that once a specific graphene microband electrode is fabricated, its electrochemical performance is reliably maintained over multiple measurements. This finding is encouraging because it demonstrates the potential for consistent and repeatable results within a single device, which is crucial for practical applications. The difference among devices must be related to minor geometrical variations inherent to the fabrication process. The stability of the devices is very good, and an automated process should improve the reproducibility. In summary, while the reproducibility of the devices may benefit from further optimization, the repeatability results indicate that individual devices exhibit excellent stability. The diffusional interaction between dual microelectrodes can be studied by changing the potential of one electrode (generator electrode) and detecting the products at the other electrode (collector electrode), whose potential is set to regenerate the starting material. A similar experiment was carried out with a fabricated device in which the distance between the two microbands was 200 µm. In this experiment, the potential of W1 was changed from an initial value to a final value, while the potential of the second electrode (WE2) was kept constant at 0.6 V, a potential value where the anodic oxidation of the species electrogenerated at the first electrode (WE1) is mass-transport controlled. The following equations (1 and 2) describe both processes: Figure 5 shows the CVs recorded at both WE1 and WE2. The measured collection efficiency (the ratio between the limiting current values at the collector and generator electrodes) was calculated as 24.2%, which is a relatively low value but determined by the considerable distance between both microelectrodes. This experimental outcome unequivocally validates the ability of the two microbands to act as separate and self-reliant electrodes (if required to operate independently), thereby substantiating their suitability for simultaneous and discriminating electrochemical sensing applications. The final characterization of the microband electrodes was performed by scanning electrochemical microscopy (SECM), a technique that offers valuable localized information on surface electrochemical reactivity with high resolution. A first investigation was conducted to assess the reactivity of the microband through approach curves. Ferricyanide was used as an electrochemical probe, and a Pt microelectrode, used as a tip, was used to carefully approach the microband surface (substrate). In this experiment, the potential of the tip is set at a value corresponding to the steady-state limiting current, i.e., the reduction of ferricyanide to ferrocyanide is mass-transport controlled. Ferrocyanide can reach the substrate and be electrochemically reduced, depending on the nature of the substrate. If the substrate is conductive, ferricyanide can be regenerated, and it diffuses back to the tip, causing the so-called SECM positive feedback. The extent of such an effect becomes more critical as the tip-to-substrate distance decreases. Figure 6 shows the approach curve obtained in this experiment (red curve), and the positive feedback confirms that the surface is electrochemically reactive. A parallel study was performed with an insulating substrate (Kapton), and as expected, the current decreased as the tip approached the substrate because of the hindered diffusion effect (negative feedback); i.e., ferricyanide was not regenerated at the substrate. Through SECM imaging, the conductivity of a surface can be assessed at high resolution, providing deeper insights into the electrochemical performance and quality of the fabricated microband electrodes. Figure 7 shows an SECM image of the device containing two microbands (WE1 and WE2) in a ferricyanide solution. Higher currents correspond to increased reactivity because of positive feedback. By inspecting the images, one can conclude that the reactivity is not homogeneous through the extension of a single microband, and some spots of higher reactivity are present in both microbands (blue and green). The other sections of the bands are seen in the yellow zones, which correspond to more reactive surfaces than insulating Kapton (orange regions). These results are consistent with the Raman mapping and SEM experiments (see Figs. 2 and 3 ) and suggest that the observed variations in reactivity or current are related to the 3D (foam-like) character of the graphene in the microbands. Therefore, integrating SECM with generator/collector experiments confirms the independence of microbands as separate electrodes and allows for a comprehensive characterization of their surface properties and conductivity distribution, revealing that the reactivity is not homogeneous within the microband. While such inhomogeneity of the active material on the microband restrains its use for kinetic studies, where the exact geometry of the electrodes and their homogeneity are critical factors for obtaining reliable results, the proposed method can still be used for other applications that do not depend on an electrode with rigorous homogeneous geometry. Mathematical Method for Current Calculations The experimental current (I exp ) was compared with the theoretical current (I theo ) for a microband electrode using Eq. (3) proposed by Szabo and coworkers [ 39 ]. This equation enables the calculation of the theoretical current for a microband electrode over the entire time range. \(\frac{{I(t)}}{{nFCDl}}=\frac{{\pi {e^{ - 2\sqrt {\pi \tau /5} }}}}{{4\sqrt {\pi \tau } }}+\frac{\pi }{{\ln [{{(64{e^{ - \Upsilon }}\tau )}^{1/2}}+{e^{5/3}}]}}\) Eq. 3 Where n is the number of electrons transferred, F is the Faraday constant, c is the bulk concentration of the reactant, D is the diffusion coefficient of the reactant, l is the length of the electrode, w is the width of the band electrode, t is the time, ϒ = 0.5772156, and τ = Dt/w 2 . SEM and optical microscopy images were obtained to confirm the length and width of the band electrode. The chronoamperograms obtained for 4 different microbands in the last section of the experiment (from 25 to 60 s) are presented in Fig. S5. Measurements were carried out at E = 0.1 V, an experimental condition in which the cathodic reduction of the electroactive species (ferricyanide) is diffusion controlled. The current was measured at t = 60 s, and the results are summarized in Table 1 . Table 1 Experimental and theoretical current values measured at 60 s for 4 microband electrodes. Device l (cm) w (cm) I exp (µA) I theo (µA) Deviation (%) 1 0.88 0.0155 4.72 4.29 9.0 2 0.88 0.0154 4.63 4.28 7.5 3 0.79 0.0157 4.88 3.99 20.6 4 0.82 0.0154 4.84 4.11 17.6 The deviation between the predicted and experimental results in Table 1 ranged from 7.5–20.6%, and the average value was calculated as 13%, which is surprisingly good considering that the utilized theoretical model is valid for coplanar electrodes and that the actual electrodes have a 3D structure, as demonstrated by the Raman and SEM results. Practical application Caffeic acid is an acid-derived phenolic compound usually found in green tea, coffee, fruits, and vegetables. Paracetamol, also known as acetaminophen, is another compound commonly used as an analgesic and antipyretic. Electrochemical sensors offer several benefits concerning quantification, such as high sensitivity and low cost. In this way, preliminary experiments were performed to evaluate the response of the proposed graphene microband electrodes for caffeic acid and paracetamol detection. Figures 8 a and 8 b show voltammograms recorded with the proposed microband in solutions containing caffeic acid (1 mM) and paracetamol (1 mM), respectively. These results confirm the reliability of the proposed device as a helpful platform for the inexpensive and straightforward detection of analytes at low concentrations. Conclusions The results presented in this study demonstrate that the graphene microband electrode device exhibits promising characteristics, making it a cost-effective and reproducible option for various applications. These considerations are based on two facts: the graphene quality and the low cost of the material production process. As shown, the produced material has a high electrical conductance (30 Ω/square) in a few layers (3 to 7) of graphene. The production process utilizes a low-cost (a few tens of dollars) and low-power blue diode laser. To our knowledge, this is the first study in which laser-induced graphene exhibiting the abovementioned properties was produced with this laser type. Considering its affordability and reproducibility, there is great potential for the widespread utilization and exploration of these devices in fields such as electrochemical sensing, energy storage, and beyond. Continued research and development efforts will uncover new opportunities and applications for this versatile graphene microband electrode device. Declarations Author Contribution L. M. A. R: Conceptualization, Methodology, Formal analysis, Writing - original draft, review and editing; and prepared figures 1, 4, 5, 8 and S2-S6D. J. 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Materials Research 19:1329–1334. https://doi.org/10.1590/1980-5373-mr-2016-0296 Qiao YC, Wei YH, Pang Y, Li YX, Wang DY, Li YT, Deng NQ, Wang XF, Zhang HN, Wang Q, Yang Z, Tao LQ, Tian H, Yang Y, Ren TL (2018) Graphene devices based on laser scribing technology. Jpn J Appl Phys 57:. https://doi.org/10.7567/JJAP.57.04FA01 J FD, Pinto ALM, Bertotti M, Carreno MNP, Pereyra I (2022) Electrochemical electrodes based on Laser Induced Graphene on PECVD a-SiC:H and Polyimide. In: 2022 36th Symposium on Microelectronics Technology (SBMICRO). IEEE, pp 1–4 Pedrotti JJ, Angnes L, Gutz IGR (1996) Miniaturized Reference Electrodes with Microporous Polymer Junctions. Electroanalysis 8:673–675. https://doi.org/10.1002/elan.1140080713 Gustavo Cançado L, Gomes da Silva M, Martins Ferreira EH, Hof F, Kampioti K, Huang K, Pénicaud A, Alberto Achete C, Capaz RB, Jorio A (2017) Disentangling contributions of point and line defects in the Raman spectra of graphene-related materials. 2d Mater 4:025039. https://doi.org/10.1088/2053-1583/aa5e77 Wang H, Wang Y, Cao X, Feng M, Lan G (2009) Vibrational properties of graphene and graphene layers. Journal of Raman Spectroscopy 40:1791–1796. https://doi.org/10.1002/jrs.2321 Kumar V, Kumar A, Lee D-J, Park S-S (2021) Estimation of Number of Graphene Layers Using Different Methods: A Focused Review. Materials 14:4590. https://doi.org/10.3390/ma14164590 Kaur S, Mager D, Korvink JG, Islam M (2021) Unraveling the dependency on multiple passes in laser-induced graphene electrodes for supercapacitor and H2O2 sensing. Mater Sci Energy Technol 4:407–412. https://doi.org/10.1016/j.mset.2021.09.004 Aoki K, Tokuda K (1987) Linear sweep voltammetry at microband electrodes. J Electroanal Chem Interfacial Electrochem 237:163–170. https://doi.org/10.1016/0022-0728(87)85229-4 Szabo A, Cope DK, Tallman DE, Kovach PM, Wightman RM (1987) Chronoamperometric current at hemicylinder and band microelectrodes: Theory and experiment. J Electroanal Chem Interfacial Electrochem 217:417–423. https://doi.org/10.1016/0022-0728(87)80233-4 Additional Declarations No competing interests reported. Supplementary Files 2023Bandmicroelectrodes8SI.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 06 Apr, 2024 Reviews received at journal 11 Mar, 2024 Reviewers agreed at journal 11 Mar, 2024 Reviews received at journal 29 Feb, 2024 Reviewers agreed at journal 29 Feb, 2024 Reviewers invited by journal 05 Feb, 2024 Editor assigned by journal 26 Dec, 2023 Submission checks completed at journal 21 Dec, 2023 First submitted to journal 21 Dec, 2023 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-3788473","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":263263963,"identity":"8b393e5b-1f76-4735-818f-e43ee76a5691","order_by":0,"name":"Leonardo M. A. Ribeiro","email":"","orcid":"","institution":"Universidade de São Paulo","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Leonardo","middleName":"M. A.","lastName":"Ribeiro","suffix":""},{"id":263263964,"identity":"f34a05d8-6fc3-4182-b073-a4aa8ce32c6b","order_by":1,"name":"Deissy J. Feria","email":"","orcid":"","institution":"Universidade de São Paulo","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Deissy","middleName":"J.","lastName":"Feria","suffix":""},{"id":263263965,"identity":"4be109a6-8653-4596-a1fc-61404d5277a9","order_by":2,"name":"Paula C. Falcoswki","email":"","orcid":"","institution":"Universidade de São Paulo","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Paula","middleName":"C.","lastName":"Falcoswki","suffix":""},{"id":263263966,"identity":"2c28905c-aea6-4f48-9175-3f7e616c6000","order_by":3,"name":"Marcelo N. P. Carreño","email":"","orcid":"","institution":"Universidade de São Paulo","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Marcelo","middleName":"N. P.","lastName":"Carreño","suffix":""},{"id":263263967,"identity":"1410c85c-ba07-454b-aa48-85375b94089a","order_by":4,"name":"Inés Pereyra","email":"","orcid":"","institution":"Universidade de São Paulo","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Inés","middleName":"","lastName":"Pereyra","suffix":""},{"id":263263968,"identity":"d63aa0c1-7cdb-4dbe-ba3e-972b6482b962","order_by":5,"name":"Mauro Bertotti","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAxklEQVRIiWNgGAWjYDACCSjNzwxlGBCl5QCDgYRkM8laDA4Qq0V3dvOxzx8q/tQZH2fewMzz5w6DufQB/FrM7hxLnnHgjIGE2WG2AmbetmcMln0JBLTcyDFmONgG0sJjwMzbcJjB4AwBh5ndyP8M1mLcDNTC84coLTnMYC1A9UDERoyWO8eMGc6cMZacAfTLwbltz3gsewhpud38mKGiQo6fv//wxgdv/tyRM+choAUZgKLmACkaIJF4gCQdo2AUjIJRMDIAAMEVQUhVhDVgAAAAAElFTkSuQmCC","orcid":"","institution":"Universidade de São Paulo","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Mauro","middleName":"","lastName":"Bertotti","suffix":""}],"badges":[],"createdAt":"2023-12-21 19:14:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3788473/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3788473/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":48919767,"identity":"dcda517b-cfff-495c-98c7-273b00f75e66","added_by":"auto","created_at":"2023-12-28 14:38:50","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":135866,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of the production and measurements of laser-induced graphene band microelectrodes.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3788473/v1/a499b1c9ad94e99a620cd9e1.png"},{"id":48918945,"identity":"1d8ce80e-2016-40a6-a956-f313d8180579","added_by":"auto","created_at":"2023-12-28 14:30:50","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":815883,"visible":true,"origin":"","legend":"\u003cp\u003eOptical image of the graphene trails (a); Raman map of the marked region (b); Raman spectra at \u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u003cbr\u003e\n marked spots A, B, and C (c); corresponding normalized spectra (d).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3788473/v1/0be87b81b1f28d8396c954bb.png"},{"id":48918946,"identity":"0906a3af-b8e3-49b3-aee0-f582a41c176f","added_by":"auto","created_at":"2023-12-28 14:30:50","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":428533,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of the obtained graphene trails: (a) maximum and (b) minimum separation; (c) and (d) different magnifications of the cross-sectional area.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3788473/v1/62e880f879a555c6fb9ae097.png"},{"id":48918938,"identity":"fa48e370-a5d4-4ebc-973f-4cfa52a8410f","added_by":"auto","created_at":"2023-12-28 14:30:50","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":12158,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eCV recorded in 5 mM ferricyanide + 1.0 M KCl solution using one individual microband. Scan rate: 10 mV/s.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3788473/v1/eb015b12aba2cec651f5e60b.png"},{"id":48918940,"identity":"65dc8566-91b1-4679-8ce5-fd3bc6dfce60","added_by":"auto","created_at":"2023-12-28 14:30:50","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":13179,"visible":true,"origin":"","legend":"\u003cp\u003eGenerator/collector experiment performed in a 5 mM ferricyanide + 1.0 M KCl solution. The black line corresponds to WE1, and the red line corresponds to WE2 (polarized at 0.6 V). Scan rate: 10 mV/s.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3788473/v1/54e4cfc7cd82e50ad521c646.png"},{"id":48918942,"identity":"47839732-ec27-4386-ace4-78e9ffb50011","added_by":"auto","created_at":"2023-12-28 14:30:50","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":12598,"visible":true,"origin":"","legend":"\u003cp\u003eApproach curves recorded with a Pt microelectrode (E = 0.1 V) in a 5 mM ferricyanide + 1.0 M KCl solution. Substrates: microband electrode (red line) and an insulating substrate (Kapton, black line).\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3788473/v1/80bf75ae24869ab47c2435e8.png"},{"id":48918943,"identity":"1aee1fe4-8eb7-4d83-8277-a91a877c3418","added_by":"auto","created_at":"2023-12-28 14:30:50","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":180579,"visible":true,"origin":"","legend":"\u003cp\u003eSECM image of graphene microband electrodes (WE1 and WE2) recorded in a 5 mM ferricyanide + 1.0 M KCl solution using a Pt microelectrode (E = 0.1 V). The tip-substrate distance was set at 15 µm\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-3788473/v1/0370dd8119507540fbc10a71.png"},{"id":48919766,"identity":"eaea3335-427c-48cd-94fa-e06d814b1881","added_by":"auto","created_at":"2023-12-28 14:38:50","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":65482,"visible":true,"origin":"","legend":"\u003cp\u003eVoltammograms recorded with the proposed graphene microband electrode in a) 0.5 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e in the absence (black curve) and presence (red curve) of 1 mM caffeic acid and b) PBS in the absence (black curve) and presence (blue curve) of 1 mM paracetamol. Scan rate = 50 mV/s.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-3788473/v1/5f53f3365b76ea60fd5dd6be.png"},{"id":48921226,"identity":"ff241669-d33b-438b-81d0-a6b7b4c68279","added_by":"auto","created_at":"2023-12-28 14:46:52","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1788942,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3788473/v1/5afd4b6e-40e5-4160-a5a8-c081725a9131.pdf"},{"id":48918939,"identity":"634693e9-779a-4762-8622-a2e36f77d526","added_by":"auto","created_at":"2023-12-28 14:30:50","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":188831,"visible":true,"origin":"","legend":"","description":"","filename":"2023Bandmicroelectrodes8SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-3788473/v1/1de6f45c1121d144aa37eb40.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Low-Cost Laser for Affordable Graphene-Induced Microband Sensor Fabrication","fulltext":[{"header":"Introduction","content":"\u003cp\u003eGraphene-based electrochemical sensors are promising for detecting and measuring various chemical and biological substances [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The large surface area, exceptional electrical conductivity, and unique mechanical and chemical properties of graphene make it an excellent material for electrochemical sensors [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Such materials can be used to fabricate electrochemical electrodes with small dimensions, usually referred to as microelectrodes, which present several advantages compared to their counterparts of conventional sizes. These include enhanced mass transport because of radial diffusion at the surface edges, enabling increased current density and greater sensitivity to voltammetric and amperometric measurements. The small dimensions also contribute to minimizing the iR drop due to the decrease in the double-layer capacitance. Hence, measurements can be performed without supporting electrolytes or in highly resistive media. When fabricated in the overall nanometric or micrometric dimension, these devices can be used for measurements in biological systems with high spatial resolution without significant tissue damage.\u003c/p\u003e \u003cp\u003eMicroelectrodes with different geometries, including disc, cylindrical, and band designs, have been constructed [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. This last geometry is interesting because one of the dimensions is on the micro or nanoscale range, but the other can be extended to the centimeter range. Microband electrodes and their arrays have been used in various fields, such as food processing and medical and environmental analysis [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. As a microelectrode, the microband electrode also has increased sensitivity owing to the high mass transport rate originating from radial diffusion [\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eBand microelectrodes have been fabricated using different methods, mainly photolithography, screen printing, vacuum evaporation, and sputter deposition methods [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Because of the advantages mentioned above, these materials have attracted attention for electroanalytical applications, and several examples can be found in the literature [\u003cspan additionalcitationids=\"CR13 CR14\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The use of such devices in flowing systems has also been explored[\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], as well as to obtain analytical [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] and kinetic [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] information in redox systems. The separation between two adjacent band microelectrodes and the influence of these two microelectrodes on the interaction of diffusion fields have been examined in several works [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDirect laser writing or laser-induced graphene (LIG) is a method [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] that allows the production of graphene, mostly 3D (foam-like), trails that can work as microband electrodes. The LIG process involves the use of different types of lasers (CO\u003csub\u003e2\u003c/sub\u003e, UV, and visible) with different wavelengths and powers to irradiate the surface of a substrate that contains carbon atoms, such as polydimethylsiloxane (PDMS) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], polyimide (PI) [\u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], polyetherimide (PEI), polyethersulfone (PES), and a variety of other materials [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Through a photothermal process [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], the surface material absorbs laser light, causing local heating to temperatures from 800\u0026deg;C to more than 2500\u0026deg;C, depending on the laser type and power. This results in a sublimation process where bonds such as C-H, C-N, C\u0026thinsp;=\u0026thinsp;O, and C-O are broken, leading to the elimination of N, O, and other atoms as gaseous compounds, and the remaining carbon atoms are rearranged on the surface to form a graphene structure [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. The overall method is relatively simple, with the irradiated sample kept under atmospheric conditions, with no need for vacuum, precursor gases, or external heat sources other than the laser itself.\u003c/p\u003e \u003cp\u003eIn this work, graphene microbands were fabricated by direct laser writing utilizing a low-cost, low-power blue laser (500 mW, 405 nm). The microband electrodes were patterned at room temperature on polyimide tape fixed to a glass slide. The graphene quality was studied mainly by Raman spectroscopy, electron microscopy, and electrical conductivity measurements. The devices were fully characterized by surface and electrochemical techniques, and encouraging results were achieved regarding analytical applications. The proposed method offers a simple and fast alternative approach that can be easily employed for mass-production electrochemical devices, and preliminary results on caffeic acid and paracetamol detection are shown.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eDevice Construction\u003c/h2\u003e \u003cp\u003eThe electrodes were fabricated utilizing Kapton\u0026reg; polyimide tape as a carbon precursor, approximately 100 \u0026micro;m thick, with silicone adhesive. This polymer was chosen due to its thermal stability up to 400\u0026deg;C and low thermal conductivity and because it leads to graphene films with very high electrical conductivity. The tape was fixed on a 2.5 cm \u0026times; 2.5 cm glass slide previously cleaned with acetone and ethanol, not leaving air pockets when the tape adhered to the support. The conductive graphene pattern was obtained using a commercial laser diode driven by a computer-controlled XYZ positioning table. The electrode geometry templates were produced on AutoCAD\u0026reg; 2016 software and exported to the driving software that controls the XY scan velocity and direction. The laser beam has a wavelength centered at 405 nm, 500 mW power, and a focal spot size of approximately 180 \u0026micro;m. To obtain the optimal conditions, as determined in previous work [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], the glass/Kapton substrates were placed on a horizontal holder at a constant distance of 12.7 cm from the head of the laser. The scan was performed at a 250 mm/min writing speed in an ambient atmosphere.\u003c/p\u003e \u003cp\u003eEight linear devices were produced per slide, as shown in Fig.\u0026nbsp;1a. Afterwards, each device was isolated by cutting the slide into 1.3 \u0026times; 0.6 cm\u003csup\u003e2\u003c/sup\u003e pieces (Fig.\u0026nbsp;1b). The device consists of two graphene bands of 10 mm in length and 150 \u0026micro;m in width. The separation between bands varied from 40 \u0026micro;m to 850 \u0026micro;m, and a device with 200 \u0026micro;m separation between adjacent microbands was employed in this work. Electrical contacts were established between a copper wire and graphene microbands utilizing conductive ink (Bare Conductive\u0026reg;), which consists of a combination of carbon black and graphite in a water-soluble solvent (Fig.\u0026nbsp;1c). To control the active area and protect the device, transparent epoxy resin (Araldite\u0026reg;) was deposited on the electrical contacts (Fig.\u0026nbsp;1d). After device construction, an electrochemical test was performed using ferricyanide as a redox probe in KCl medium, as described below (Fig.\u0026nbsp;1e). Finally, the electrical resistance of the microbands was measured through the two ends (Fig.\u0026nbsp;1c and 1f).\u003c/p\u003e \u003cp\u003e \u003cb\u003eFigure\u0026nbsp;1\u003c/b\u003e \u003cem\u003eSchematic illustration of the production and measurements of laser-induced graphene band microelectrodes.\u003c/em\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eLIG characterization\u003c/h2\u003e \u003cp\u003eThe structural and morphological characterization of the produced graphene trails was performed by optical microscopy, scanning electron microscopy (FESEM JEOL JSM-7401F), and confocal Raman spectroscopy (WITEC, Alpha300 R) using a green laser line (532 nm) and 30 mW of power. Spectra were acquired using 10x and 50x objective lenses. Raman mapping of the 2D band was performed in a rectangular area of 400 \u0026micro;m \u0026times; 100 \u0026micro;m along the trail to evaluate the continuity and uniformity of the produced 3D graphene. Additionally, Raman spectra were taken at several points within that area. Each spectrum was an average of 10 acquisitions with 2 s of accumulation time per acquisition. The electrical conductivity of the graphene trails was measured before and after the electrochemical experiments to evaluate the eventual contamination or damage of the graphene trails with the tested chemical solution. For this purpose, the ends of the trails (Fig.\u0026nbsp;1f) were connected to a copper wire with conductive ink and then covered with a final insulating layer of epoxy. The I versus V curves were obtained by connecting the wires to a source measurement unit (Keysight SMU model B2902A). The electrical resistance was measured, and the sheet resistance of the produced graphene was estimated.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eElectrochemical Measurements\u003c/h2\u003e \u003cp\u003eAll the electrochemical measurements were performed with a PGSTAT 128 potentiostat from Eco Chemie (Utrecht, Netherlands) using Nova control software for data acquisition. A 3-electrode system was used for most of the electrochemical measurements, with a Ag|AgCl \u003csub\u003e(KCl sat)\u003c/sub\u003e homemade reference electrode [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] and a platinum wire as the counter electrode. Scanning electrochemical microscopy (SECM) was performed with an SECM workstation from Sensolytics (Bochum, Germany). The Pt microelectrode (25 \u0026micro;m in diameter from Goodfellow (Huntington, England)) used in the SECM experiments was fabricated with a borosilicate glass micropipette pulled using P-97 equipment from Sutter Instrument (Novato, USA). The RG (RG\u0026thinsp;=\u0026thinsp;rg/r, where rg is the radius of the electrode along with the surrounding insulator and r is the radius of the Pt disc fiber) of the microelectrode was determined by fitting the approach curve to the theoretical curve (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e) using ferricyanide as a reversible electrochemical probe. The experiment was performed using polyimide tape as an insulating substrate, and the RG value was found to be approximately 12.\u003c/p\u003e \u003cp\u003eAll the solid chemicals used were of analytical grade and used without further purification. The solutions were prepared using deionized water processed on a purifying system from Nanopure Infinity (Barnstead, US). K\u003csub\u003e3\u003c/sub\u003e[Fe(CN)\u003csub\u003e6\u003c/sub\u003e] and KCl were obtained from Sigma Aldrich (San Luis, USA). Cyclic voltammetry (CV) and SECM experiments were carried out in a 5 mM K\u003csub\u003e3\u003c/sub\u003e[Fe(CN)\u003csub\u003e6\u003c/sub\u003e]\u0026thinsp;+\u0026thinsp;1.0 M KCl solution. The CVs were recorded in a potential range comprising 0.6 to -0.2 V, and the SECM experiments were performed with the platinum microelectrode (tip) polarized at 0.1 V. The SECM images were obtained by scanning the tip in the x-y plane at a tip-substrate distance of 15 \u0026micro;m above the microbands.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003eStructural, Electrical, and Morphological Characterization\u003c/h2\u003e\n \u003cp\u003e\u003cstrong\u003eThe\u003c/strong\u003e Raman spectra in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea show an optical image of the analyzed trail region, and the corresponding 2D band map is depicted in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb. Different intensity regions are observed in the mapping, and to understand the origin of these variations, Raman spectra were recorded at the spots marked A (more intense), B (medium intensity) and C (less intense) (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec and d).\u003c/p\u003e\n \u003cp\u003eAll the spectra present the typical D, G, and 2D bands for graphene. The D peak at ~\u0026thinsp;1350 cm\u003csup\u003e-1\u003c/sup\u003e is induced by defects and bent sp\u003csup\u003e2\u003c/sup\u003e carbon bonds, the G peak at ~\u0026thinsp;1580 cm\u003csup\u003e-1\u003c/sup\u003e (1st order allowed) is due to the stretching mode of sp\u003csup\u003e2\u003c/sup\u003e C-C bonds, and the 2D peak at ~\u0026thinsp;2700 cm\u003csup\u003e-1\u003c/sup\u003e (2nd order zone-boundary phonons) provides information on the approximate number of layers (or multilayer formation) based on its position, shape, intensity, and full width at half-maximum (FWHM). In Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec, the spectra for spots A, B, and C are observed, and the difference in intensity can be appreciated. Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed shows the spectra normalized to the G band, allowing us to evaluate the relative intensities of the D, G, and 2D bands. As observed, the three spectra are very similar, indicating that all the mapped area is covered by graphene, varying from three to seven layers, as estimated from the I\u003csub\u003e2D\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e ratio. These results suggest that the observed variations in intensity are due to the nonplanar nature of the mapped trail surface, as shown in the SEM images in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, rather than to the nonuniform quality of the produced graphene.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e shows the top view of trails with the (a) maximum (~\u0026thinsp;850 \u0026micro;m) and (b) minimum (~\u0026thinsp;40 \u0026micro;m) band separations. Trails exhibiting a periodic sequence of bumps with different widths and heights can be observed, which is attributed to the nonuniform movement of the laser due to the utilized step motor. The cross-sections of the trails at different magnifications are shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed, where the 3D and foam-like features of the obtained graphene are evident. In this way, as the Raman mapping is recorded while maintaining a constant focus, the focus is lost as different height points are analyzed, leading to the observed intensity changes. The average mapping spectrum was used to estimate the crystallite size (L\u003csub\u003ea\u003c/sub\u003e)[\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e], the distance between point defects (L\u003csub\u003ed\u003c/sub\u003e), and the number of layers[\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e], leading to values of 8.9 nm for L\u003csub\u003ea\u003c/sub\u003e, 7.0 nm for L\u003csub\u003ed\u003c/sub\u003e and 3 to 7 for the number of graphene layers. The number of graphene defects on the polyimide can be attributed to the small graphene sheets that exhibit a structure similar to that of foam, as shown in the SEM images (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed).\u003c/p\u003e\n \u003cp\u003eThe electrical conductivity measurements, performed on 10 electrodes before the electrochemical characterization, led to an average sheet resistance (R\u003csub\u003es\u003c/sub\u003e) of 32\u0026thinsp;\u0026plusmn;\u0026thinsp;4 Ω/sq. In comparison, the R\u003csub\u003es\u003c/sub\u003e value for 8 electrodes after electrochemical measurements was 32\u0026thinsp;\u0026plusmn;\u0026thinsp;2 Ω/sq, following the best results reported in the literature for LIG graphene [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]; this is an indication that the electrochemical procedure induced no changes.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003eElectrochemical characterization\u003c/h2\u003e\n \u003cp\u003ePreliminary experiments with the fabricated device involved recording a CV with one of the microbands in a solution containing ferricyanide, a chemical species with well-known reversible electrochemical behavior. At a relatively low scan rate (10 mV/s), a sigmoidal curve was obtained, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. At such an experimental long-term window (low scan rate), an almost steady-state type voltammetric profile is observed because the area of the diffusion layer becomes comparable to the smallest dimension of the microband after several seconds of electrolysis. However, it should be noted that for band microelectrodes, which possess a macroscopic dimension in the order of mm in length and the other (width) in the \u0026micro;m range, a true steady state is never reached [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eOn the other hand, at faster scan rates, the voltammetric profile becomes more peak-shaped because the size of the diffusion layer becomes less or comparable to the size of the microscopic domain. Consequently, a peak-shaped response is evident and is likely to follow the Randles\u0026ndash;Sevcik equation. Fig. S2 shows CVs recorded with one microband at various scan rates, and typical peak-shaped curves can be observed. Again, at a relatively low scan rate, an almost sigmoidal-shaped CV characteristic of radial diffusion was obtained (red curve).\u003c/p\u003e\n \u003cp\u003eAn additional voltammetric experiment was performed to assess the response of each microband electrode and to investigate whether both microband electrodes could be interconnected. Fig. S3 shows the results, and it can be concluded that the voltammetric responses of both microbands are very similar, which is the first confirmation that the fabrication process yields electrodes with reproducible electrochemical profiles. The microband electrodes were then interconnected, and a new CV was recorded, generating the voltammetric red curve. The peak current obtained with the interconnected microbands was double that obtained with the individual microbands, confirming that the proposed method generates similar microbands.\u003c/p\u003e\n \u003cp\u003eThe reproducibility of a set of fabricated microband electrodes was explored by comparing cyclic voltammetric responses obtained using ferricyanide as a probe. Analysis of the voltammetric data revealed that the relative standard deviation was 13% (n\u0026thinsp;=\u0026thinsp;10), and a repeatability value of 2.2% was found (n\u0026thinsp;=\u0026thinsp;10) (Fig. S4).\u003c/p\u003e\n \u003cp\u003eThe repeatability test (Fig. S4B) yielded a relatively low value (2.2%), indicating that the same device exhibits high stability and consistency during repeated measurements. This result suggested that once a specific graphene microband electrode is fabricated, its electrochemical performance is reliably maintained over multiple measurements. This finding is encouraging because it demonstrates the potential for consistent and repeatable results within a single device, which is crucial for practical applications. The difference among devices must be related to minor geometrical variations inherent to the fabrication process. The stability of the devices is very good, and an automated process should improve the reproducibility. In summary, while the reproducibility of the devices may benefit from further optimization, the repeatability results indicate that individual devices exhibit excellent stability.\u003c/p\u003e\n \u003cp\u003eThe diffusional interaction between dual microelectrodes can be studied by changing the potential of one electrode (generator electrode) and detecting the products at the other electrode (collector electrode), whose potential is set to regenerate the starting material. A similar experiment was carried out with a fabricated device in which the distance between the two microbands was 200 \u0026micro;m. In this experiment, the potential of W1 was changed from an initial value to a final value, while the potential of the second electrode (WE2) was kept constant at 0.6 V, a potential value where the anodic oxidation of the species electrogenerated at the first electrode (WE1) is mass-transport controlled. The following equations (1 and 2) describe both processes:\u003c/p\u003e\n \u003cp\u003e\u003cimg 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\" width=\"931\" height=\"134\"\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e shows the CVs recorded at both WE1 and WE2. The measured collection efficiency (the ratio between the limiting current values at the collector and generator electrodes) was calculated as 24.2%, which is a relatively low value but determined by the considerable distance between both microelectrodes. This experimental outcome unequivocally validates the ability of the two microbands to act as separate and self-reliant electrodes (if required to operate independently), thereby substantiating their suitability for simultaneous and discriminating electrochemical sensing applications.\u003c/p\u003e\n \u003cp\u003eThe final characterization of the microband electrodes was performed by scanning electrochemical microscopy (SECM), a technique that offers valuable localized information on surface electrochemical reactivity with high resolution. A first investigation was conducted to assess the reactivity of the microband through approach curves. Ferricyanide was used as an electrochemical probe, and a Pt microelectrode, used as a tip, was used to carefully approach the microband surface (substrate). In this experiment, the potential of the tip is set at a value corresponding to the steady-state limiting current, i.e., the reduction of ferricyanide to ferrocyanide is mass-transport controlled. Ferrocyanide can reach the substrate and be electrochemically reduced, depending on the nature of the substrate. If the substrate is conductive, ferricyanide can be regenerated, and it diffuses back to the tip, causing the so-called SECM positive feedback. The extent of such an effect becomes more critical as the tip-to-substrate distance decreases. Figure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e shows the approach curve obtained in this experiment (red curve), and the positive feedback confirms that the surface is electrochemically reactive. A parallel study was performed with an insulating substrate (Kapton), and as expected, the current decreased as the tip approached the substrate because of the hindered diffusion effect (negative feedback); i.e., ferricyanide was not regenerated at the substrate.\u003c/p\u003e\n \u003cp\u003eThrough SECM imaging, the conductivity of a surface can be assessed at high resolution, providing deeper insights into the electrochemical performance and quality of the fabricated microband electrodes. Figure \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e shows an SECM image of the device containing two microbands (WE1 and WE2) in a ferricyanide solution. Higher currents correspond to increased reactivity because of positive feedback. By inspecting the images, one can conclude that the reactivity is not homogeneous through the extension of a single microband, and some spots of higher reactivity are present in both microbands (blue and green). The other sections of the bands are seen in the yellow zones, which correspond to more reactive surfaces than insulating Kapton (orange regions). These results are consistent with the Raman mapping and SEM experiments (see Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e) and suggest that the observed variations in reactivity or current are related to the 3D (foam-like) character of the graphene in the microbands.\u003c/p\u003e\n \u003cp\u003eTherefore, integrating SECM with generator/collector experiments confirms the independence of microbands as separate electrodes and allows for a comprehensive characterization of their surface properties and conductivity distribution, revealing that the reactivity is not homogeneous within the microband. While such inhomogeneity of the active material on the microband restrains its use for kinetic studies, where the exact geometry of the electrodes and their homogeneity are critical factors for obtaining reliable results, the proposed method can still be used for other applications that do not depend on an electrode with rigorous homogeneous geometry.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003eMathematical Method for Current Calculations\u003c/h2\u003e\n \u003cp\u003eThe experimental current (I\u003csub\u003eexp\u003c/sub\u003e) was compared with the theoretical current (I\u003csub\u003etheo\u003c/sub\u003e) for a microband electrode using Eq.\u0026nbsp;(3) proposed by Szabo and coworkers [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e]. This equation enables the calculation of the theoretical current for a microband electrode over the entire time range.\u003c/p\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\frac{{I(t)}}{{nFCDl}}=\\frac{{\\pi {e^{ - 2\\sqrt {\\pi \\tau /5} }}}}{{4\\sqrt {\\pi \\tau } }}+\\frac{\\pi }{{\\ln [{{(64{e^{ - \\Upsilon }}\\tau )}^{1/2}}+{e^{5/3}}]}}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e Eq. 3\u003c/p\u003e\n \u003cp\u003eWhere \u003cem\u003en\u003c/em\u003e is the number of electrons transferred, \u003cem\u003eF\u003c/em\u003e is the Faraday constant, \u003cem\u003ec\u003c/em\u003e is the bulk concentration of the reactant, \u003cem\u003eD\u003c/em\u003e is the diffusion coefficient of the reactant, \u003cem\u003el\u003c/em\u003e is the length of the electrode, \u003cem\u003ew\u003c/em\u003e is the width of the band electrode, \u003cem\u003et\u003c/em\u003e is the time, \u003cem\u003e\u0026upsih;\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.5772156, and \u003cem\u003e\u0026tau;\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eDt/w\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e.\u003c/p\u003e\n \u003cp\u003eSEM and optical microscopy images were obtained to confirm the length and width of the band electrode. The chronoamperograms obtained for 4 different microbands in the last section of the experiment (from 25 to 60 s) are presented in Fig. S5. Measurements were carried out at E\u0026thinsp;=\u0026thinsp;0.1 V, an experimental condition in which the cathodic reduction of the electroactive species (ferricyanide) is diffusion controlled. The current was measured at \u003cem\u003et\u003c/em\u003e\u0026thinsp;=\u0026thinsp;60 s, and the results are summarized in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n \u003cdiv align=\"char\" class=\"colspec\"\u003e\u003cbr\u003e\u003c/div\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eExperimental and theoretical current values measured at 60 s for 4 microband electrodes.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eDevice\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003el (cm)\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ew (cm)\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eexp\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e(\u0026micro;A)\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003etheo\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e(\u0026micro;A)\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eDeviation (%)\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0155\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0154\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0157\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0154\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e17.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003eThe deviation between the predicted and experimental results in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e ranged from 7.5\u0026ndash;20.6%, and the average value was calculated as 13%, which is surprisingly good considering that the utilized theoretical model is valid for coplanar electrodes and that the actual electrodes have a 3D structure, as demonstrated by the Raman and SEM results.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003ePractical application\u003c/h2\u003e\n \u003cp\u003eCaffeic acid is an acid-derived phenolic compound usually found in green tea, coffee, fruits, and vegetables. Paracetamol, also known as acetaminophen, is another compound commonly used as an analgesic and antipyretic. Electrochemical sensors offer several benefits concerning quantification, such as high sensitivity and low cost. In this way, preliminary experiments were performed to evaluate the response of the proposed graphene microband electrodes for caffeic acid and paracetamol detection. Figures \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003eb show voltammograms recorded with the proposed microband in solutions containing caffeic acid (1 mM) and paracetamol (1 mM), respectively. These results confirm the reliability of the proposed device as a helpful platform for the inexpensive and straightforward detection of analytes at low concentrations.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe results presented in this study demonstrate that the graphene microband electrode device exhibits promising characteristics, making it a cost-effective and reproducible option for various applications. These considerations are based on two facts: the graphene quality and the low cost of the material production process. As shown, the produced material has a high electrical conductance (30 Ω/square) in a few layers (3 to 7) of graphene. The production process utilizes a low-cost (a few tens of dollars) and low-power blue diode laser. To our knowledge, this is the first study in which laser-induced graphene exhibiting the abovementioned properties was produced with this laser type. Considering its affordability and reproducibility, there is great potential for the widespread utilization and exploration of these devices in fields such as electrochemical sensing, energy storage, and beyond. Continued research and development efforts will uncover new opportunities and applications for this versatile graphene microband electrode device.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eL. M. A. R: Conceptualization, Methodology, Formal analysis, Writing - original draft, review and editing; and prepared figures 1, 4, 5, 8 and S2-S6D. J. F.: Conceptualization, Methodology, Formal analysis, review and editing; and prepare figure 2 and 3P. C. F.: Methodology, Formal analysis, review, and editing; and prepare figure 6, 7 and S1.M. N. P. C.: Supervision, Writing - review;I. P.: Conceptualization, Supervision, Writing - review;M. B.: Conceptualization, Methodology, Supervision, Writing - review and editing.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThe authors would like to thank the National Council for Scientific and Technological Development (CNPq 140259/2021-0) and the S\u0026atilde;o Paulo State Research Foundation (FAPESP 2018/08782-1 and 2022/03665-2) for their financial support.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eNag A, Mitra A, Mukhopadhyay SC (2018) Graphene and its sensor-based applications: A review. Sensors and Actuators A: Physical 270:177\u0026ndash;194. https://doi.org/10.1016/j.sna.2017.12.028\u003c/li\u003e\n\u003cli\u003eCoroş M, Pruneanu S, Stefan-van Staden R-I (2020) Review\u0026mdash;Recent Progress in the Graphene-Based Electrochemical Sensors and Biosensors. J Electrochem Soc 167:037528. https://doi.org/10.1149/2.0282003JES\u003c/li\u003e\n\u003cli\u003eGeim AK, Novoselov KS (2007) The rise of graphene PROGRESS. 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Materials 14:4590. https://doi.org/10.3390/ma14164590\u003c/li\u003e\n\u003cli\u003eKaur S, Mager D, Korvink JG, Islam M (2021) Unraveling the dependency on multiple passes in laser-induced graphene electrodes for supercapacitor and H2O2 sensing. Mater Sci Energy Technol 4:407\u0026ndash;412. https://doi.org/10.1016/j.mset.2021.09.004\u003c/li\u003e\n\u003cli\u003eAoki K, Tokuda K (1987) Linear sweep voltammetry at microband electrodes. J Electroanal Chem Interfacial Electrochem 237:163\u0026ndash;170. https://doi.org/10.1016/0022-0728(87)85229-4\u003c/li\u003e\n\u003cli\u003eSzabo A, Cope DK, Tallman DE, Kovach PM, Wightman RM (1987) Chronoamperometric current at hemicylinder and band microelectrodes: Theory and experiment. J Electroanal Chem Interfacial Electrochem 217:417\u0026ndash;423. https://doi.org/10.1016/0022-0728(87)80233-4\u003c/li\u003e\n\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":"journal-of-applied-electrochemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jach","sideBox":"Learn more about [Journal of Applied Electrochemistry](http://link.springer.com/journal/10800)","snPcode":"10800","submissionUrl":"https://submission.nature.com/new-submission/10800/3","title":"Journal of Applied Electrochemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Band microelectrodes, graphene, electrochemical sensors","lastPublishedDoi":"10.21203/rs.3.rs-3788473/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3788473/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eGraphene microband electrodes were fabricated by direct laser writing on Kapton\u0026reg; polyimide tape utilizing a low-cost, blue laser (500 mW and 405 nm). The structural properties of the graphene were examined by Raman spectroscopy, and key features such as D, G, and 2D bands, and the presence of multilayer structures were revealed. Scanning electron microscopy (SEM) provided insights into the microband morphology, highlighting the 3D (foam-like) nature of the graphene microbands. Electrochemical experiments revealed cyclic voltammetry profiles that demonstrated radial diffusion dominance at low scan rates and Randles\u0026ndash;Sevcik behavior at higher scan rates. Reproducibility and repeatability analyses confirmed the stability and consistency of these microband electrodes within individual devices. Scanning electrochemical microscopy (SECM) images revealed the electrochemical reactivity of the microbands. At a relatively low microband separation (200 \u0026micro;m), the produced material can be collected at the adjacent microband, which was confirmed via generator/collector experiments. Theoretical-experimental comparisons regarding the current measured for a single microband were performed, and the obtained results were in good agreement, with deviations attributed to the 3D morphology of the microbands. This research underscores the potential of these cost-effective and reproducible graphene microband electrodes for diverse applications in electrochemical sensing, and we present preliminary results on caffeic acid and paracetamol detection.\u003c/p\u003e","manuscriptTitle":"Low-Cost Laser for Affordable Graphene-Induced Microband Sensor Fabrication","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-12-28 14:30:45","doi":"10.21203/rs.3.rs-3788473/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-04-06T20:26:16+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-03-11T10:53:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"6d79f900-7d65-4d30-8614-a2dc71d778b0","date":"2024-03-11T05:13:38+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-02-29T07:14:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"2970f1d8-faa2-46e3-ac97-4f6d07c4edb0","date":"2024-02-29T06:16:25+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-02-06T04:30:38+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-12-26T05:21:13+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2023-12-22T04:22:41+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Applied Electrochemistry","date":"2023-12-21T19:02:03+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-applied-electrochemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jach","sideBox":"Learn more about [Journal of Applied Electrochemistry](http://link.springer.com/journal/10800)","snPcode":"10800","submissionUrl":"https://submission.nature.com/new-submission/10800/3","title":"Journal of Applied Electrochemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"3eec31d3-3bf2-48f4-9152-b5b103b85a4f","owner":[],"postedDate":"December 28th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-04-20T16:58:42+00:00","versionOfRecord":[],"versionCreatedAt":"2023-12-28 14:30:45","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3788473","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3788473","identity":"rs-3788473","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}