In situ deposition of bismuth on pre-anodized screen-printed electrode for sensitive determination of Cd2+ in water and rice with a portable device

In situ deposition of bismuth on pre-anodized screen-printed electrode for sensitive determination of Cd2+ in water and rice with a portable device | 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 Article In situ deposition of bismuth on pre-anodized screen-printed electrode for sensitive determination of Cd2+ in water and rice with a portable device Yongfang Li, Zijun Wang, Xuan Chen, Zhijian Yi, Rui Wang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4600103/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 08 Aug, 2024 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract Electrochemical detection is favorable for the rapid and sensitive determination of heavy metal cadmium. However, the detection sensitivity needs to be further improved, and a portable, low-cost device is needed for on-site detection. Herein, an in-situ bismuth modified pre-anodized screen-printed carbon electrode (SPCE) was developed for Cd 2+ determination by square wave anodic stripping voltammetry (SWASV). The in-situ bismuth modification enhances the enrichment of Cd 2+ , and together with pre-anodization improve the electron transfer rate of electrode, thus enhancing the detection sensitivity. In addition, a self-made PSoC Stat potentiostat coupled with a stirring device was fabricated for portable electrochemical detection. After comprehensive optimization, the developed method can reach a testing time of 3 min, a detection limit of 3.55 µg/L, a linear range of 5-100 µg/L, and a recovery rate of 91.7%-107.1% in water and rice samples for Cd 2+ determination. Therefore, our method holds great promise for the rapid, sensitive and on-site determination of Cd 2+ in food samples. pre-anodization bismuth modification electrochemical sensor Cd2+ portable device Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Cadmium (Cd) is a toxic heavy metal that has multiple toxic effects on the human kidney, liver, nervous and cardiovascular systems [ 1 ] . With the increase of industrial activities such as smelting operations, electroplating, pigments, fertilizers and mining, a large amount of industrial wastewater containing cadmium was discharged without treatment, seriously polluting drinking water and soil [ 2 ] . The consumption of cadmium-contaminated water and rice poses a great threat to human health [ 3 ] . Therefore, sensitive and rapid determination of cadmium in food is of great significance for environmental protection and food safety. Conventional methods for cadmium detection include atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS) and inductively coupled plasma mass spectrometry (ICP-MS) [ 4 – 6 ] . Although these methods possess high sensitivity, accuracy and stability, they need complex instrument operation, long operation time and high operating cost, which are not suitable for rapid field detection [ 7 ] . Anodic stripping voltammetry is considered as a powerful tool for heavy metal detection [ 8 , 9 ] . In this method, Cd 2+ is enriched to the electrode surface at a constant potential and reduced to Cd 0 . Then Cd 0 is oxidized to Cd 2+ under scanning voltage and stripped out into the electrolyte to generate a current. The current value is proportional to the content of metal ions, and each metal ion has its characteristic oxidation potential [ 10 , 11 ] . Electrode modification is an important means to improve the analytical sensitivity of electrochemical sensors. Bismuth modified electrode has been widely used for Cd determination and the simultaneous determination of Cd, Pb and Zn [ 12 – 14 ] . The modification of bismuth can be finished by in-situ deposition, ex-situ deposition or dropping ways [ 15 , 16 ] . In-situ deposition owns great advantage for that the co-deposition of Bi 3+ and Cd 2+ can enhance the enrichment of Cd 2+ , thus improving the detection sensitivity [ 17 ] . Besides, in-situ deposition is easy handling and time-saving, avoids the risk of degradation and uneven distribution of modified bismuth [ 18 ] . Except for metal material modification, electrochemical activation can also enhance the detection sensitivity of electrode [ 19 ] . Pre-anodization is an effective method for electrode activation by accelerating the electron transfer between substance and electrode [ 20 , 21 ] . It owns the characteristics of less reagent and simple operation [ 22 ] . Moreover, to achieve point-of-need quantitation of heavy metal Cd 2+ , a portable and low-cost device capable of transmitting, collecting and displaying electrochemical signals is urgently required. Herein, by combining pre-anodization technique and in-situ deposition method, an in-situ bismuth modified pre-anodized screen-printed carbon electrode (Bi/Pre-anodized SPCE) for Cd 2+ determination was prepared, and the detection was conducted on a portable, self-made and low-cost potentiostat coupled with a stirring device (Fig. 1 ). The pre-anodization was carried out in PBS (pH = 9) by cyclic voltammetry (CV) method. Then Bi 3+ and Cd 2+ were co-deposited on the pre-anodized electrode and Cd 2+ was stripped out for determination by square wave anodic stripping voltammetry (SWASV). The developed electrochemical sensor demonstrated good performance for Cd 2+ determination with limit of detection as low as 0.15 µg/L and 3.55 µg/L using commercial and self-made potentiostat, respectively. The test could be completed within 3 min with good repeatability and specificity. The recovery rates in water and rice samples ranged from 91.7–107.1%. 2. Materials and methods 2.1 Reagents and materials Sodium acetate, sodium bromide, acetic acid and hydrogen peroxide were purchased from Guangzhou Chemical Reagent Factory. K 3 [Fe (CN 6 )] and K 4 [Fe (CN) 6 ] were purchased from Shanghai Maclin Biochemical Technology Co., LtD. The 0.22 µm filter membrane was purchased from Beekman Biological Corporation. Stock solution of bismuth ion and cadmium ion (1000 µg/mL) were purchased from Beijing General Research Institute of Non-Ferrous Metals. Screen-printed carbon electrode (diameter 2.8mm) was obtained from Wuhan Zhongke Zhikang Biotechnology Co., LtD. All solutions were prepared using ultrapure water produced by Milli-Q ultrapure water (Millipore Company, USA). 2.2 Instruments Scanning electron microscope (SEM) images were acquired on a a field emission scanning electron microscope (Quattro S, Thermo Fisher Scientific, USA). Energy dispersive X-ray (EDX) spectrum was collected on an energy dispersive spectrometer (Ultim Max Oxford Instruments LtD., U.K.). Electrochemical impedance spectroscopy (EIS) was performed with a potentiostat (Autolab 302N, Metrohm Autolab B.V., Switzerland). Other electrochemical measurements were performed on a CHI1440 constant potential instrument (Shanghai Chenhua Instrument Co., LtD.) and a self-made PSoC Stat potentiostat (Fig. S1 ). A stirring device containing an SPCE connector, a sample cell and a time- and speed-regulated stirring motor was self-made for the experiment (Fig. S2). 2.3 Experimental methods 2.3.1 Pre-anodization of screen-printed carbon electrode The screen-printed electrode was pre-anodized by cyclic voltammetry method. The SPCE was scanned for 5 cycles in 0.1 mol/L PBS phosphate buffer solution (pH = 9), with a scanning range of 0.5 ~ 1.7 V and a scanning rate of 0.1 V/s. Then the SPCE was rinsed thoroughly with ultra-pure water and dried at room temperature. 2.3.2 SWASV for Cd 2+ determination 1 mL of 0.1 mol /L acetate buffer (pH 4.5) containing 150 µg/L Bi 3+ , 20 µmol/L NaBr and a certain concentration of Cd 2+ were added into the sample cell. Then the pre-anodized SPCE were immersed into the solution. The detection parameters of SWSV were set as follows: deposition potential is -1.4 V, deposition time is 180 s, potential increment is 4 mV, amplitude is 25 Hz, scanning range is -1.4~ -0.2 V. In the deposition process, the sample cell was rotated by the stirring motor with a stirring rate of 200 rpm. No stirring was provided in the stripping process. All tests were performed at room temperature (26 ± 0.5 ° C). 2.4 Recovery study Tap water and rice samples without Cd were selected for recovery studies. The rice samples were purchased from a local market in Foshan. The tap water was filtered by 0.22 µm microporous filter membrane. Filtered water was adjusted to pH 4.5 by nitric acid, then mixed with an equal volume of 0.2 mol/L acetate buffer solution (pH = 4.5) to obtain the pre-treated tap water sample. The pretreatment of rice samples was referred to the method reported by Wang [ 23 ] . The rice samples were crushed into powder and dried in an oven for 2 hours. 1 g rice powder was dissolved in 10 mL nitric acid and boiled until nearly dry. Then 3 mL H 2 O 2 was added and heated until dry. The residue was dissolved in 25 mL 0.1mol /L acetic acid. After complete vortex oscillation, the solution was filtered by 0.22 µm membrane. The filtrate was adjusted to pH 4.5 by NaOH solution to obtain the pre-treated rice extract. Standard solution of Cd 2+ were added into the pre-treated tap water or rice extract. Then the spiked samples were analyzed by both the established electrochemical method described in 2.3.2 and ICP-MS. 3. Results and discussion 3.1 Study of electrode pre-anodization The effect of solution type on pre-anodization was firstly evaluated. The screen-printed electrode was pre-anodized with 0.1 mol/L HNO 3 , HCl, H 2 SO 4 , NaOH, PBS (pH = 5), PBS (pH = 7) and PBS (pH = 9), respectively. Then the electrochemical characteristics of the electrodes were evaluated by cyclic voltammetry in 5 mmol/L [Fe (CN) 6 ] 3−/4− containing 0.1 mol/L KCl. The scanning range was − 0.5 ~ 0.7 V, the scanning rate was 0.1 V/s. As shown in Fig. 2 a, compared with HNO 3 , HCl, H 2 SO 4 and NaOH, the highest redox current and smallest peak potential difference were obtained when using 0.1 mol/L PBS (pH = 9), indicating an excellent electron transfer ability. Subsequently, PBS solution with different pH values were compared. As shown in Fig. 2 b, PBS (pH = 9) demonstrated the best performance. In addition, compared with bare electrode, pre-anodization definitely improves the electron transfer ability. Next, the effect of scanning turns in pre-anodization was studied. SPCE was pre-anodized in 0.1 mol/L PBS solution (pH = 9) for different scanning cycles, then the SPCEs were characterized by CV in 5 mmol/L [Fe (CN) 6 ] 3−/4− containing 0.1 mol/L KCl. As shown in Fig. 2 c, as the number of scanning cycles varies from 0 to 5, the redox current increases significantly and the peak potential difference decreases markedly. When the number of scanning turns exceeds 5, the peak potential difference is basically unchanged and the redox current decreases slightly (Fig. 2 d). Therefore, scanning turn was set as 5 in the pre-anodization of SPCE. 3.2 Morphological characterization and element analysis of SPCE SEM and EDX were used to characterize the surface of SPCE during modification process. As shown in Fig. S3a-c, pre-anodization and bismuth modification have little effect on the morphology of the electrode surface. Since pre-anodization treatment has a good activation effect on the SPCE, it indicates that the main mechanism of activating the SPCE by pre-anodization is not through cleaning the electrode or other factors that cause great changes in the morphology of the electrode. The in-situ deposited bismuth cannot be observed directly through SEM images, however, EDX spectrum demonstrates the existence of Bi on the surface of SPCE (Fig. S3d). It is attributed to the small size and low content of bismuth. Therefore, the pre-anodized and bismuth modified electrodes will be further characterized by electrochemical methods. 3.3 Electrochemical characterization of SPCE 3.3.1 Electrode performance evaluation with cyclic voltammetry Pre-anodized SPCE was characterized by cyclic voltammetry in 5 mmol/L [Fe (CN)6] 3−/4− and 0.1 mol/L KCl solution at different scanning rates. The scanning range is -0.5 ~ 0.7 V, the scanning rate is 0.05 ~ 0.3 V/s. The redox peak current enhanced with the increasing scanning rate (Fig. 3 a). Ipa and Ipc were linearly correlated with the square root of scan rate (Fig. 3 b), indicating that the redox process is mainly based on diffusion-controlled reactions [ 24 ] . Then different electrodes were evaluated by cyclic voltammetry with scanning rate set as 0.1 V /s. As shown in Fig. 3 c, compared with bare electrode, the redox current increased significantly and the peak potential difference decreased after pre-anodization. On this basis, in situ deposition of metallic bismuth further improves the peak current. In addition, the presence of NaBr in bismuth modification enhanced the peak current. The EIS result was consistent with the CV test for that the Rct decreased with the electrode modification (Fig. 3 d). This suggests that pre-anodization and bismuth modification improve the charge transfer rate of screen-printed electrode [ 25 ] . Furthermore, the effective area of the electrode was calculated by Randles-Sevcik equation [ 24 ] . The equation is shown in (1). I P =2.69×10 5 n 3/2 AD 1/2 v 1/2 C (1) I p is the redox peak current (A), n is the number of transferred electrons (n = 1), A is the active surface area of working electrode (cm 2 ), D is the diffusion coefficient of electroactive substance (cm 2 /s), C is the concentration of electroactive substance (mol/cm 3 ) and v is the scan rate (V/s). For 5 mmol/L of [Fe (CN) 6 ] 3−/4− , n = 1, and D = 6.30×10 − 6 cm 2 /s. After calculation, the effective area of pre-anodized SPCE (0.057 cm 2 ) is about 2.59 times that of the bare electrode (0.022 cm 2 ), and further increased after the in-situ deposition of bismuth, reaching 0.064 cm 2 (without NaBr) and 0.078 cm 2 (with NaBr), respectively. The results demonstrated that the active surface area of the screen-printed electrode is enlarged by pre-anodization and bismuth modification, which is beneficial to improve the sensitivity of the electrochemical sensor. 3.3.2 Electrochemical response of different electrodes towards Cd 2+ Bare SPCE, in situ bismuth modified electrode (Bi-SPCE), Bi/Pre-anodized SPCE without NaBr (Bi/Pre-anodized SPCE (-NaBr)), and Bi/Pre-anodized SPCE containing NaBr (Bi/Pre-anodized SPCE(+ NaBr)) were used to detect Cd 2+ by SWASV. As shown in Fig. 4 , when Cd 2+ was detected by bare electrode, an irregular stripping peak of Cd 2+ appeared and the signal was weak. After modification of bismuth, the stripping peak shape of Cd 2+ is good and the peak height increased. In addition, the stripping peak of Bi 3+ was also observed at -0.42V, indicating that bismuth was successfully modified onto electrode through in-situ deposition. This result demonstrates that the co-deposition of Bi 3+ and Cd 2+ promotes the enrichment of Cd 2+ [ 26 ] . When Cd 2+ was detected using a Bi/Pre-anodized SPCE without NaBr, the stripping peak current of Cd 2+ increased significantly. The enhancement in Cd 2+ peak current benefits from the superior electron transfer ability of pre-anodization treatment. When a Bi/Pre-anodized SPCE containing NaBr was used, the highest stripping peak signal and the best peak shape of Cd 2+ was obtained, indicating good sensitization effect of NaBr, for that the complexation of Bi 3+ and Br - can improve the deposition of Bi on carbon-based electrode [ 27 , 28 ] . Taken together, benefited from co-deposition of Bi, pre-anodization activation and sensitization of NaBr, Bi/Pre-anodized SPCE containing NaBr demonstrated the best performance for Cd 2+ determination. 3.4 Optimization of experimental parameters In order to obtain the best detection effect of Bi/Pre-anodized SPCE for Cd 2+ determination, several experimental parameters including Bi 3+ concentration, NaBr concentration, electrolyte type, pH value of electrolyte, deposition potential and deposition time, stirring rate were studied. 3.4.1 Concentration of Bismuth and NaBr Firstly, the effect of Bi 3+ content on the stripping peak current of Cd 2+ was studied. As shown in Fig. 5 a, the peak current increases with gradual Bi 3+ concentration ranging from 0 to 150 µg/L, and reached a plateau at 150 µg/L. Therefore, Bi 3+ content of 150 µg/L was selected for subsequent experiments. Then, the influence of NaBr content on stripping peak current of Cd 2+ was explored. As shown in Fig. 5 b, the stripping peak current of Cd 2+ rose with the increased NaBr concentration ranging from 0 to 20 µmol/L, and kept relatively stable as the NaBr concentration rose continuously. Therefore, the optimal concentration of NaBr was 20 µmol/L. 3.4.2 Electrolyte types and pH values The influence of supporting electrolyte type and pH value on stripping peak signal of Cd 2+ was studied. Supporting electrolyte type was tested among 0.1 mol/L acetate buffer solution (ABS, pH = 4.5), phosphate buffer solution (PBS, pH = 7), HCl, NaOH and KCl. As shown in Fig. 5 c, the highest stripping peak current was obtained when using acetate buffer solution. Furthermore, 0.1mol/L acetate buffer solution with different pH values were investigated (Fig. 5 d). The optimal Cd 2+ stripping peak current was obtained when the pH of the acetate buffer solution is 4.5. Too low pH will easily lead to hydrogen evolution on the surface of working electrode and reduce the stripping response; Cd 2+ is prone to hydrolysis under high pH, resulting in a decrease in the stripping peak current [ 26 ] . Therefore, the electrolyte was selected as 0.1 mol/L acetate buffer solution with a pH of 4.5. 3.4.3 Deposition potential and deposition time The effects of deposition potential on the stripping peak current of Cd 2+ were investigated. As shown in Fig. 5 e, when the deposition potential moved from − 1.4 V to -1.8 V, hydrogen evolution was easy to occur under a low potential, and the hydrogen bubbles formed on the electrode surface hindered the stripping of Cd 2+ . Meanwhile, when the potential moved from − 1.4 V to -1.0 V, the enrichment of Cd 2+ was impaired for the deposition potential was close to the stripping potential of Cd 2+ , resulting in a decrease in stripping peak current. Therefore, the deposition potential was set as -1.4 V. Then, deposition time was investigated. The stripping peak current of Cd 2+ rose with the increase of deposition time, and presented a linear relationship after 120 s (Fig. 5 f), which is due to the adsorption balance of Cd 2+ between electrode surface and solution. Although increasing the deposition time can enhance stripping peak current and reduce the limit of detection, a longer time will prolong the detection period. Considering detection sensitivity as well as detection efficiency, the deposition time was set as 180 s. 3.4.4 Stirring rate Concentration polarization can be reduced by stirring during the deposition process, which is beneficial to the enrichment of Cd 2+ . The effect of stirring rate was investigated and adjusted by our self-made stirring device. As shown in Fig. S4, the stripping peak current increased significantly with the increase of stirring rate and reached a plateau at 200 rpm. Therefore, 200 rpm was used in the deposition process. 3.5 Analytical performance of Bi/Pre-anodized SPCE for Cd 2+ determination with portable potentiostat and stirring device Under optimal experimental conditions, the Bi/Pre-anodized SPCE (+ NaBr) was used to detect different concentrations of Cd 2+ through SWSV. The experiment was conducted on commercial potentiostat and portable PSoC Stat potentiostat, respectively. The PSoC Stat potentiostat was self-made according to a reported work and its published open-source program [ 29 ] . The main part of the device is PSoC 5LP single chip microcomputer (9.9 USD), and the detection resolution is improved by installing monolithic capacitor. In addition, a portable and low-cost stirring device was self-made for the electrochemical detection, which was fabricated by a time-delay relay (1.6 USD), a DC motor speed controller (0.7 USD), a motor (1.2USD), a sample cell (0.2 USD) and an SPCE connector (0.5 USD). The potentiostat was connected to the SPCE connector by dupont wire. The stripping curves using self-made PSoC Stat potentiostat were shown in Fig. 6 a. With the increase of Cd 2+ concentration, the stripping peak potential shifted towards positive potential direction, and the stripping peak current enhanced. The peak current showed a good linear relationship with Cd 2+ concentration in the range of 5 ~ 100 µg/L (Fig. 6 b). The linear regression equation was Ip = 0.29C + 0.35, and the lowest detection limit of Cd 2+ was 3.55 µg/L (S/N = 3). The stripping curves using commercial potentiostat were shown in Fig. S5a. The limit of detection reached 0.15 µg/L, and the linear range was 1 ~ 100 µg/L (Fig. S5b). Table 1 shows some reported electrochemical methods for Cd 2+ determination. It can be seen that compared with other methods, our proposed method demonstrates competitive sensitivity and linear range. More importantly, our method holds great advantage in the point-of-care testing (POCT). Although the limit of detection using self-made PSoC Stat potentiostat is higher than that using commercial potentiostat, it was lower than the maximum permissible level of Cd in drinking water (5 µg/L) [ 35 ] , which is sufficient for the on-site determination of Cd 2+ . In addition, the Bi/Pre-anodized SPCE can simultaneously determine Cd 2+ and Pb 2+ (Fig. S6), demonstrating the ability of multiple detection. Table 1 Comparison of different electrochemical sensors for Cd 2+ determination Electrode type Electrode modification Linear range (µg/L) LOD (µg/L) Instrument Ref. Carbon BOC 1 10 ~ 50 3.97 commercial [30] Screen-printed gold electrode Nafion-Bi 2 50 ~ 300 4 commercial [31] Carbon AgNP/Graphene/Nafion 3 25 ~ 250 25 commercial [32] SPCE Bismuth film 11.5 ~ 72.4 3.4 commercial [33] SPCE rGO/SMOF/PEI 4 56.3 ~ 1406.3 33.3 POCT [34] GC-SPE 5 Bismuth film 7.5 ~ 200 0.46 commercial [35] NC-BBD 6 Bismuth film 0 ~ 280 0.24 commercial [36] SPCE Bi PASPCE (+ NaBr) 1 ~ 100 0.15 commercial This work SPCE Bi PASPCE (+ NaBr) 5 ~ 100 3.55 POCT This work 1 BOC: Bismuth oxycarbide/nafion; 2 Nafion-Bi: in situ modification of bismuth and nafion; 3 AgNP: silver nanoparticles; 4 rGO/SMOF/PEI: graphene oxide /SMOF (composited by single wall carbon nanotube and UiO-66-NH 2 MOF) /polyethyleneimine; 5 GC-SPE: glassy carbon microparticle stencil printed electrode; 6 NC-BBD: nitrogen rich porous carbon/boron doped diamond composite electrode. The repeatability of the proposed electrode for Cd 2+ determination was evaluated by 10 consecutive tests of 50 µg/L Cd 2+ standard solution (Fig. 6 c). The relative standard deviation (RSD) of the measured peak current values was 4.4%, which indicates a good repeatability. Moreover, considering the interference from other potential metal ions in the determination of Cd 2+ in actual samples, the anti-interference ability of Bi/Pre-anodized SPCE was studied. Ca 2+ , Mg 2+ , Hg 2+ , Fe 3+ and K + with a concentration 10 times higher than that of Cd 2+ , as well as a similar concentration of Pb 2+ and Cu 2+ was added to the supporting electrolyte containing 50 µg/L Cd 2+ as interfering ion, respectively. As shown in Fig. 6 d, Ca 2+ , Mg 2+ , Fe 3+ , K + and Pb 2+ had little interference on the determination of Cd 2+ , while Cu 2+ significantly reduced the stripping peak current of Cd 2+ . This inhibition may be due to the competition between Bi 3+ and Cu 2+ for the active site on the working electrode during deposition as well as the formation of intermetallic compounds among copper and cadmium [ 37 ] . The interference from Cu 2+ can be eliminated by the addition of 40 µmol/L potassium ferrocyanide into the detection solution (Fig. 6 d). 3.6 Recovery studies To assess the feasibility of the developed heavy metal electrochemical sensor in practical applications, a spike-recovery method was used to detect Cd 2+ in tap water and rice extract. The pre-treatment of tap water and rice samples were described in 2.4. The spiked amount of Cd 2+ were set to four different levels. Each spiked sample was measured three times in parallel. Simultaneously, the spiked samples were determined by ICP-MS. Table 2 Results of Cd 2+ determination in tap water and rice samples using PSoC Stat potentiostat Sample Spiked (µg/L) Found (µg/L) Recovery rate (%) RSD* (%) Found by ICP-MS (µg/L) |Error| 0 10 - 10.7 107.1 - 3.27 - 10.3 - 3.9% Tap water 30 27.5 91.7 4.68 29.4 6.4% 60 57.1 95.2 2.94 60.8 6.1% 0 10 - 9.2 - 92.3 - 3.74 - 9.8 - 6.1% Rice 30 31.1 103.7 2.09 32.4 4.0% 60 61.9 103.2 5.26 63.0 1.7% * Relative standard deviation. For each concentration, three replicates were measured. As shown in Table 2 , when using our proposed electrochemical sensor, the recoveries in water and rice samples ranged from 91.7–107.1%, and the RSD were between 2.09% and 5.26%. In addition, the detection results were consistent with ICP-MS with deviation below 10%. These results demonstrate that the heavy metal electrochemical sensor owns great accuracy and reliability, and can be applied to the determination of Cd 2+ in tap water and rice samples. 4. Conclusion A metal-bismuth modified pre-anodized screen-printed electrode was prepared based on the pre-anodization and in-situ deposition technique. Various electrochemical characteristics proved the successful preparation of the modified electrode. Benefiting from pre-anodization, bismuth co-deposition and bromine sensitization, the electron transfer ability was improved, the enrichment of Cd 2+ was facilitated, and the sensitivity of the electrode for Cd 2+ determination was significantly enhanced. Coupled with the self-made, portable and low-cost potentiostat and stirring device, the electrochemical sensor has a wide linear range of 5 ~ 100 µg/L and a low detection limit of 3.55 µg/L, possesses good repeatability and specificity. In addition, it can be applied to the determination of Cd 2+ in drinking water and rice. Our work provides a promising electrode fabrication method and a point of need device for electrochemical determination of heavy metals. Declarations CRediT authorship Contribution statement Yongfang Li: Conceptualization, Methodology, Formal analysis, Data curation, Writing-original draft, Funding acquisition; Zijun Wang: Methodology, Investigation, Data curation, Writing-review and editing; Xuan Chen: Methodology, Validation, Data curation, Writing-review and editing; Zhijian Yi: Methodology, Software, Data curation, Writing-review and editing; Rui Wang: Validation, Resources, Writing-review and editing, Visualization, Supervision, Project administration, Funding acquisition. Declaration of Competing Interest The authors declare no competing interests. Acknowledgment This research was funded by start-up funds for scientific research of high-level talents in Foshan University and the National Natural Science Foundation of China (32371521). Data availability The datasets used and analyzed during the current study are available from the corresponding author on reasonable request. References Fatima, G., Raza, A. 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Microchim. Acta 184, 4731-4740(2017). Gong, Q., et al. Sensitive electrochemical DNA sensor for the detection of HIV based on a polyaniline/graphene nanocomposite. JMAT . 5, 313-319(2019). Lu, Y. Y., et al. A review of the identification and detection of heavy metal ions in the environment by voltammetry. Talanta . 178, 324-338(2018). Zidarič T., et al. Multi-pulse galvanostatic preparation ofnanostructured bismuth film electrode for trace metal detection. Sensor Actuat. B 245 , 720-725(2017). Królicka A., Bobrowski A. Bismuth film electrode for adsorptive stripping voltammetry–electrochemical and microscopic study. Electrochem. Commun . 6 (2), 99-104(2004). Lopin, P., Lopin, K. V. PSoC-Stat: A single chip open source potentiostat based on a programmable system on a chip. PLoS One 13, e0201353(2018). Zhang, Y., Li, C., Su, Y., Mu, W., Han, X. Simultaneous detection of trace Cd(II) and Pb(II) by differential pulse anodic stripping voltammetry using a bismuth oxycarbide/nafion electrode. Inorg. Chem. Commun . 111 (2020). Albalawi, I., Hogan, A., Alatawi, H., Moore, E. A sensitive electrochemical analysis for cadmium and lead based on Nafion-Bismuth film in a water sample. S ens. B io -S ens. R es. 34, 100454(2021). Palisoc, S., Gallardo, A., Laurito, C., Natividad, M. Determination of heavy metals in corn (Zea mays L.) using silver nanoparticles/graphene/nafion modified glassy carbon electrode. Agronomy Research 18, 2185-2196(2020). Sosa, V., et al. Antimony film screen-printed carbon electrode for stripping analysis of Cd(II), Pb(II), and Cu(II) in natural samples. Anal. Chim. Acta 855, 34-40(2015). Xu, Z. Z., Liu, Z. J., Xiao, M., Jiang, L. L., Yi, C. Q. A smartphone-based quantitative point-of-care testing (POCT) system for simultaneous detection of multiple heavy metal ions. Chem. Eng. J . 394, 124966(2020). Kava, A.A.; Beardsley, C.; Hofstetter, J.; Henry, C.S. Disposable glassy carbon stencil printed electrodes for trace detection of cadmium and lead. Anal. Chim. Acta 1103, 58-66(2020). Zhou, X., et al. High performance ratiometric detection towards trace Cd(II) and Pb(II) utilizing in-situ bismuth modified nitrogen rich porous carbon/boron doped diamond composite electrode. J. Environ. Chem. Eng . 11 (2023). Saeed, A. A., Singh, B., Abbas, M. N., Dempsey, E. Evaluation of bismuth modified carbon thread electrode for simultaneous and highly sensitive Cd (II) and Pb (II) determination. Electroanal. 28, 2205-2213(2016). Additional Declarations No competing interests reported. Supplementary Files SupportingInformation.docx Cite Share Download PDF Status: Published Journal Publication published 08 Aug, 2024 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 09 Jul, 2024 Reviews received at journal 05 Jul, 2024 Reviewers agreed at journal 25 Jun, 2024 Reviews received at journal 25 Jun, 2024 Reviewers agreed at journal 25 Jun, 2024 Reviewers invited by journal 24 Jun, 2024 Editor assigned by journal 24 Jun, 2024 Editor invited by journal 21 Jun, 2024 Submission checks completed at journal 19 Jun, 2024 First submitted to journal 18 Jun, 2024 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. 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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-4600103","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":323143225,"identity":"8746011b-74ad-4590-a3b4-13075725273b","order_by":0,"name":"Yongfang Li","email":"","orcid":"","institution":"Foshan University","correspondingAuthor":false,"prefix":"","firstName":"Yongfang","middleName":"","lastName":"Li","suffix":""},{"id":323143226,"identity":"32e781c4-0fe9-4694-8b06-a981bba3574b","order_by":1,"name":"Zijun Wang","email":"","orcid":"","institution":"Foshan University","correspondingAuthor":false,"prefix":"","firstName":"Zijun","middleName":"","lastName":"Wang","suffix":""},{"id":323143227,"identity":"58fc72c7-3c62-41cf-8b1f-bc4b37bf68ff","order_by":2,"name":"Xuan Chen","email":"","orcid":"","institution":"Foshan University","correspondingAuthor":false,"prefix":"","firstName":"Xuan","middleName":"","lastName":"Chen","suffix":""},{"id":323143228,"identity":"e6fdcd71-0c02-4e69-bd31-d8e32fa08da8","order_by":3,"name":"Zhijian Yi","email":"","orcid":"","institution":"Foshan University","correspondingAuthor":false,"prefix":"","firstName":"Zhijian","middleName":"","lastName":"Yi","suffix":""},{"id":323143229,"identity":"91a7926d-1faf-4f29-b244-9007da610539","order_by":4,"name":"Rui Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0klEQVRIiWNgGAWjYNCCCjkGhgMgBhvRWs4Yk6qFsY0ULQbHzx5+XTnPILHv+NkDDB/KDjPwz24goOVMXprl2W0GiTPP5CUwzjh3mEHizgH8WswO5JgZNm77k7jhQI4BM2/bYQYDiQQCWs6/AWqZY5C44fwbA+a/RGm5kWP8sLEBqOUG0BZGYrTY33hjxthwzMB45o03Bgd7zqXzSNwgoEWyP8f4Y0ONgWzf+RzDBz/KrOX4ZxDQAgRsEjDWASDmIageCJg/EKNqFIyCUTAKRjAAAO6HSajbxkG9AAAAAElFTkSuQmCC","orcid":"","institution":"Fudan University","correspondingAuthor":true,"prefix":"","firstName":"Rui","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2024-06-18 12:51:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4600103/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4600103/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-024-69626-7","type":"published","date":"2024-08-08T15:57:02+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":59834466,"identity":"2e4eb4d8-eb5b-44ea-b04e-4f950784c240","added_by":"auto","created_at":"2024-07-08 08:14:23","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":266837,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of Cd\u003csup\u003e2+\u003c/sup\u003e determination with in-situ bismuth modified pre-anodized SPCE and portable device. The stirring device contains an SPCE connector, a sample cell and a time- and speed-regulated stirring motor. The self-made PSoC Stat potentiostat connects to SPCE connector by dupont wire. The SPCE was pre-anodized in PBS (pH=9) by cyclic voltammetry to active its surface. Then Bi\u003csup\u003e3+\u003c/sup\u003e and Cd\u003csup\u003e2+\u003c/sup\u003e were co-deposited on pre-anodized electrode, and Cd\u003csup\u003e2+\u003c/sup\u003e was stripped out for determination. The stirring function is applied in the deposition process.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-4600103/v1/b1c23a1de8647ef8187bd137.png"},{"id":59835060,"identity":"66418252-37cf-43df-8c3e-d250459c2af1","added_by":"auto","created_at":"2024-07-08 08:22:23","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":431615,"visible":true,"origin":"","legend":"\u003cp\u003eOptimization of pre-anodization conditions. (a) CV curves of SPCE pre-anodized in different solutions. (b) CV curves of SPCE pre-anodized in PBS with different pH. (c) CV curves of SPCE treated with different scanning turns. (d) The relationship between the number of scanning cycles and redox current values.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-4600103/v1/fc6539b2735bc46da67bfcb2.png"},{"id":59834464,"identity":"7ff4ea6f-08e5-4456-a69d-19330bfec73c","added_by":"auto","created_at":"2024-07-08 08:14:23","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":428393,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Cyclic voltammetry curves of pre-anodized SPCE at different scanning rates. (b) The relationship between redox peak current value and the square root of scanning rate. Cyclic voltammetry curves (c) and Electrochemical impedance spectroscopy curves (d) of screen-printed electrode with different modifications.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-4600103/v1/57ada6195beea3ac2b36167a.png"},{"id":59834030,"identity":"c1488f05-37f6-4061-93b2-5c8f57235cf1","added_by":"auto","created_at":"2024-07-08 08:06:23","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":103632,"visible":true,"origin":"","legend":"\u003cp\u003eSquare wave stripping voltammetry curves of Cd\u003csup\u003e2+\u003c/sup\u003e with different electrodes.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-4600103/v1/a28b8f9dc154c8b7e799a62d.png"},{"id":59834031,"identity":"cc9a00c2-81fc-4860-b675-08ada0faff3e","added_by":"auto","created_at":"2024-07-08 08:06:24","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":246791,"visible":true,"origin":"","legend":"\u003cp\u003eOptimization of experimental parameters for Cd\u003csup\u003e2+\u003c/sup\u003e determination. (a) Bi\u003csup\u003e3+\u003c/sup\u003e content. (b) NaBr content. (c) Supporting electrolyte. (d) ABS with different pH. (e) Deposition potential. (f) Deposition time.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-4600103/v1/5c111d84e6c1336be8c2a680.png"},{"id":59834029,"identity":"4ee37ce5-33c6-464f-aa38-8d63a481715c","added_by":"auto","created_at":"2024-07-08 08:06:23","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":259218,"visible":true,"origin":"","legend":"\u003cp\u003eAnalytical performance of in-situ bismuth modified pre-anodized SPCE for Cd\u003csup\u003e2+ \u003c/sup\u003edetermination with self-made PSoC Stat potentiostat and stirring device. (a) The square wave anodic stripping curves of Cd\u003csup\u003e2+\u003c/sup\u003e. (b) The relationship between stripping peak current values and Cd\u003csup\u003e2+\u003c/sup\u003e concentrations. Error bars represent the standard deviations calculated from three separate experiments. (c) Reproducibility of developed sensor for Cd\u003csup\u003e2+\u003c/sup\u003e detection at the concentration of 50 μg/L. Ten measurements were conducted repeatedly. (d) Specificity evaluation of the electrochemical sensor. The interfering ion was added to the Cd\u003csup\u003e2+\u003c/sup\u003e solution separately, and the corresponding peak current values of Cd\u003csup\u003e2+\u003c/sup\u003e were compared with that of Cd\u003csup\u003e2+\u003c/sup\u003e solution absent of any different ions (marked as Absence).\u0026nbsp;\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-4600103/v1/5760abd5db148274a630e464.png"},{"id":62298195,"identity":"fd273012-66fc-47f8-ac50-cfca81c90cec","added_by":"auto","created_at":"2024-08-12 16:10:02","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2504786,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4600103/v1/1d8a6c95-68b7-4afa-b475-0a84b00992fa.pdf"},{"id":59834025,"identity":"ebf92a96-348e-471b-a2bc-dc31963ae670","added_by":"auto","created_at":"2024-07-08 08:06:23","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":855524,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-4600103/v1/6285c272446b2a9e648e389a.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"In situ deposition of bismuth on pre-anodized screen-printed electrode for sensitive determination of Cd2+ in water and rice with a portable device","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eCadmium (Cd) is a toxic heavy metal that has multiple toxic effects on the human kidney, liver, nervous and cardiovascular systems\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e. With the increase of industrial activities such as smelting operations, electroplating, pigments, fertilizers and mining, a large amount of industrial wastewater containing cadmium was discharged without treatment, seriously polluting drinking water and soil\u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. The consumption of cadmium-contaminated water and rice poses a great threat to human health\u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e. Therefore, sensitive and rapid determination of cadmium in food is of great significance for environmental protection and food safety.\u003c/p\u003e \u003cp\u003eConventional methods for cadmium detection include atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS) and inductively coupled plasma mass spectrometry (ICP-MS)\u003csup\u003e[\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e. Although these methods possess high sensitivity, accuracy and stability, they need complex instrument operation, long operation time and high operating cost, which are not suitable for rapid field detection\u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e. Anodic stripping voltammetry is considered as a powerful tool for heavy metal detection \u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e. In this method, Cd\u003csup\u003e2+\u003c/sup\u003e is enriched to the electrode surface at a constant potential and reduced to Cd\u003csup\u003e0\u003c/sup\u003e. Then Cd\u003csup\u003e0\u003c/sup\u003e is oxidized to Cd\u003csup\u003e2+\u003c/sup\u003e under scanning voltage and stripped out into the electrolyte to generate a current. The current value is proportional to the content of metal ions, and each metal ion has its characteristic oxidation potential\u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eElectrode modification is an important means to improve the analytical sensitivity of electrochemical sensors. Bismuth modified electrode has been widely used for Cd determination and the simultaneous determination of Cd, Pb and Zn\u003csup\u003e[\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e. The modification of bismuth can be finished by in-situ deposition, ex-situ deposition or dropping ways\u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e. In-situ deposition owns great advantage for that the co-deposition of Bi\u003csup\u003e3+\u003c/sup\u003e and Cd\u003csup\u003e2+\u003c/sup\u003e can enhance the enrichment of Cd\u003csup\u003e2+\u003c/sup\u003e, thus improving the detection sensitivity\u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e. Besides, in-situ deposition is easy handling and time-saving, avoids the risk of degradation and uneven distribution of modified bismuth\u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e. Except for metal material modification, electrochemical activation can also enhance the detection sensitivity of electrode \u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. Pre-anodization is an effective method for electrode activation by accelerating the electron transfer between substance and electrode\u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e. It owns the characteristics of less reagent and simple operation\u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e. Moreover, to achieve point-of-need quantitation of heavy metal Cd\u003csup\u003e2+\u003c/sup\u003e, a portable and low-cost device capable of transmitting, collecting and displaying electrochemical signals is urgently required.\u003c/p\u003e \u003cp\u003eHerein, by combining pre-anodization technique and in-situ deposition method, an in-situ bismuth modified pre-anodized screen-printed carbon electrode (Bi/Pre-anodized SPCE) for Cd\u003csup\u003e2+\u003c/sup\u003e determination was prepared, and the detection was conducted on a portable, self-made and low-cost potentiostat coupled with a stirring device (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The pre-anodization was carried out in PBS (pH\u0026thinsp;=\u0026thinsp;9) by cyclic voltammetry (CV) method. Then Bi\u003csup\u003e3+\u003c/sup\u003e and Cd\u003csup\u003e2+\u003c/sup\u003e were co-deposited on the pre-anodized electrode and Cd\u003csup\u003e2+\u003c/sup\u003e was stripped out for determination by square wave anodic stripping voltammetry (SWASV). The developed electrochemical sensor demonstrated good performance for Cd\u003csup\u003e2+\u003c/sup\u003e determination with limit of detection as low as 0.15 \u0026micro;g/L and 3.55 \u0026micro;g/L using commercial and self-made potentiostat, respectively. The test could be completed within 3 min with good repeatability and specificity. The recovery rates in water and rice samples ranged from 91.7\u0026ndash;107.1%.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Reagents and materials\u003c/h2\u003e \u003cp\u003eSodium acetate, sodium bromide, acetic acid and hydrogen peroxide were purchased from Guangzhou Chemical Reagent Factory. K\u003csub\u003e3\u003c/sub\u003e[Fe (CN\u003csub\u003e6\u003c/sub\u003e)] and K\u003csub\u003e4\u003c/sub\u003e[Fe (CN)\u003csub\u003e6\u003c/sub\u003e] were purchased from Shanghai Maclin Biochemical Technology Co., LtD. The 0.22 \u0026micro;m filter membrane was purchased from Beekman Biological Corporation. Stock solution of bismuth ion and cadmium ion (1000 \u0026micro;g/mL) were purchased from Beijing General Research Institute of Non-Ferrous Metals. Screen-printed carbon electrode (diameter 2.8mm) was obtained from Wuhan Zhongke Zhikang Biotechnology Co., LtD. All solutions were prepared using ultrapure water produced by Milli-Q ultrapure water (Millipore Company, USA).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Instruments\u003c/h2\u003e \u003cp\u003eScanning electron microscope (SEM) images were acquired on a a field emission scanning electron microscope (Quattro S, Thermo Fisher Scientific, USA). Energy dispersive X-ray (EDX) spectrum was collected on an energy dispersive spectrometer (Ultim Max Oxford Instruments LtD., U.K.). Electrochemical impedance spectroscopy (EIS) was performed with a potentiostat (Autolab 302N, Metrohm Autolab B.V., Switzerland). Other electrochemical measurements were performed on a CHI1440 constant potential instrument (Shanghai Chenhua Instrument Co., LtD.) and a self-made PSoC Stat potentiostat (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). A stirring device containing an SPCE connector, a sample cell and a time- and speed-regulated stirring motor was self-made for the experiment (Fig. S2).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Experimental methods\u003c/h2\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.3.1 Pre-anodization of screen-printed carbon electrode\u003c/h2\u003e \u003cp\u003eThe screen-printed electrode was pre-anodized by cyclic voltammetry method. The SPCE was scanned for 5 cycles in 0.1 mol/L PBS phosphate buffer solution (pH\u0026thinsp;=\u0026thinsp;9), with a scanning range of 0.5\u0026thinsp;~\u0026thinsp;1.7 V and a scanning rate of 0.1 V/s. Then the SPCE was rinsed thoroughly with ultra-pure water and dried at room temperature.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.3.2 SWASV for Cd\u003csup\u003e2+\u003c/sup\u003e determination\u003c/h2\u003e \u003cp\u003e1 mL of 0.1 mol /L acetate buffer (pH 4.5) containing 150 \u0026micro;g/L Bi\u003csup\u003e3+\u003c/sup\u003e, 20 \u0026micro;mol/L NaBr and a certain concentration of Cd\u003csup\u003e2+\u003c/sup\u003e were added into the sample cell. Then the pre-anodized SPCE were immersed into the solution. The detection parameters of SWSV were set as follows: deposition potential is -1.4 V, deposition time is 180 s, potential increment is 4 mV, amplitude is 25 Hz, scanning range is -1.4~ -0.2 V. In the deposition process, the sample cell was rotated by the stirring motor with a stirring rate of 200 rpm. No stirring was provided in the stripping process. All tests were performed at room temperature (26\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 \u0026deg; C).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Recovery study\u003c/h2\u003e \u003cp\u003eTap water and rice samples without Cd were selected for recovery studies. The rice samples were purchased from a local market in Foshan. The tap water was filtered by 0.22 \u0026micro;m microporous filter membrane. Filtered water was adjusted to pH 4.5 by nitric acid, then mixed with an equal volume of 0.2 mol/L acetate buffer solution (pH\u0026thinsp;=\u0026thinsp;4.5) to obtain the pre-treated tap water sample.\u003c/p\u003e \u003cp\u003eThe pretreatment of rice samples was referred to the method reported by Wang \u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e. The rice samples were crushed into powder and dried in an oven for 2 hours. 1 g rice powder was dissolved in 10 mL nitric acid and boiled until nearly dry. Then 3 mL H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was added and heated until dry. The residue was dissolved in 25 mL 0.1mol /L acetic acid. After complete vortex oscillation, the solution was filtered by 0.22 \u0026micro;m membrane. The filtrate was adjusted to pH 4.5 by NaOH solution to obtain the pre-treated rice extract.\u003c/p\u003e \u003cp\u003eStandard solution of Cd\u003csup\u003e2+\u003c/sup\u003ewere added into the pre-treated tap water or rice extract. Then the spiked samples were analyzed by both the established electrochemical method described in 2.3.2 and ICP-MS.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Study of electrode pre-anodization\u003c/h2\u003e \u003cp\u003eThe effect of solution type on pre-anodization was firstly evaluated. The screen-printed electrode was pre-anodized with 0.1 mol/L HNO\u003csub\u003e3\u003c/sub\u003e, HCl, H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, NaOH, PBS (pH\u0026thinsp;=\u0026thinsp;5), PBS (pH\u0026thinsp;=\u0026thinsp;7) and PBS (pH\u0026thinsp;=\u0026thinsp;9), respectively. Then the electrochemical characteristics of the electrodes were evaluated by cyclic voltammetry in 5 mmol/L [Fe (CN)\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e3\u0026minus;/4\u0026minus;\u003c/sup\u003e containing 0.1 mol/L KCl. The scanning range was \u0026minus;\u0026thinsp;0.5\u0026thinsp;~\u0026thinsp;0.7 V, the scanning rate was 0.1 V/s. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, compared with HNO\u003csub\u003e3\u003c/sub\u003e, HCl, H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and NaOH, the highest redox current and smallest peak potential difference were obtained when using 0.1 mol/L PBS (pH\u0026thinsp;=\u0026thinsp;9), indicating an excellent electron transfer ability. Subsequently, PBS solution with different pH values were compared. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, PBS (pH\u0026thinsp;=\u0026thinsp;9) demonstrated the best performance. In addition, compared with bare electrode, pre-anodization definitely improves the electron transfer ability.\u003c/p\u003e \u003cp\u003eNext, the effect of scanning turns in pre-anodization was studied. SPCE was pre-anodized in 0.1 mol/L PBS solution (pH\u0026thinsp;=\u0026thinsp;9) for different scanning cycles, then the SPCEs were characterized by CV in 5 mmol/L [Fe (CN)\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e3\u0026minus;/4\u0026minus;\u003c/sup\u003e containing 0.1 mol/L KCl. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, as the number of scanning cycles varies from 0 to 5, the redox current increases significantly and the peak potential difference decreases markedly. When the number of scanning turns exceeds 5, the peak potential difference is basically unchanged and the redox current decreases slightly (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). Therefore, scanning turn was set as 5 in the pre-anodization of SPCE.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Morphological characterization and element analysis of SPCE\u003c/h2\u003e \u003cp\u003eSEM and EDX were used to characterize the surface of SPCE during modification process. As shown in Fig. S3a-c, pre-anodization and bismuth modification have little effect on the morphology of the electrode surface. Since pre-anodization treatment has a good activation effect on the SPCE, it indicates that the main mechanism of activating the SPCE by pre-anodization is not through cleaning the electrode or other factors that cause great changes in the morphology of the electrode. The in-situ deposited bismuth cannot be observed directly through SEM images, however, EDX spectrum demonstrates the existence of Bi on the surface of SPCE (Fig. S3d). It is attributed to the small size and low content of bismuth. Therefore, the pre-anodized and bismuth modified electrodes will be further characterized by electrochemical methods.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Electrochemical characterization of SPCE\u003c/h2\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.3.1 Electrode performance evaluation with cyclic voltammetry\u003c/h2\u003e \u003cp\u003ePre-anodized SPCE was characterized by cyclic voltammetry in 5 mmol/L [Fe (CN)6]\u003csup\u003e3\u0026minus;/4\u0026minus;\u003c/sup\u003e and 0.1 mol/L KCl solution at different scanning rates. The scanning range is -0.5\u0026thinsp;~\u0026thinsp;0.7 V, the scanning rate is 0.05\u0026thinsp;~\u0026thinsp;0.3 V/s. The redox peak current enhanced with the increasing scanning rate (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). Ipa and Ipc were linearly correlated with the square root of scan rate (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb), indicating that the redox process is mainly based on diffusion-controlled reactions \u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThen different electrodes were evaluated by cyclic voltammetry with scanning rate set as 0.1 V /s. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, compared with bare electrode, the redox current increased significantly and the peak potential difference decreased after pre-anodization. On this basis, in situ deposition of metallic bismuth further improves the peak current. In addition, the presence of NaBr in bismuth modification enhanced the peak current. The EIS result was consistent with the CV test for that the Rct decreased with the electrode modification (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). This suggests that pre-anodization and bismuth modification improve the charge transfer rate of screen-printed electrode \u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eFurthermore, the effective area of the electrode was calculated by Randles-Sevcik equation\u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e. The equation is shown in (1).\u003c/p\u003e \u003cp\u003e \u003cem\u003eI\u003c/em\u003e \u003csub\u003eP\u003c/sub\u003e=2.69\u0026times;10\u003csup\u003e5\u003c/sup\u003en\u003csup\u003e3/2\u003c/sup\u003e\u003cem\u003eAD\u003c/em\u003e\u003csup\u003e1/2\u003c/sup\u003e \u003cem\u003ev\u003c/em\u003e \u003csup\u003e1/2\u003c/sup\u003e\u003cem\u003eC\u003c/em\u003e (1)\u003c/p\u003e \u003cp\u003e \u003cem\u003eI\u003c/em\u003ep is the redox peak current (A), \u003cem\u003en\u003c/em\u003e is the number of transferred electrons (n\u0026thinsp;=\u0026thinsp;1), A is the active surface area of working electrode (cm\u003csup\u003e2\u003c/sup\u003e), D is the diffusion coefficient of electroactive substance (cm\u003csup\u003e2\u003c/sup\u003e/s), \u003cem\u003eC\u003c/em\u003e is the concentration of electroactive substance (mol/cm\u003csup\u003e3\u003c/sup\u003e) and \u003cem\u003ev\u003c/em\u003e is the scan rate (V/s). For 5 mmol/L of [Fe (CN)\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e3\u0026minus;/4\u0026minus;\u003c/sup\u003e, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1, and \u003cem\u003eD\u003c/em\u003e\u0026thinsp;=\u0026thinsp;6.30\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003ecm\u003csup\u003e2\u003c/sup\u003e/s. After calculation, the effective area of pre-anodized SPCE (0.057 cm\u003csup\u003e2\u003c/sup\u003e) is about 2.59 times that of the bare electrode (0.022 cm\u003csup\u003e2\u003c/sup\u003e), and further increased after the in-situ deposition of bismuth, reaching 0.064 cm\u003csup\u003e2\u003c/sup\u003e (without NaBr) and 0.078 cm\u003csup\u003e2\u003c/sup\u003e (with NaBr), respectively. The results demonstrated that the active surface area of the screen-printed electrode is enlarged by pre-anodization and bismuth modification, which is beneficial to improve the sensitivity of the electrochemical sensor.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.3.2 Electrochemical response of different electrodes towards Cd\u003csup\u003e2+\u003c/sup\u003e\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eBare SPCE, in situ bismuth modified electrode (Bi-SPCE), Bi/Pre-anodized SPCE without NaBr (Bi/Pre-anodized SPCE (-NaBr)), and Bi/Pre-anodized SPCE containing NaBr (Bi/Pre-anodized SPCE(+\u0026thinsp;NaBr)) were used to detect Cd\u003csup\u003e2+\u003c/sup\u003e by SWASV. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, when Cd\u003csup\u003e2+\u003c/sup\u003e was detected by bare electrode, an irregular stripping peak of Cd\u003csup\u003e2+\u003c/sup\u003e appeared and the signal was weak. After modification of bismuth, the stripping peak shape of Cd\u003csup\u003e2+\u003c/sup\u003e is good and the peak height increased. In addition, the stripping peak of Bi\u003csup\u003e3+\u003c/sup\u003e was also observed at -0.42V, indicating that bismuth was successfully modified onto electrode through in-situ deposition. This result demonstrates that the co-deposition of Bi\u003csup\u003e3+\u003c/sup\u003e and Cd\u003csup\u003e2+\u003c/sup\u003e promotes the enrichment of Cd\u003csup\u003e2+ [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e. When Cd\u003csup\u003e2+\u003c/sup\u003e was detected using a Bi/Pre-anodized SPCE without NaBr, the stripping peak current of Cd\u003csup\u003e2+\u003c/sup\u003e increased significantly. The enhancement in Cd\u003csup\u003e2+\u003c/sup\u003e peak current benefits from the superior electron transfer ability of pre-anodization treatment. When a Bi/Pre-anodized SPCE containing NaBr was used, the highest stripping peak signal and the best peak shape of Cd\u003csup\u003e2+\u003c/sup\u003e was obtained, indicating good sensitization effect of NaBr, for that the complexation of Bi\u003csup\u003e3+\u003c/sup\u003e and Br\u003csup\u003e-\u003c/sup\u003e can improve the deposition of Bi on carbon-based electrode \u003csup\u003e[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e. Taken together, benefited from co-deposition of Bi, pre-anodization activation and sensitization of NaBr, Bi/Pre-anodized SPCE containing NaBr demonstrated the best performance for Cd\u003csup\u003e2+\u003c/sup\u003e determination.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Optimization of experimental parameters\u003c/h2\u003e \u003cp\u003eIn order to obtain the best detection effect of Bi/Pre-anodized SPCE for Cd\u003csup\u003e2+\u003c/sup\u003e determination, several experimental parameters including Bi\u003csup\u003e3+\u003c/sup\u003e concentration, NaBr concentration, electrolyte type, pH value of electrolyte, deposition potential and deposition time, stirring rate were studied.\u003c/p\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.4.1 Concentration of Bismuth and NaBr\u003c/h2\u003e \u003cp\u003eFirstly, the effect of Bi\u003csup\u003e3+\u003c/sup\u003e content on the stripping peak current of Cd\u003csup\u003e2+\u003c/sup\u003e was studied. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, the peak current increases with gradual Bi\u003csup\u003e3+\u003c/sup\u003e concentration ranging from 0 to 150 \u0026micro;g/L, and reached a plateau at 150 \u0026micro;g/L. Therefore, Bi\u003csup\u003e3+\u003c/sup\u003e content of 150 \u0026micro;g/L was selected for subsequent experiments. Then, the influence of NaBr content on stripping peak current of Cd\u003csup\u003e2+\u003c/sup\u003e was explored. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb, the stripping peak current of Cd\u003csup\u003e2+\u003c/sup\u003e rose with the increased NaBr concentration ranging from 0 to 20 \u0026micro;mol/L, and kept relatively stable as the NaBr concentration rose continuously. Therefore, the optimal concentration of NaBr was 20 \u0026micro;mol/L.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e3.4.2 Electrolyte types and pH values\u003c/h2\u003e \u003cp\u003eThe influence of supporting electrolyte type and pH value on stripping peak signal of Cd\u003csup\u003e2+\u003c/sup\u003e was studied. Supporting electrolyte type was tested among 0.1 mol/L acetate buffer solution (ABS, pH\u0026thinsp;=\u0026thinsp;4.5), phosphate buffer solution (PBS, pH\u0026thinsp;=\u0026thinsp;7), HCl, NaOH and KCl. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec, the highest stripping peak current was obtained when using acetate buffer solution. Furthermore, 0.1mol/L acetate buffer solution with different pH values were investigated (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). The optimal Cd\u003csup\u003e2+\u003c/sup\u003e stripping peak current was obtained when the pH of the acetate buffer solution is 4.5. Too low pH will easily lead to hydrogen evolution on the surface of working electrode and reduce the stripping response; Cd\u003csup\u003e2+\u003c/sup\u003e is prone to hydrolysis under high pH, resulting in a decrease in the stripping peak current \u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e. Therefore, the electrolyte was selected as 0.1 mol/L acetate buffer solution with a pH of 4.5.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003e3.4.3 Deposition potential and deposition time\u003c/h2\u003e \u003cp\u003eThe effects of deposition potential on the stripping peak current of Cd\u003csup\u003e2+\u003c/sup\u003e were investigated. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee, when the deposition potential moved from \u0026minus;\u0026thinsp;1.4 V to -1.8 V, hydrogen evolution was easy to occur under a low potential, and the hydrogen bubbles formed on the electrode surface hindered the stripping of Cd\u003csup\u003e2+\u003c/sup\u003e. Meanwhile, when the potential moved from \u0026minus;\u0026thinsp;1.4 V to -1.0 V, the enrichment of Cd\u003csup\u003e2+\u003c/sup\u003e was impaired for the deposition potential was close to the stripping potential of Cd\u003csup\u003e2+\u003c/sup\u003e, resulting in a decrease in stripping peak current. Therefore, the deposition potential was set as -1.4 V.\u003c/p\u003e \u003cp\u003eThen, deposition time was investigated. The stripping peak current of Cd\u003csup\u003e2+\u003c/sup\u003e rose with the increase of deposition time, and presented a linear relationship after 120 s (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef), which is due to the adsorption balance of Cd\u003csup\u003e2+\u003c/sup\u003e between electrode surface and solution. Although increasing the deposition time can enhance stripping peak current and reduce the limit of detection, a longer time will prolong the detection period. Considering detection sensitivity as well as detection efficiency, the deposition time was set as 180 s.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e \u003ch2\u003e3.4.4 Stirring rate\u003c/h2\u003e \u003cp\u003eConcentration polarization can be reduced by stirring during the deposition process, which is beneficial to the enrichment of Cd\u003csup\u003e2+\u003c/sup\u003e. The effect of stirring rate was investigated and adjusted by our self-made stirring device. As shown in Fig. S4, the stripping peak current increased significantly with the increase of stirring rate and reached a plateau at 200 rpm. Therefore, 200 rpm was used in the deposition process.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Analytical performance of Bi/Pre-anodized SPCE for Cd\u003csup\u003e2+\u003c/sup\u003e determination with portable potentiostat and stirring device\u003c/h2\u003e \u003cp\u003eUnder optimal experimental conditions, the Bi/Pre-anodized SPCE (+\u0026thinsp;NaBr) was used to detect different concentrations of Cd\u003csup\u003e2+\u003c/sup\u003e through SWSV. The experiment was conducted on commercial potentiostat and portable PSoC Stat potentiostat, respectively. The PSoC Stat potentiostat was self-made according to a reported work and its published open-source program\u003csup\u003e[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]\u003c/sup\u003e. The main part of the device is PSoC 5LP single chip microcomputer (9.9 USD), and the detection resolution is improved by installing monolithic capacitor. In addition, a portable and low-cost stirring device was self-made for the electrochemical detection, which was fabricated by a time-delay relay (1.6 USD), a DC motor speed controller (0.7 USD), a motor (1.2USD), a sample cell (0.2 USD) and an SPCE connector (0.5 USD). The potentiostat was connected to the SPCE connector by dupont wire.\u003c/p\u003e \u003cp\u003eThe stripping curves using self-made PSoC Stat potentiostat were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea. With the increase of Cd\u003csup\u003e2+\u003c/sup\u003e concentration, the stripping peak potential shifted towards positive potential direction, and the stripping peak current enhanced. The peak current showed a good linear relationship with Cd\u003csup\u003e2+\u003c/sup\u003e concentration in the range of 5\u0026thinsp;~\u0026thinsp;100 \u0026micro;g/L (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). The linear regression equation was Ip\u0026thinsp;=\u0026thinsp;0.29C\u0026thinsp;+\u0026thinsp;0.35, and the lowest detection limit of Cd\u003csup\u003e2+\u003c/sup\u003e was 3.55 \u0026micro;g/L (S/N\u0026thinsp;=\u0026thinsp;3). The stripping curves using commercial potentiostat were shown in Fig. S5a. The limit of detection reached 0.15 \u0026micro;g/L, and the linear range was 1\u0026thinsp;~\u0026thinsp;100 \u0026micro;g/L (Fig. S5b). Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows some reported electrochemical methods for Cd\u003csup\u003e2+\u003c/sup\u003e determination. It can be seen that compared with other methods, our proposed method demonstrates competitive sensitivity and linear range. More importantly, our method holds great advantage in the point-of-care testing (POCT). Although the limit of detection using self-made PSoC Stat potentiostat is higher than that using commercial potentiostat, it was lower than the maximum permissible level of Cd in drinking water (5 \u0026micro;g/L) \u003csup\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e, which is sufficient for the on-site determination of Cd\u003csup\u003e2+\u003c/sup\u003e. In addition, the Bi/Pre-anodized SPCE can simultaneously determine Cd\u003csup\u003e2+\u003c/sup\u003e and Pb\u003csup\u003e2+\u003c/sup\u003e (Fig. S6), demonstrating the ability of multiple detection.\u003c/p\u003e \u003cp\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\u003eComparison of different electrochemical sensors for Cd\u003csup\u003e2+\u003c/sup\u003e determination\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=\"left\" 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=\"left\" 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\u003eElectrode type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eElectrode modification\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLinear range\u003c/p\u003e \u003cp\u003e(\u0026micro;g/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLOD (\u0026micro;g/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eInstrument\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRef.\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCarbon\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBOC\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10\u0026thinsp;~\u0026thinsp;50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ecommercial\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[30]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eScreen-printed gold electrode\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNafion-Bi\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50\u0026thinsp;~\u0026thinsp;300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ecommercial\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[31]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCarbon\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAgNP/Graphene/Nafion\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e25\u0026thinsp;~\u0026thinsp;250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ecommercial\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[32]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSPCE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBismuth film\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.5\u0026thinsp;~\u0026thinsp;72.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ecommercial\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[33]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSPCE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003erGO/SMOF/PEI\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e56.3\u0026thinsp;~\u0026thinsp;1406.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e33.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePOCT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[34]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGC-SPE\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBismuth film\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.5\u0026thinsp;~\u0026thinsp;200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ecommercial\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[35]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNC-BBD\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBismuth film\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u0026thinsp;~\u0026thinsp;280\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ecommercial\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[36]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSPCE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBi PASPCE (+\u0026thinsp;NaBr)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u0026thinsp;~\u0026thinsp;100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ecommercial\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eThis work\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSPCE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBi PASPCE (+\u0026thinsp;NaBr)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5\u0026thinsp;~\u0026thinsp;100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePOCT\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 \u003cp\u003e \u003csup\u003e1\u003c/sup\u003eBOC: Bismuth oxycarbide/nafion; \u003csup\u003e2\u003c/sup\u003eNafion-Bi: in situ modification of bismuth and nafion; \u003csup\u003e3\u003c/sup\u003eAgNP: silver nanoparticles; \u003csup\u003e4\u003c/sup\u003erGO/SMOF/PEI: graphene oxide /SMOF (composited by single wall carbon nanotube and UiO-66-NH\u003csub\u003e2\u003c/sub\u003e MOF) /polyethyleneimine; \u003csup\u003e5\u003c/sup\u003eGC-SPE: glassy carbon microparticle stencil printed electrode; \u003csup\u003e6\u003c/sup\u003eNC-BBD: nitrogen rich porous carbon/boron doped diamond composite electrode.\u003c/p\u003e \u003cp\u003eThe repeatability of the proposed electrode for Cd\u003csup\u003e2+\u003c/sup\u003e determination was evaluated by 10 consecutive tests of 50 \u0026micro;g/L Cd\u003csup\u003e2+\u003c/sup\u003e standard solution (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). The relative standard deviation (RSD) of the measured peak current values was 4.4%, which indicates a good repeatability. Moreover, considering the interference from other potential metal ions in the determination of Cd\u003csup\u003e2+\u003c/sup\u003e in actual samples, the anti-interference ability of Bi/Pre-anodized SPCE was studied. Ca\u003csup\u003e2+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Hg\u003csup\u003e2+\u003c/sup\u003e, Fe\u003csup\u003e3+\u003c/sup\u003e and K\u003csup\u003e+\u003c/sup\u003e with a concentration 10 times higher than that of Cd\u003csup\u003e2+\u003c/sup\u003e, as well as a similar concentration of Pb\u003csup\u003e2+\u003c/sup\u003e and Cu\u003csup\u003e2+\u003c/sup\u003e was added to the supporting electrolyte containing 50 \u0026micro;g/L Cd\u003csup\u003e2+\u003c/sup\u003e as interfering ion, respectively. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed, Ca\u003csup\u003e2+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Fe\u003csup\u003e3+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e and Pb\u003csup\u003e2+\u003c/sup\u003e had little interference on the determination of Cd\u003csup\u003e2+\u003c/sup\u003e, while Cu\u003csup\u003e2+\u003c/sup\u003e significantly reduced the stripping peak current of Cd\u003csup\u003e2+\u003c/sup\u003e. This inhibition may be due to the competition between Bi\u003csup\u003e3+\u003c/sup\u003e and Cu\u003csup\u003e2+\u003c/sup\u003e for the active site on the working electrode during deposition as well as the formation of intermetallic compounds among copper and cadmium\u003csup\u003e[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e. The interference from Cu\u003csup\u003e2+\u003c/sup\u003e can be eliminated by the addition of 40 \u0026micro;mol/L potassium ferrocyanide into the detection solution (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Recovery studies\u003c/h2\u003e \u003cp\u003eTo assess the feasibility of the developed heavy metal electrochemical sensor in practical applications, a spike-recovery method was used to detect Cd\u003csup\u003e2+\u003c/sup\u003e in tap water and rice extract. The pre-treatment of tap water and rice samples were described in 2.4. The spiked amount of Cd\u003csup\u003e2+\u003c/sup\u003e were set to four different levels. Each spiked sample was measured three times in parallel. Simultaneously, the spiked samples were determined by ICP-MS.\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\u003eResults of Cd\u003csup\u003e2+\u003c/sup\u003e determination in tap water and rice samples using PSoC Stat potentiostat\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\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=\"left\" 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=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpiked\u003c/p\u003e \u003cp\u003e(\u0026micro;g/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFound\u003c/p\u003e \u003cp\u003e(\u0026micro;g/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRecovery rate (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRSD* (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eFound by ICP-MS\u003c/p\u003e \u003cp\u003e(\u0026micro;g/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e|Error|\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003cp\u003e10.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e107.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003cp\u003e3.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003cp\u003e10.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003cp\u003e3.9%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTap water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e91.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e29.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e6.4%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e57.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e95.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e60.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e6.1%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003cp\u003e9.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003cp\u003e92.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003cp\u003e3.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003cp\u003e9.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003cp\u003e6.1%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRice\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e103.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e32.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.0%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e61.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e103.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e63.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.7%\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\u003e* Relative standard deviation. For each concentration, three replicates were measured.\u003c/p\u003e \u003cp\u003eAs shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, when using our proposed electrochemical sensor, the recoveries in water and rice samples ranged from 91.7\u0026ndash;107.1%, and the RSD were between 2.09% and 5.26%. In addition, the detection results were consistent with ICP-MS with deviation below 10%. These results demonstrate that the heavy metal electrochemical sensor owns great accuracy and reliability, and can be applied to the determination of Cd\u003csup\u003e2+\u003c/sup\u003e in tap water and rice samples.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eA metal-bismuth modified pre-anodized screen-printed electrode was prepared based on the pre-anodization and in-situ deposition technique. Various electrochemical characteristics proved the successful preparation of the modified electrode. Benefiting from pre-anodization, bismuth co-deposition and bromine sensitization, the electron transfer ability was improved, the enrichment of Cd\u003csup\u003e2+\u003c/sup\u003e was facilitated, and the sensitivity of the electrode for Cd\u003csup\u003e2+\u003c/sup\u003e determination was significantly enhanced. Coupled with the self-made, portable and low-cost potentiostat and stirring device, the electrochemical sensor has a wide linear range of 5 ~ 100 µg/L and a low detection limit of 3.55 µg/L, possesses good repeatability and specificity. In addition, it can be applied to the determination of Cd\u003csup\u003e2+\u003c/sup\u003e in drinking water and rice. Our work provides a promising electrode fabrication method and a point of need device for electrochemical determination of heavy metals."},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCRediT authorship Contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eYongfang Li:\u003c/strong\u003e Conceptualization, Methodology, Formal analysis, Data curation, Writing-original draft, Funding acquisition;\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eZijun Wang:\u003c/strong\u003e Methodology, Investigation, Data curation, Writing-review and editing;\u003cstrong\u003e\u0026nbsp;Xuan Chen:\u003c/strong\u003e Methodology,\u0026nbsp;Validation, Data curation, Writing-review and editing;\u003cstrong\u003e\u0026nbsp;Zhijian Yi:\u003c/strong\u003e Methodology, Software, Data curation, Writing-review and editing; \u003cstrong\u003eRui Wang:\u003c/strong\u003e Validation, Resources, Writing-review and editing, Visualization, Supervision, Project administration, Funding acquisition.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of Competing Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgment\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was funded by start-up funds for scientific research of high-level talents in Foshan University and the National Natural Science Foundation of China (32371521).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eFatima, G., Raza, A. 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Eng\u003c/em\u003e\u003cem\u003e.\u003c/em\u003e\u003cstrong\u003e11\u003c/strong\u003e (2023).\u003c/li\u003e\n\u003cli\u003eSaeed, A. A., Singh, B., Abbas, M. N., Dempsey, E. Evaluation of bismuth modified carbon thread electrode for simultaneous and highly sensitive Cd (II) and Pb (II) determination. \u003cem\u003eElectroanal.\u003c/em\u003e\u003cstrong\u003e28,\u003c/strong\u003e 2205-2213(2016).\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":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"pre-anodization, bismuth modification, electrochemical sensor, Cd2+, portable device","lastPublishedDoi":"10.21203/rs.3.rs-4600103/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4600103/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eElectrochemical detection is favorable for the rapid and sensitive determination of heavy metal cadmium. However, the detection sensitivity needs to be further improved, and a portable, low-cost device is needed for on-site detection. Herein, an in-situ bismuth modified pre-anodized screen-printed carbon electrode (SPCE) was developed for Cd\u003csup\u003e2+\u003c/sup\u003e determination by square wave anodic stripping voltammetry (SWASV). The in-situ bismuth modification enhances the enrichment of Cd\u003csup\u003e2+\u003c/sup\u003e, and together with pre-anodization improve the electron transfer rate of electrode, thus enhancing the detection sensitivity. In addition, a self-made PSoC Stat potentiostat coupled with a stirring device was fabricated for portable electrochemical detection. After comprehensive optimization, the developed method can reach a testing time of 3 min, a detection limit of 3.55 \u0026micro;g/L, a linear range of 5-100 \u0026micro;g/L, and a recovery rate of 91.7%-107.1% in water and rice samples for Cd\u003csup\u003e2+\u003c/sup\u003e determination. Therefore, our method holds great promise for the rapid, sensitive and on-site determination of Cd\u003csup\u003e2+\u003c/sup\u003e in food samples.\u003c/p\u003e","manuscriptTitle":"In situ deposition of bismuth on pre-anodized screen-printed electrode for sensitive determination of Cd2+ in water and rice with a portable device","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-08 08:06:18","doi":"10.21203/rs.3.rs-4600103/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-07-09T12:23:58+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-05T11:43:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"339240407645935390051261705289917190668","date":"2024-06-25T07:45:26+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-25T07:24:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"270638502237999531750160659844775595497","date":"2024-06-25T06:15:49+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-06-24T17:22:33+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-06-24T17:17:07+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-06-21T16:41:37+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-06-19T13:15:10+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-06-18T12:49:23+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"82e15d6f-d6b3-48cf-8b55-8801e8a95455","owner":[],"postedDate":"July 8th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-08-12T15:59:30+00:00","versionOfRecord":{"articleIdentity":"rs-4600103","link":"https://doi.org/10.1038/s41598-024-69626-7","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2024-08-08 15:57:02","publishedOnDateReadable":"August 8th, 2024"},"versionCreatedAt":"2024-07-08 08:06:18","video":"","vorDoi":"10.1038/s41598-024-69626-7","vorDoiUrl":"https://doi.org/10.1038/s41598-024-69626-7","workflowStages":[]},"version":"v1","identity":"rs-4600103","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4600103","identity":"rs-4600103","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}