A WSe2@poly(3,4-ethylenedioxythiophene) nanocomposite-based electrochemical sensor for simultaneous detection of dopamine and uric acid: http://dx.doi.org/10.5599/jese.1375 1251 J. Electrochem. Sci. Eng. 12(6) (2022) 1251-1259; http://dx.doi.org/10.5599/jese.1375 Open Access : : ISSN 1847-9286 www.jESE-online.org Original scientific paper A WSe2@poly(3,4-ethylenedioxythiophene) nanocomposite- based electrochemical sensor for simultaneous detection of dopamine and uric acid Yasin Tangal1, Deniz Coban2 and Sadik Cogal3, 1Burdur Mehmet Akif Ersoy University, The Graduate School of Natural and Applied Sciences, Department of Chemistry, 15030, Burdur, Turkey 2Burdur Mehmet Akif Ersoy University, The Graduate School of Natural and Applied Sciences, Department of Material Technology Engineering, 15030, Burdur, Turkey 3Burdur Mehmet Akif Ersoy University, Faculty of Arts and Science, Department of Chemistry, 15030, Burdur, Turkey Corresponding author: sadik_cogal@yahoo.com; Tel.: +90-248-213-3060; Fax: +90-248-213-3099 Received: May 13, 2022; Accepted: June 24, 2022; Published: July 25, 2022 Abstract In the present work, a nanocomposite of two-dimensional WSe2 nanosheets with poly- (3,4-ethylenedioxythiophene (WSe2@PEDOT) was prepared by facile hydrothermal method and characterized in terms of structural and morphological analyses. This nanocomposite was used to modify glassy carbon electrode for the construction of an electrochemical sensing platform for simultaneous determination of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA). It was found that the incorporation of PEDOT into WSe2 nanosheets exhibited enhanced electrochemical behaviors and electro¬catalytic activity against DA and UA. Using differential pulse voltammetry (DPV) measurements, the WSe2@PEDOT modified electrode displayed wide linear detection ranges of 16 to 466 µM for DA and 20 to 582.5 µM for UA. The electrode also exhibited high selectivity against DA and UA in the presence of major interference of ascorbic acid and other interferent substances. Keywords Tungsten diselenide; conducting polymer; modified electrode; selective sensing; biological compounds Introduction Dopamine (DA) and uric acid (UA) are two important biological compounds that play important roles in human physiological functions [1]. Abnormal concentrations of these molecules in biological fluids lead to many diseases, including schizophrenia, Alzheimer, Parkinson’s disease, drug addiction, hyperuricemia, chronic renal sickness, etc. [2-4]. Therefore, early analyses of these molecules are highly important to deal with the concerned conditions. Recently, electrochemical methods have http://dx.doi.org/10.5599/jese.1375 http://dx.doi.org/10.5599/jese.1375 http://www.jese-online.org/ mailto:sadik_cogal@yahoo.com J. Electrochem. Sci. Eng. 12(6) (2022) 1251-1259 WSe2@PEDOT NANOCOMPOSITE BASED SENSOR 1252 become attractive for the determination of DA and UA [5,6]. However, these two electroactive molecules have close oxidation potentials, which limits their selective detection in biological samples on traditional electrodes. Therefore, tremendous research efforts have been directed toward the development of novel electrodes based on various materials. Among these, two-dimensional (2D) nanomaterials such as graphene and its inorganic analogues have attracted significant interest in electrochemical applications because of their unique chemical and physical properties [7]. For example, transition metal dichalcogenides (TMDs) have been widely investigated as electrode materials for electrochemical sensing platforms due to their high electrocatalytic properties, chemical stability, low cost and facile synthesis [8-10]. WSe2, an important member of TMDs, has received special attention in electrochemical applications [11,12]. However, WSe2 tends to stack easily due to high interactions between its layers, which decrease the number of electroactive sites and electro- chemical performance. Therefore, various strategies have been applied to improve the electroche- mical performance to decrease the number of layers and enhance the number of active sites. Among the alternative strategies, the production of WSe2 in the presence of conductive supports is an effective way to reduce the number of layers by preventing layer stacking. Conducting polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) can be incorporated with TMD materials to prepare composite electrode materials [13,14]. PEDOT possesses high conductivity and electrochemical stability and shows high potential to be applied to an electrode material [15]. PEDOT- like supporting materials not only prevent the stacking of WSe2 layers but also increase the active sites of WSe2. In this work, WSe2@PEDOT composite was prepared via a hydrothermal method to enhance the electrochemical properties of WSe2. The as-prepared composite was coated on a glassy carbon electrode (GCE) for electrochemical detection of DA and UA. Experimental Materials: Tungstic acid (H2WO4) (Aldrich, 99 %), selenium (Se) powder (Sigma-Aldrich, 99.0 %), sodium borohydride (NaBH4) (Sigma-Aldrich, ≥98 %), 3,4-ethylenedioxythiophene (EDOT) (Sigma- Aldrich, 97 %), iron (III) chloride (FeCl3) (Carlo Erba), potassium chloride (Sigma-Aldrich), potassium ferricyanide(III) (K3Fe(CN)6) (Sigma-Aldrich, 99 %), potassium hexacyanoferrate(II) trihydrate (K4[Fe(CN)6]∙3H2O) (Merck), sodium phosphate monobasic dihydrate (NaH2PO4∙2H2O) (Sigma- Aldrich), sodium phosphate dibasic dihydrate (Na2HPO4∙2H2O) (Sigma-Aldrich) and dimethyl- formamide (DMF) (Merck) were purchased and used as received. Synthesis of PEDOT: PEDOT was synthesized via the oxidative chemical polymerization method. 100 µL of monomer EDOT was dissolved in 50 mL deionized water (DIW) and placed in an ice bath. In another flask, 422.9 mg ammonium persulfate (APS) (EDOT:APS molar ratio is 1:2) was dissolved in 25 mL DIW and then transferred slowly to monomer solution, keeping the temperature of the solution between 0-5 °C. The reaction mixture was stirred for 48 h at room temperature. The obtained black powder was filtered, washed with DIW and ethanol several times and finally dried at 60 °C for 24 h. Synthesis of WSe2@PEDOT The preparation of WSe2@PEDOT was carried out as follows: first, 0.1 g of as-prepared PEDOT was ultrasonically dispersed in 30 mL of DMF for 60 min. Then, 0.32 g Se powder and 0.1 g NaBH4 as a reducing agent were added and stirred for 60 min to obtain good dispersion. Later, 0.49 g H2WO4 was slowly added to this dispersion and stirred for an additional 30 min. The final dispersion was transferred to a 45 mL Teflon-lined stainless steel autoclave reactor and heated at 200 °C for 12 h. After being cooled to room temperature, the product was filtered and washed with DW at Y. Tangal et al. J. Electrochem. Sci. Eng. 12(6) (2022) 1251-1259 http://dx.doi.org/10.5599/jese.1375 1253 least three times and finally dried at 60 °C. The obtained powder was annealed at 500 °C for 3 h under N2 flow to enhance the crystallinity. The synthesis of WSe2 as control was the same as that of WSe2@PEDOT, except PEDOT was not added to the reaction mixture. Electrode modification Before coating, the cleaning process was applied to polish the GCE surface by using 0.3 and 0.05 µm alumina powder. GCE was then sonicated in DW and ethanol to remove any adsorbed particles on its surface. On the other hand, well-dispersed electrode ink was prepared by sonication of WSe2@PEDOT in DMF for 1 h to obtain a concentration of 5 mg mL-1 WSe2@PEDOT. Later, 10 μL from this ink was drop-coated on GCE and left to dry in an open atmosphere. Finally, WSe2@PEDOT coated-GCE was carefully rinsed with 0.1 M phosphate buffer solution (PBS) before experiments. For the control, GCE was also modified with pristine WSe2 in the same way described above for GCE/WSe2@PEDOT. Electrochemical measurements Electrochemical experiments were conducted via Ivium CompactStat model potentiostat. Three- electrode configuration was used for electrochemical works, and in addition to GCE as a working electrode, Pt wire was used as a counter electrode and Ag/AgCl as a reference electrode. Characterization The crystal structure of the as-prepared WSe2@PEDOT was determined through X-ray diffraction (XRD) using Bruker/D8 Advance diffractometer. Morphological characterization was conducted using scanning electron microscopy (FEI Model: Quanta 400F) and transmission electron microscopy (FEI Tecnai G2 Spirit Biotwin model). Figure 1. Schematic representation of synthetic procedure and electrochemical detection Results and discussion Materials characterization WSe2@PEDOT composite was successfully obtained via hydrothermal reaction, as schematically represented in Figure 1. In this synthesis procedure, metallic Se particles were initially reduced by a http://dx.doi.org/10.5599/jese.1375 J. Electrochem. Sci. Eng. 12(6) (2022) 1251-1259 WSe2@PEDOT NANOCOMPOSITE BASED SENSOR 1254 reducing agent of NaBH4 to produce Se2- ions. The Se2- ions were then reacted with W cations, forming WSe2 nanosheets embedded in PEDOT polymeric structure. The structure of the WSe2@PEDOT composite was evaluated by X-ray diffraction (XRD). Figure 2 shows the XRD patterns of the WSe2@PEDOT composite as well as pristine WSe2 nanosheets. XRD pattern of WSe2 displays major diffraction peaks (planes) at 13.3o (002), 31.9o (100), 37.6o (103), 47.3o (105), 55.9o (110), 65.8o (108) and 70.3o (203), which are in good agreement with the well- known hexagonal WSe2 structure (JCPDS No. 38-1388) [16]. On the other hand, the WSe2@PEDOT composite exhibited diffraction peaks at 13.2, 23.0, 31.4, 32.8, 37.8, 40.6, 47.3, 53.3, 55.9, 65.7, 69.4 and 74.2°, in which the major diffraction peaks of WSe2 hexagonal structure are well matched. Moreover, the major diffraction peaks are relatively stronger, and additional diffraction peaks are also observed in the WSe2@PEDOT composite, suggesting the successful combination of WSe2 nanosheets and conducting polymer. 2 / o Figure 2. XRD pattern of WSe2 nanosheets and WSe2@PEDOT composite The surface morphology of the WSe2@PEDOT composite was investigated using SEM and TEM. The SEM images (Figure 3a-b) of pristine WSe2 and WSe2@PEDOT indicate that nanosheets incorporated flower-like structures were obtained by hydrothermal treatment. However, the WSe2@PEDOT possesses looser, dispersed and thinner nanosheets due to the incorporation of PEDOT. This difference is more obvious in the TEM images, as shown in Figure 3c-d. Thus, the resulting composite can have more active sites for analyte adsorption, leading to an improved electrochemical signal. 2 / o Figure 3. (a,b) SEM and (c,d) TEM images of WSe2 (left) and WSe2@PEDOT (right) Y. Tangal et al. J. Electrochem. Sci. Eng. 12(6) (2022) 1251-1259 http://dx.doi.org/10.5599/jese.1375 1255 Electrochemical studies To assess the electrochemical behavior, modified electrodes were investigated via cyclic voltammetry (CV) in 0.1 M KCl containing 5 mM [Fe(CN)6]3-/4-, conducted between -0.3 to 0.6 V at 50 mV s-1 of scan rate (). Figure 4(a) shows CVs of bare GCE, GCE-WSe2 and GCE-WSe2@PEDOT in this solution. It is obvious that the WSe2@PEDOT composite-modified electrode exhibited better electrochemical kinetics against ferri/ferrocyanide couple than bare GCE and GCE-WSe2. WSe2@PEDOT displays 99.1 / -106.1 µA of anodic/cathodic peak currents, while the bare GCE and GCE-WSe2 show 51.2 / -60.1 µA and 75.01 / -86.3 µA, respectively. The enhanced electrochemical kinetics of GCE-WSe2@PEDOT could be attributed to the enhanced number of electroactive sites and higher conductivity due to the incorporation of conductive PEDOT in WSe2 nanosheets. To estimate the electrochemically active surface area of the GCE-WSe2@PEDOT electrode, CV measurements at various scan rates were performed in 0.1 M KCl containing 5 mM [Fe(CN)6]3-/4- (Figure 4b). The inset figure shows that the anodic peak currents increased linearly with the square root of scan rates (1/2). Therefore, the electrochemically active surface area (A / cm2) was calculated using Randles-Ševčik equation (1) [17]: Ipa = (2.65 x 105) n3/2AD1/2C1/2 (1) where D is the diffusion coefficient, which is 7.610-6 cm2 s-1 for [Fe(CN)6]3-/4-. The electrochemical surface area of the GCE-WSe2@PEDOT electrode was estimated to be 0.13 cm2, which is higher than 0.063 cm2 estimated for bare GCE. In order to determine the electrocatalytic activities of bare, WSe2 and WSe2@PEDOT modified electrodes toward a binary mixture of DA and UA, the CV and DPV measurements were performed in 0.1 M PBS solution containing 0.19 mM DA and 0.28 mM UA. Figure 4c shows CVs of different electrodes performed in the potential range between -0.2 to +0.6 V, at 50 mV/s of scan rate. It is clearly seen that the current response of bare GCE is very low, which does not provide a sensitive sensing system for the determination of DA and UA. On the other hand, as it is expected by modifying the GCE electrode, the current response was improved and the highest activity was obtained with the electrode modified with WSe2@PEDOT composite. Electrocatalytic activities of electrodes were further investigated using the DPV technique, which is known as a more sensitive electrochemical method. Figure 4d shows that oxidation peak positions and their current responses are more obvious than was observed in CV measurements. Therefore, the DPV technique was chosen for the simultaneous determination of DA and UA. Moreover, from the CV and DPV curves, it is obviously seen that the current response of UA was greatly increased. This enhancement of the WSe2@PEDOT modified electrode toward UA is due to the presence of PEDOT conducting polymer. At the working pH, DA has a cationic character and UA exists as an anionic form, which leads to enhanced electrostatic interaction between UA and cationic PEDOT [18]. Therefore, different interactions of DA and UA with the WSe2@PEDOT composite result in peak separation of DA and UA. Cyclic voltammetry was also used to evaluate the effect of various scan rates on the electrocatalytic behaviors of DA and UA on the WSe2@PEDOT electrode and to understand the reaction kinetics on its surface. Figure 5(a) displays CVs of DA (0.28 mM) and UA (0.37 mM) in 0.1 M PBS at varied scan rates from 25 to 250 mV/s. Figure 5b shows the corresponding oxidation peak currents, which are proportional to the scan rate, indicating an adsorption-controlled process on WSe2@PEDOT coated electrode [19]. http://dx.doi.org/10.5599/jese.1375 J. Electrochem. Sci. Eng. 12(6) (2022) 1251-1259 WSe2@PEDOT NANOCOMPOSITE BASED SENSOR 1256 Figure 4. (a) CVs of GCE, GCE-WSe2 and GCE-WSe2@PEDOT in 0.1 M KCl containing 5 mM [Fe(CN)6] 3-/4-; (b) CVs of GCE-WSe2@PEDOT in 0.1 M KCl containing 5 mM [Fe(CN)6] 3-/4- at different scan rates; Inset figure shows anodic peak currents vs. square roots of scan rates; (c) CVs of GCE, GCE-WSe2 and GCE-WSe2@PEDOT in 0.1 M PBS solution containing 0.19 mM DA and 0.28 mM UA; (d) DPVs of GCE-WSe2 and GCE- WSe2@PEDOT in 0.1 M PBS solution containing 0.19 mM DA and 0.28 mM UA Figure 5. (a) CVs of GCE-WSe2@PEDOT in 0.1 M PBS (pH 7.0) containing 1.5 mM AA, 0.36 mM DA and 0.55 mM UA at different scan rates from 25-25 mV/s; (b) linear plots of anodic peak currents of DA and UA vs. scan rate The simultaneous determination of DA and UA on GCE-WSe2@PEDOT was performed using DPV. Figure 6a displays the DPVs for increasing DA and UA concentrations in 0.1 M PBS. It is obvious that oxidation peak positions of DA and UA maintain the peak-to-peak potential separation by gradually increasing their concentrations. Figure 6(b-c) displays calibration curves of DA and UA and linear detection ranges of 16 to 466 µM for DA and 20 to 582.5 µM for UA, were determined. The linear regression equations with corresponding regression coefficients were also placed in Figure 6b, c. Furthermore, considering the slopes of the regression equations, LODs were evaluated to be 8 µM for DA and 14 µM UA, respectively. Y. Tangal et al. J. Electrochem. Sci. Eng. 12(6) (2022) 1251-1259 http://dx.doi.org/10.5599/jese.1375 1257 Figure 6. (a) DPVs of GCE-WSe2@PEDOT in 0.1 M PBS (pH 7.0) containing various concentrations of DA and UA; calibration plots of (b) DA and (c) UA Selectivity, reproducibility and stability of the sensor The selectivity of the GCE-WSe2@PEDOT electrode was investigated through DPV technique. The major interference molecule is ascorbic acid, found in a much higher concentration than DA and UA in biological fluids. Figure 7a shows DPVs of GCE-WSe2@PEDOT in 0.1 M PBS solution containing 0.38 mM DA, 0.38 mM UA and 1.0 mM AA and other interference substances (e.g., NaCl, KCl, NaNO3, MgSO4, glucose and citric acid). Figure 7. (a) DPVs of GCE-WSe2@PEDOT in 0.1 M PBS (pH 6.0) containing 1.0 mM interfering substances in presence of 0.38 mM DA and 0.38 mM UA; (b) stability test It is clearly seen that adding interfering substances in much higher concentrations to the mixed DA and UA solution does not have an obvious change in their peak currents, indicating high selectivity of http://dx.doi.org/10.5599/jese.1375 J. Electrochem. Sci. Eng. 12(6) (2022) 1251-1259 WSe2@PEDOT NANOCOMPOSITE BASED SENSOR 1258 the sensor. It is also worth noting that the electrode modified with WSe2@PEDOT inhibits the oxidation of AA, which has a close oxidation potential to DA and UA. The stability test of the GCE- WSe2@PEDOT electrode was also investigated using the DPV technique. The stability data was collected by obtaining the peak current values of DA and UA for fifteen days and given in Figure 7b, indicating an acceptable change compared with the initial currents. Conclusions WSe2@PEDOT composite was successfully prepared via a simple hydrothermal method and applied as an electrochemical sensor for the detection of DA and UA. It was found that the incorporation of conducting PEDOT polymer into the WSe2 nanostructure improved electrochemical behavior and electrocatalytic activity of composite material. Furthermore, WSe2@PEDOT modified electrode gave separated oxidation peaks for DA and UA with better current responses. WSe2@PEDOT-based sensor exhibited a linear detection range of 16 to 466 µM for DA and 20 to 582.5 µM for UA and detection limits of 8 µM for DA and 14 µM UA, respectively. 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This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license (https://creativecommons.org/licenses/by/4.0/) http://dx.doi.org/10.5599/jese.1375 https://doi.org/10.1016/j.aca.2018.02.080 https://doi.org/10.1021/acsanm.1c00594 https://doi.org/10.1016/j.microc.2022.107188 https://doi.org/10.1007/s00216-020-02455-5 https://doi.org/10.1039/C4RA04046E https://creativecommons.org/licenses/by/4.0/) @Article{Tangal2022, author = {Tangal, Yasin and Coban, Deniz and Cogal, Sadik}, journal = {Journal of Electrochemical Science and Engineering}, title = {{A WSe2@poly(3,4-ethylenedioxythiophene) nanocomposite-based electrochemical sensor for simultaneous detection of dopamine and uric acid:}}, year = {2022}, issn = {1847-9286}, month = {jul}, number = {6}, pages = {1251--1259}, volume = {12}, abstract = {In the present work, a nanocomposite of two-dimensional WSe2 nanosheets with poly-(3,4‑ethylenedioxythiophene (WSe2@PEDOT) was prepared by facile hydrothermal method and characterized in terms of structural and morphological analyses. This nano­composite was used to modify glassy carbon electrode for the construction of an electrochemical sen­sing platform for simultaneous determination of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA). It was found that the incorporation of PEDOT into WSe2 nano­sheets exhibited enhanced electrochemical behaviors and electro¬catalytic activity against DA and UA. Using differential pulse voltammetry (DPV) measurements, the WSe2@PEDOT modified electrode displayed wide linear detection ranges of 16 to 466 µM for DA and 20 to 582.5 µM for UA. The electrode also exhibited high selectivity against DA and UA in the presence of major interference of ascorbic acid and other interferent substances.}, doi = {10.5599/JESE.1375}, file = {:D\:/OneDrive/Mendeley Desktop/Tangal, Coban, Cogal - 2022 - A WSe2@poly(3,4-ethylenedioxythiophene) nanocomposite-based electrochemical sensor for simultaneous detect.pdf:pdf;:17_jESE_1375_1251-1259.docx:Word_NEW;:17_jESE_1375_1251-1259.docx:Word_NEW;:www/jESE_V12_No6_1251-1259.pdf:PDF}, keywords = {Tungsten diselenide, biological compounds, conducting polymer, modified electrode, selective sensing}, publisher = {International Association of Physical Chemists (IAPC)}, url = {https://pub.iapchem.org/ojs/index.php/JESE/article/view/1375}, }