Electrodeposited conducting polymer PEDOT doped with pure carbon nanotubes for the detection of dopamine in the presence of ascorbic acid
Introduction
As one of the most important neurotransmitters, dopamine (DA) plays an essential role in the cardiovascular, renal, hormonal, and central nervous systems. Alterations in DA contribute to the development of a number of severe mental illnesses, such as Huntington's disease, schizophrenia, Parkinson's disease, and depression [1], [2], [3]. DA is also used to increase the splanchnic blood flow and splanchnic oxygen uptake in patients with septic shock [4] and as a therapeutic drug to reduce the risk of renal failure by increasing renal blood flow [5], [6]. Therefore, there is a great interest in the development of reliable dopamine assays with good sensitivity and selectivity. Fluorescence [7], spectrophotometry [8], [9] and chromatography [10], [11], [12], [13] are the most frequently applied assay methods. However, these methods suffer from certain disadvantages such as high costs, long analysis time, and, in some cases, poor selectivity and low sensitivity. In recent years, different methods based on electrochemical techniques have been developed for the determination of DA, as it can be easily electrochemically oxidized [14]. Various strategies have been used to prepare chemically modified electrodes with different materials for the electroanalysis of DA [15], [16], [17], [18].
The basic mechanism of most electrochemical DA sensors is mediated by the redox activity of DA. However, DA determination using electrochemical approaches is limited by interferences from other electroactive substances, such as ascorbic acid (AA), which coexists with DA in physiological samples. For example, both DA and AA are present in the human brain, where the concentration of AA is about 1000 times higher than that of DA [19]. Because the redox potentials of DA and AA at many electrode substrates are very close to each other or even overlap, it is difficult to differentiate their electrochemical responses. To address the DA selectivity problems, two main categories of electrode modifications have been developed. One is the application of an anti-interference layer to prevent the AA or other interfering compounds from reaching the electrode surface [18]. The other is the addition of materials that can electrocatalytically oxidize/reduce the reduced/oxidized forms of DA and AA at different potentials.
In the past years, different materials such as polypyrrole doped with sulfonated β-cyclodextrins [14], self-assembled peptide [15], carbon nanotubes (CNTs) [16], polypyrrole derivatives [17], graphene [19], choline and acetylcholine [20], p-Phenylenediamine [21], self-assembled monolayer of corrole and other thiol derivatives [22], electropolymerized sulfobutylether cyclodextrin-doped with poly(N-acetyltyramine) and polypyrrole [23] have been used to detect DA. As both conducting polymers [14], [17], [23] and CNTs [16], [24], [25], [26] have exhibited excellent catalytic properties, in this work, we prepared a biocompatible nanocomposite [27] composed of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and CNTs for the electrocatalytic detection of DA. PEDOT doped with pure CNTs was electrodeposited on the surface of a carbon paste electrode (CPE), and the PEDOT/CNT modified CPE showed good catalytic effects on the electrochemical redox reaction of DA. Due to the excellent stability of the PEDOT/CNT nanocomposite and its catalytic property toward DA, a highly stable and sensitive DA sensor was developed that performs favorably in the presence of a high concentration of the common interferent AA.
Section snippets
Materials and apparatus
DA and AA were purchased from Aladdin Industry Corporation (Shanghai, China). 3,4-Ethylenedioxythiophene (EDOT) and poly(styrene sulfonic acid) (PSS) were purchased from Sigma–Aldrich. Multi-walled CNTs with the diameter of 10–20 nm and length of 10–30 μm were purchased from Cheap Tubes Inc. (Brattleboro, USA). Solutions with different pHs were obtained by adjusting 0.2 M Britton–Robinson (B-R) mother solution with 0.2 M NaOH (Carlo Erba). The stock solution of 0.5 mmol L−1 DA was prepared in 0.2 M
Electrochemical behavior of DA
Fig. 1 shows the typical CVs of DA obtained at the bare CPE (curve a), the CNT/CPE (curve b), the PEDOT/PSS/CPE (curve c) and the PEDOT/CNT/CPE (curve d), respectively. As can be seen, the peak-potential separation between the Epa and the Epc (ΔEp) at the PEDOT/CNT/CPE (77 mV) is much smaller than that at the bare CPE (358 mV), the CNT/CPE (128 mV), and the PEDOT/PSS/CPE (120 mV). The greatly enhanced peak current and reduced peak separation are strong indicatives of the catalytic properties of the
Conclusions
A sensitive and selective electrochemical sensor for the detection of DA was developed based on the modification of a CPE with a conducting polymer nanocomposite PEDOT/CNT, which was prepared through the electrochemical polymerization of EDOT in the presence of only CNTs. The PEDOT/CNT modified electrode showed excellent catalytic properties toward the electrochemical reaction of DA, and it was not affected in the presence of AA. In addition, the DA sensor exhibited satisfying long-term
Acknowledgements
This research was supported by the National Natural Science Foundation of China (No. 21275087), the Natural Science Foundation of Shandong Province of China (ZR2012BM008), and the Taishan Scholar Program of Shandong Province, China. X.T.C. acknowledges the support of the National Science Foundation Grant 0748001.
Ms. Beibei Li is currently a postgraduate student of the College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology. Her research interest is focused on the preparation and application of electrochemical sensors and biosensors.
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Cited by (0)
Ms. Beibei Li is currently a postgraduate student of the College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology. Her research interest is focused on the preparation and application of electrochemical sensors and biosensors.
Mr. Luyang Ling is currently an undergraduate student of the College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology. His research interest is focused on the preparation and application of electrochemical sensors and biosensors.
Dr. Guiyun Xu is currently an associate professor of the College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology. Dr Xu obtained her Ph.D. from Ocean University of China in 2007. Her main research interest is focused on the development of electrochemical sensors and biosensors.
Dr. Xinyan Tracy Cui received her B.E. (1994) and M.S. (1997) from Tsinghua University, Beijing, China, and Ph.D. in Macromolecular Science and Engineering (2002) from University of Michigan, Ann Arbor. Immediately after graduation, she worked for Unilever Research as a research scientist. In 2003, he joined the faculty of Department of Bioengineering at University of Pittsburgh as Assistant Professor and was appointed as Associate Professor in 2010 and Bicentennial Alumni Faculty Fellow in 2012. Her research interests lie in neural engineering with special focuses on neural electrode-tissue interface, neural tissue engineering, drug delivery and biosensor.
Dr. Xiliang Luo received his PhD degree from Nanjing University in 2005. He then worked as a postdoctoral fellow in Dublin City University, Arizona State University and the University of Pittsburgh successively. In 2011, he became a research assistant professor in the Department of Bioengineering, University of Pittsburgh and a senior Marie Curie Fellow in the Department of Chemistry, University of Oxford. He then joined the Qingdao University of Science and Technology at the end of 2011 as a Taishan Scholar professor. His scientific interests are focused on biochemical analysis, nanobiosensing, electrochemistry and conducting polymers.