- Email: [email protected]
Studies on the electrocatalytic oxidation of dopamine at phosphotungstic acid–ZnO spun fiber-modified electrode
Sensors and Actuators B 185 (2013) 651–657
Contents lists available at SciVerse ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
Studies on the electrocatalytic oxidation of dopamine at phosphotungstic acid–ZnO spun fiber-modified electrode Jingping Wu a,b , Fan Yin a,∗ a b
Department of Chemistry and Materials Engineering, Changshu Institute of Technology, Changshu 215500, Jiangsu, China Department of Pharmacy, Medical College of Soochow University, Suzhou 215123, Jiangsu, China
a r t i c l e
i n f o
Article history: Received 31 January 2013 Received in revised form 11 May 2013 Accepted 16 May 2013 Available online 25 May 2013 Keywords: Electrospinning Micro/nanofiber Phosphotungstic acid Dopamine sensor Electrocatalysis
a b s t r a c t A novel and selective electrochemical sensor was developed for the determination of dopamine (DA) based on phosphotungstic acid (PWA)–zinc oxide (ZnO) electrospun fibers. The fibers were constructed in situ on a Pt electrode by using electrospinning technology and succedent heat treatment. The obtained fibers were characterized by SEM, FTIR, and XRD. The electrochemical properties of PWA–ZnO fibers modified electrode and its electrocatalysis for DA electro-oxidation were investigated by cyclic voltammetry and differential pulse voltammetry. The stability of PWA–ZnO fibers was excellent because PWA was embedded in the fibers, which can solve the problem of PWA loss during experiment. According to large surface area of PWA doped ZnO fibers, the modified electrode showed excellent electrocatalytic activity toward the oxidation of DA in the phosphate buffer solution (pH 5.0). A linear relationship between the current response and the concentration of DA ranging from 1.9 × 10−7 to 4.5 × 10−4 M was obtained with a detection limit of 0.089 M at pH 5.0. The DA can be determined in the presence of ascorbic acid (AA) because two compounds were well-separated with a potential difference of 0.36 V on the modified electrode. Based on its excellent electrochemical performance and ease of preparation, the proposed electrode may provide a promising alternative in routine sensing applications. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Electrochemical sensing technique has been recognized as one of efficient methods for the determination of target compounds due to its characteristics of high sensitivity, fast response, easy miniaturization and integration [1,2]. Biomaterials modified electrodes have gained special focus based on their advantage of excellent selectivity in recent decades [3]. Unfortunately, these biomaterials, such as enzyme and antibody, were not favorable for long-term detection owing to their inherent disadvantage, e.g. poor stability, short life span. Moreover, high price of these biomaterials also limited their applications [4]. To overcome these drawbacks, considerable efforts have been oriented to construction of electrochemical sensors based on developing novel electroactive materials with good catalytic activity and stability. Quite a number of important achievements were obtained, such as the non-enzymatic glucose sensor based on various nanoscale semiconducting metal oxides [5–7]. Heteropoly acids (HPAs) have been investigated extensively on both fundamental research and technical applications because of their remarkable catalytic performance and stability [8,9].
∗ Corresponding author. Tel.: +86 139 13686373; fax: +86 512 52251842. E-mail address: [email protected] (F. Yin). 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.05.052
Recently, researchers found that the redox potential of HPAs could be modulated by regulating heteroatom or coordination atom on HPAs structure according to application requirements. The design and synthesis of novel HPAs has become a hotspot in recent years. These prominent characteristics make HPAs a good candidate to serve as catalysts and construct highly sensitive electrochemical sensors. Various techniques including electro-deposition [10], self-assembly [11], and electrostatic absorption [12] have been developed to immobilize HPAs on electrodes surface. However, Ramesh Kumar et al. [13] stated that the major disadvantages of HPAs as a material for electrode modification lie in the low surface area and high solubility in experiment, which reduces sensitivity and stability of these electrodes in analytical application. Some methods have been adopted to solve these problems, such as loading HPAs on nano-materials surface. Maiyalagan [14] has prepared silicotungstic acid/Pt–Ru nanoparticles and used this material to construct an electrochemical sensor for the detection of methanol. Unfortunately, nanoparticles with large surface energy were prone to aggregate during immobilization of them on electrode surface, which reduced the electro-active area of HPAs and sensitivity of the sensor for determination of target molecules. One-dimensional micro/nanofibres membrane with reticular structure may be one of suitable materials for immobilization of HPAs, which not only improve the catalytic activity of HPAs-modified nanofibres but also sort out the problem of agglomeration. To the best of our
652
J. Wu, F. Yin / Sensors and Actuators B 185 (2013) 651–657
knowledge, there were few literatures using micro/nanofibres membrane as supporter for immobilization of HPAs. Electrospinning has recently been reported as a convenient and effective technology for fabricate micro/nanofibres [15]. The obtained fibers exhibited peculiar and fascinating electrochemical performances because of large surface-to-volume ratios and its reticular structure [16]. In this research, phosphotungstic acid (PWA) was selected to be a model HPAs for construction of composite fibers by incorporating it into electrospinning fibers, and the composite fibers was then employed as electro-active material to fabricate a electrochemical sensor. Dopamine (DA) is a ubiquitous neurotransmitter molecule of catecholamines in mammalian brain tissues, and a decrease in its concentration would be related with brain disorders such as Schizophrenia, Parkinson’s disease, and HIV infection [17,18]. The determination of DA plays an important role in various research areas such as the neurophysiology, the quality of medicines, and the mechanism of medicines. Since there are many publications about the determination of DA, in this research, DA was chosen as a target material to estimate the availability of the PWA doping electrospinning fibers modified electrode by comparing with DA sensors that electrodes were modified with other electro-active materials. In this paper, a novel PWA–ZnO fibers modified electrode was fabricated by using electrospinning technique for the determination of DA in the presence of ascorbic acid (AA). The morphology and structure of obtained fibers were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD). The direct electrochemical behavior of PWA–ZnO fibers membrane modified Pt (PWA–ZnO/Pt) electrode was studied for the first time. The electrocatalytic oxidation of DA on PWA–ZnO/Pt electrode was also investigated using differential pulse voltammetry. Results obtained with the PWA–ZnO modified electrode are presented in this paper and discussed in detail. 2. Experimental 2.1. Chemicals and reagents DA was obtained from Sigma (>99.0%). DA hydrochloride injection solution was obtained from Wuhan Grand Pharmaceutical Group Co., Ltd. (Wuhan, China). AA, acetic acid, zinc acetate [Zn(Ac)2 ], PWA and poly(vinyl alcohol) (PVA, degree of polymerization = 1750 ± 50, degree of hydrolysis = 98%) were purchased from Sinopharm Chemical Reagent Co., Ltd. (China). Phosphate-buffered solutions (PBS) were prepared from stock solution of 0.1 M K2 HPO4 and 0.1 M KH2 PO4 . All reagents were of analytical grade or better. Highly pure Pt wire with diameter of 1.0 mm and working length of 3.0 cm was used to construct working electrode. The electrode area is about 0.094 cm2 . Double distilled water was used for all experiments. 2.2. Instrumentation During electrospinning, a high-voltage power (ES3OP-5w/DDP; Suzhou, China) was applied to polymer in a syringe (781101; KD Scientific, USA) through an alligator clip attached to the syringe needle. Thermal treatment was performed using a muffle furnace (GSL-1300X; Hefei, China). The obtained fibers were characterized using an SEM system (KYKY2800, China) at an accelerating voltage of 15.0 kV, an FTIR system (NICOLET 380, Thermo, USA) using KBr pellets and an XRD Analyzer (Shimadzu XRD 6000, Japan). Voltammetric experiments, such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV), were performed with a CHI 660C electrochemical analyzer (Chenhua, Shanghai, China)
using a personal computer to control measurements and treat data. The standard three-electrode system consisted of a platinum sheet as the auxiliary electrode, a saturated calomel electrode as the reference electrode, and the PWA–ZnO/Pt electrode as the working electrode (˚ 0.1 cm × 3 cm). After each experiment, the PWA–ZnO/Pt electrode was washed in 50 mL PBS buffer (pH 5.0) thoroughly and used for next examination. All measurements were conducted at room temperature (25 ◦ C ± 1 ◦ C). 2.3. Fabrication of PWA–ZnO/Pt electrode The precursor solution was prepared according to the following steps. First, PVA (9%, w/v) colloidal solution was prepared by dissolving 2.7 g PVA grains in 30 mL acetic acid (2%, v/v) at 90 ◦ C with 4 h continuous stirring. Then, 1.2 g PWA and 1.2 g Zn(Ac)2 were added into 10 mL distilled water, and the solution was sonicated for 10 min to dissolve the grains completely. Finally, the obtained solution was added into the PVA solution, and the mixture was stirred for 2 h and kept in a water bath maintained at 50 ◦ C to form a homogeneous and viscous precursor solution. Before modification, the bare Pt electrode was well polished with aqueous slurries of alumina powder (0.05 m), rinsed, ultrasonicated in double distilled water, and dried under a stream of high purity nitrogen and ready for use. The as-prepared precursor solution was loaded into a syringe and connected to the high-voltage power supply. Several key operational parameters, such as the flow rate, collection distance, and applied potential, were examined and optimized according to the morphology of obtained fibers. In brief, 20.0 kV of voltage was applied to the syringe needle and collector. The precursor solution was delivered to the blunt needle tip via syringe pump to control flow rate of 5 L/min. The collection distance between the syringe tip and collector was 20 cm. Under the above fixed electrospinning conditions, the acquisition time of fibers was about 30 to obtain sufficiently thick membrane on the surface of Pt electrode that was connected to the collector. After electrospinning and air drying, the obtained fibers modified electrode was treatment at 80 ◦ C for 10 h. Then, the electrode was calcined for 2 h at 400 ◦ C at a heating rate of 5 ◦ C/min under air atmosphere. 3. Results and discussion 3.1. Characteristics of PWA–ZnO fibers The morphologies of as-prepared uncalcined and calcined composite fibers were examined by SEM and shown in Fig. 1. Uniform and continuous PWA–Zn(Ac)2 –PVA fibers were obtained from electrospinning (Fig. 1A). After calcinations of the obtained fibers, a PWA–ZnO fibers membrane was formed with a decrease of its average diameter (Fig. 1B). This phenomenon could be attributed to the elimination of PVA and the decomposition of Zn(Ac)2 . The structure of the fibers membrane was reticular, which improved the fibers’ inflexibility and provided even a larger accessible surface area for the subsequent electrochemical catalytic oxidation of target molecules. FTIR spectra were used to characterize the loading of PWA into ZnO fibers and shown in Fig. 2. The fibers membrane was powderized and mixed with KBr. The intense band at 520.9 cm−1 may be assigned to the Zn–O stretching (Fig. 2 (curve a)), indicating that Zn(Ac)2 had been converted into ZnO by calcination. The fundamental vibrational modes of the PWA Keggin cluster structure were demonstrated in Fig. 2 (curve b). The peaks at 1081.1, 980.8, 892.0, and 819.8 cm−1 can be attributed to the stretching vibrations of P Oa , W Ot terminal oxygen atoms, W Ob W oxygen-bridges, and W Oc W oxygen-bridges, respectively, related to the Keggin
J. Wu, F. Yin / Sensors and Actuators B 185 (2013) 651–657
653
Fig. 3. XRD spectrogram of PWA–ZnO fibers.
Fig. 3. The ZnO pattern was predominant in the composite nanomaterial (Fig. 3). The formation of hexagonal crystalline ZnO was revealed by the diffraction peaks at 2 values of 34.68◦ , 36.46◦ , 37.72◦ , 46.14◦ , 62.12◦ , 65.16◦ , and 68.38◦ corresponding to the (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 0 3), (2 0 2), and (1 1 2) crystal planes, respectively. These values were consistent with the well-known observation that one-dimensional ZnO nanostructures (JCPDS 361451) prefer to grow along the c-axis. The diffraction peaks located at 20–30◦ were attributed to the Keggin ion of PWA, indicating that the tungstate is highly dispersed on the uniform ZnO fibers. In addition, the PWA embedded in ZnO did not change their crystal structure. 3.2. Electrochemical properties of PWA–ZnO/Pt electrode Fig. 1. SEM images of PWA–Zn(Ac)2 –PVA fibers before (A) and after (B) calcination.
ion [19]. FTIR spectrum of PWA–ZnO (Fig. 2 (curve c)) indicated that PWA has been incorporated into ZnO fibers successfully, and Keggin structure of PWA remained unaltered when supported on spun fibers. The crystal structure and constituent of the as-prepared PWA–ZnO fibers were further characterized by XRD and shown in
Fig. 2. FTIR spectra of spun fibers after calcination: (a) ZnO, (b) PWA, and (c) PWA–ZnO.
CV is an effective method for probing the feature of a surfacemodified electrode. Fig. 4 compared CVs of Pt electrodes with different modifications in 0.1 M PBS buffer (pH 5.0). No redox peak was observed in potential range from −0.2 V to 0.6 V on the ZnO/Pt electrode. Poor redox peaks with potential values of Epc = 0.184 V and Epa = 0.270 V were observed at the PWA–PVA/Pt electrode, suggesting that the PWA was embedded in PVA fibers and the sluggish electron transfer was occurred at the interface. This phenomenon may be due to the poor conductivity of PVA fibers that inhibited electron transfer between PWA and electrode. The PWA–ZnO/Pt
Fig. 4. Cyclic voltammograms of Pt electrode modified with ZnO, PWA–PVA, and PWA–ZnO in 0.1 M of PBS (pH 5.0) solution at a scan rate of 50 mV/s.
654
J. Wu, F. Yin / Sensors and Actuators B 185 (2013) 651–657
The kinetics of the electrode reaction was investigated by evaluating the effect of scan rate on oxidation peak current and peak potential. As shown in Fig. 5, for the scan rates in the range of 50–500 mV/s, peak potentials did not change remarkably with increasing scan rates. Peak currents of modified electrode increased obviously with the increase of scan rates. Linear relationships are established between peak currents and scan rates, indicating the surface-controlled mechanism at the PWA–ZnO/Pt electrode and the successful immobilization of PWA–ZnO fibers membrane on Pt electrode surface. 3.3. Effects of supporting electrolyte pH
Fig. 5. Cyclic voltammograms of the PWA–ZnO/Pt electrode at various scan rates in 0.1 M PBS (pH 5.0) solution. The inset represents the plots of the current versus scan rate.
electrode exhibited a well-defined pair of peaks corresponding to the reduction of heteropoly acid to heteropoly blue. The peak current of PWA–ZnO/Pt electrode was much higher than those obtained at PWA–PVA/Pt electrode, indicating that the PWA was attached effectively on the ZnO fibers’ surface with high loading and the semiconductor ZnO on the Pt electrode provided electron conductor between PWA and electrode surface. These characteristics enhanced electrocatalytic activity of PWA–ZnO fibers modified Pt electrode significantly.
Because the reduction of HPA is accompanied by protonation and the stability of HPA might be affected by pH, effects of pH on the PWA–ZnO/Pt electrode were investigated in 0.1 M PBS buffer containing 0.5 mM DA with different pH by using DPV method. The peak potential for redox couple shifted to more negative direction with the increasing pH (Fig. 6A). Plot of the potential of the redox peak versus pH for the PWA–ZnO/Pt showed good linearity from pH 2.0 to pH 9.0, with a slope of −54.6 mV/pH [Fig. 6B (curve 1)], which was close to the theoretical value of −59 mV/pH for the 2e− /2H+ redox process [20]. This phenomenon indicated that the oxidation of DA accompanied by the separation of two H+ from the phenolic hydroxyl group. The highest peak current value was obtained in pH 5.0 (Fig. 6B curve 2), and the voltammogram shape was well defined (Fig. 6A). Along with higher pH, the lower proton concentration of the solution should reduce the response current. Moreover, the stability of PWA was worse in higher pH value. Thus, 0.1 M PBS with pH value of 5.0 was chosen as the electrolyte for the determination of DA. 3.4. Electrocatalytic of PWA–ZnO fibers modified electrode to the oxidation of DA The electrocatalytic oxidation of DA on the PWA–ZnO fibers modified electrode was investigated using CV in a PBS buffer (pH 5.0) and shown in Fig. 7. With a PWA–ZnO/Pt electrode as working electrode, the CV plot exhibited a pair of quasi-reversible anodic and cathodic peaks caused by redox of immobilized PWA when there was no DA in buffer. An obvious increase of oxidation peak currents and a decrease of reduction peak currents of PWA redox were observed after addition of DA solution to electrochemical cell (Fig. 7). Results showed that the immobilized PWA demonstrated excellent electro-catalytic responses to DA oxidation.
Fig. 6. (A) DPV behavior of PWA–ZnO/Pt to 0.5 mM DA. PBS was used from pH 2.0 to pH 9.0. (B) Relationship charts of (1) pH and potential; and (2) pH and peak current.
Fig. 7. Cyclic voltammograms of PWA–ZnO/Pt electrode in PBS (0.1 M, pH 5.0) at a scan rate of 50 mV/s. Curves for different concentrations of H2 O2 : no DA; 5 mM; 10 mM; 15 mM; 20 mM; 25 mM; 30 mM.
J. Wu, F. Yin / Sensors and Actuators B 185 (2013) 651–657
655
Table 1 Comparison of the performance of different DA sensors. Modified electrode
Linear range (M)
Detection limit (M)
References
Poly-l-serine film/CPE HCNTs/GCE (PDDA-[PSS-MWCNTs])n /Gr Poly-acid chrome blue K/GCE p-Nitrobenzenazo resorcinol/GCE CILE OPFP-graphite powder SDS-CMC/CPE Poly-Evans Blue/GCE PAT-Aunano -ME PWA–ZnO NFs/Pt
5.0 × 10−5 2.5 × 10−6 5.0 × 10−5 1.0 × 10−6 5.0 × 10−6 2.0 × 10−6 1.0 × 10−5 1.0 × 10−6 1.0 × 10−5 1.9 × 10−7
0.05 0.80 0.15 0.50 0.30 1.00 5.00 0.25 0.22 0.089
[21] [22] [23] [24] [25] [26] [27] [28] [29] This paper
to 3.0 × 10−4 to 1.05 × 10−4 to 3.5 × 10−4 to 2.0 × 10−4 to 2.5 × 10−5 to 1.5 × 10−3 to 2.0 × 10−4 to 1.0 × 10−5 to 5.0 × 10−5 to 4.5 × 10−4
Because of its higher current sensitivity and better resolution compared with CV, DPV was used in DA test. After addition of DA into the electrochemical cell with a PWA–ZnO fibers modified Pt electrode as working electrode, an obvious increase of the DVP peaks was observed (Fig. 8). The linear regression equation was calibrated as I (A) = −62.36C (mM) − 0.4266 (C: 1.9 × 10−4 to 4.5 × 10−1 ) with the correlation coefficient of R = 0.9996. The detection limit (S/N ratio 3.0) was found to be 0.089 M. The comparison of DA determination on the proposed electrode and on previously reported electrodes was summarized in Table 1. The PWA–ZnO/Pt electrode exhibits improved or comparable performance for DA determination.
Sensitivities of PWA–ZnO/Pt for determination of DA in the presence and absence of AA were also compared. In the presence of 1.00 mM AA, the dependence of the response currents with the concentrations of DA was linear (Fig. 9B), and the linear regression equation is expressed as I (A) = −60.91C (mM) − 5.27, R = 0.9990. The sensitivity of the sensor for DA determination in the presence of AA is 648.0 A/mM cm2 . It is obvious to note that the sensitivity is similar to the sensitivity for an electrolyte solution contains DA alone (667.2 A/mM cm2 ). Sensitivity ratio of the sensor for DA in absence and in presence 1.00 mM AA was about 0.97, indicating that DA can be determined in the presence of AA by using PWA–ZnO/Pt electrode as working electrode and DPV as electrochemistry technique.
3.5. Selectivity and veracity DA in the central nervous systems coexists with AA, and the presence of electroactive AA might affect the quantitative DA determination because its oxidation potential is close to that of DA in normal electrode [30]. The DPV curves of DA on PWA–ZnO/Pt electrode with different concentrations of DA in 0.1 M PBS (pH 5.0) containing 1.00 mM AA were shown in Fig. 9. The anodic peak potentials for the oxidation of DA and AA on PWA–ZnO/Pt electrode were 0.436 and 0.076 V, respectively (Fig. 9A). DPV peak currents of DA increased linearly with increase of DA concentration while the responses of AA kept almost constant current value, indicating that the determination of DA concentration in the presence of AA at the modified electrode was possible.
Fig. 8. Differential pulse voltammograms of PWA–ZnO/Pt electrode in 0.1 M PBS (pH 5.0) solution to different DA concentrations. Accumulation time: 240 s, pulse amplitude: 50 mV, pulse width: 50 ms, pulse period: 200 ms. Inset: corresponding calibration curve at the modified electrode.
Fig. 9. (A) Differential pulse voltammograms at the PWA–ZnO/Pt electrode in 0.1 M PBS (pH 5.0) containing 1 mM AA in the presence of different concentrations of DA. (B) The plot of current response vs. the concentration of DA.
656
J. Wu, F. Yin / Sensors and Actuators B 185 (2013) 651–657
Table 2 Evaluation of DA content in water by using PWA–ZnO/Pt electrode. Sample
Added (M)
Found (M)
Recovery (%)
1 2 3 4
2.0 × 10−7 5.0 × 10−6 7.0 × 10−5 1.0 × 10−4
1.93 × 10−7 4.94 × 10−6 7.15 × 10−5 1.04 × 10−4
96.5 98.8 102.1 104.0
[3]
[4]
[5]
3.6. Application of the sensor [6]
The standard addition technique was used to evaluate the DA by PWA–ZnO/Pt electrode. The sensor was applied to determine the content of DA with known concentrations in water to investigate accuracy of the sensor (Table 2). The developed PWA–ZnO/Pt electrode exhibited exact recovery results between 96.5% and 104.0%. To illustrate the feasibility of PWA–ZnO/Pt electrode for routine analysis, the electrode was applied to determine DA in dopamine hydrochloride injection solution (10.0 mg/mL DA, 2.0 mL per injection). Each sample was detected several times repeatedly. Results showed that the average value of the injection was about 19.82 mg with relative standard deviation (RSD) 4.0%, which was in accordance with the standard content. The satisfactory results obtained with PWA–ZnO/Pt electrode indicated that proposed sensor can be applied to real sample assay.
[7]
[8]
[9] [10]
[11]
[12]
3.7. Stability and reproducibility [13]
The stability of PWA–ZnO/Pt electrode was investigated using CV. The potential of the working electrode was cycled between −0.2 V and 0.6 V at a potential-scanning rate of 50 mV/s for 20 cycles. After each experiment, the PWA–ZnO/Pt electrode was washed in 50 mL 0.1 M PBS buffer (pH 5.0) thoroughly and used for examination in next day. A gradual decrease of the peak currents (12.5%) was found which compared with initial current values after one month examination. The reproducibility of electrode-to-electrode was also checked by using DPV in PBS with 0.3 mM DA. Six PWA–ZnO/Pt electrodes prepared under similar conditions were tested. The RSD of current responses was 3.39%, confirming that the fabrication method is highly reproducible.
[14]
[15] [16]
[17]
[18]
[19]
4. Conclusion [20]
In summary, PWA–ZnO composite spun fiber was prepared and further employed to fabricate PWA–ZnO/Pt electrode for DA determination. The PWA–ZnO fibers membranes proved to be a promising nanomaterial for electrode modification because of their excellent electro-catalytic activity and high electric conductivity. High selectivity and good sensitivity promoted the PWA–ZnO fibers modified electrode to be an effective electrochemical sensing device for direct DA determination in a real sample. The results indicated that the proposed method for sensor’s modification has remarkable potential for its wide application in clinical diagnosis and pharmaceutical analysis.
[21]
[22]
[23]
[24]
Acknowledgement This work was supported by the National Natural Science Foundation of China (NSFC, No. 20975073).
[25]
[26]
References [1] S.J. Park, H. Boo, T.D. Chung, Electrochemical non-enzymatic glucose sensors, Analytica Chimica Acta 556–57 (2006) 46. [2] F. Cao, S. Guo, H.Y. Ma, et al., Nickel oxide microfibers immobilized onto electrode by electrospinning and calcination for nonenzymatic glucose sensor and
[27]
effect of calcination temperature on the performance, Biosensors and Bioelectronics 26 (2011) 2756–2760. L.C. Jiang, W.D. Zhang, A highly sensitive nonenzymatic glucose sensor based on CuO nanoparticles-modified carbon nanotube electrode, Biosensors and Bioelectronics 25 (2010) 1402–1407. A.L. Sun, J.B. Zheng, Q.L. Sheng, A highly sensitive non-enzymatic glucose sensor based on nickel and multi-walled carbon nanotubes nanohybrid films fabricated by one-step co-electrodeposition in ionic liquids, Electrochimica Acta 65 (2012) 64–69. X. Wang, C.G. Hu, H. Liu, et al., Synthesis of CuO nanostructures and their application for nonenzymatic glucose sensing, Sensors and Actuators B 144 (2010) 220–225. C.C. Li, Y.L. Liu, L.M. Li, et al., A novel amperometric biosensor based on NiO hollow nanospheres for biosensing glucose, Talanta 77 (2008) 455–459. Y. Ding, Y. Wang, L. Su, et al., Electrospun Co3 O4 nanofibers for sensitive and selective glucose detection, Biosensors and Bioelectronics 26 (2010) 542–548. ´ M. Davidovic, ´ et al., Proton and protonic entities in solid U.B. Mioˇc, M. Petkovic, heteropoly compounds: an ab initio calculation of the environmental effect on the H5 O2 + ion, Journal of Molecular Structure 885 (2008) 131–138. M.N. Timofeeva, Acid catalysis by heteropoly acids, Applied Catalysis A-General 256 (2003) 19–35. T. Gan, J.Y. Sun, S.Q. Cao, et al., One-step electrochemical approach for the preparation of grapheme wrapped-phosphotungstic acid hybrid and its application for simultaneous determination or sunset yellow and tartrazine, Electrochimica Acta 74 (2012) 151–157. L. Cheng, J.Y. Liu, S.J. Dong, Layer-by-layer assembly of multilayer films consisting of silicotungstate and a cationic redox polymer on 4-aminobenzoic acid modified glassy carbon electrode and their electrocatalytic effects, Analytica Chimica Acta 417 (2000) 133–142. X. Guo, D.J. Guo, J.S. Wang, et al., Using phosphomolybdic acid (H3 PMo12 O40 ) to efficiently enhance the electrocatalytic activity and CO-tolerance of platinum nanoparticles supported on multi-walled carbon nanotubes catalyst in acidic medium, Journal of Electroanalytical Chemistry 638 (2010) 167–172. C. Ramesh Kumar, P.S. Sai Prasad, N. Lingaiah, Heteropoly tungstate supported on tin oxide catalysts for liquid phase benzylation of anisole with benzyl alcohol, Applied Catalysis A-General 384 (2010) 101–106. T. Maiyalagan, Silicotungstic acid stabilized Pt–Ru nanoparticles supported on carbon nanofibers electrodes for methanol oxidation, International Journal of Hydrogen Energy 34 (2009) 2874–2879. N. Bhardwaj, S.C. Kundu, Electrospinning: a fascinating fiber fabrication technique, Biotechnology Advances 28 (2010) 325–347. D. Shan, S.X. Wang, D.B. Zhu, H.G. Xue, Studies on direct electron transfer and biocatalytic properties of haemoglobin in polyacrylonitrile matrix, Bioelectrochemistry 71 (2007) 198–203. P. Damier, E.C. Hirsch, Y. Agid, A.M. Graybiel, The substantia nigra of the human brain: II. Patterns of loss of dopamine-containing neurons in Parkinson’s disease, Brain 122 (1999) 1437–1448. X.M. Cao, L.Q. Luo, Y.P. Ding, et al., Electrochemical methods for simultaneous determination of dopamine and ascorbic acid using cetylpyridine bromide/chitosan composite film-modified glassy carbon electrode, Sensors and Actuators B 129 (2008) 941–946. K. Srilatha, N. Lingaiah, B.L.A. Prabhavathi Devi, et al., Esterification of free fatty acids for biodiesel production over heteropoly tungstate supported on niobia catalysts, Applied Catalysis A-General 365 (2009) 28–33. S.K. Saha, M. Ali, P. Banerjee, Electron exchange and transfer reactions of heteropoly oxometalates, Coordination Chemistry Reviews 122 (1993) 41–62. S. Chitravathi, B.E. Kumara Swamy, G.P. Mamatha, B.S. Sherigara, Simultaneous electrochemical determination of dopamine and ascorbic acid using poly(lserine) modified carbon paste electrode, Journal of Molecular Liquids 160 (2011) 193–199. R.J. Cui, X.Y. Wang, G.H. Zhang, C. Wang, Simultaneous determination of dopamine, ascorbic acid, and uric acid using helical carbon nanotubes modified electrode, Sensors and Actuators B 161 (2012) 1139–1143. R. Manjunatha, G.S. Suresh, J.S. Melo, S.F. D’Souza, T.V. Venkatesha, Simultaneous determination of ascorbic acid, dopamine and uric acid using polystyrene sulfonate wrapped multiwalled carbon nanotubes bound to graphite electrode through layer-by-layer technique, Sensors and Actuators B 145 (2010) 643–650. R. Zhang, G.D. Jin, D. Chen, X.Y. Hu, Simultaneous electrochemical determination of dopamine, ascorbic acid and uric acid using poly(acid chrome blue K) modified glassy carbon electrode, Sensors and Actuators B 138 (2009) 174–181. X.H. Lin, Y.F. Zhang, W. Chen, P. Wu, Electrocatalytic oxidation and determination of dopamine in the presence of ascorbic acid and uric acid at a poly(p-nitrobenzenazo resorcinol) modified glassy carbon electrode, Sensors and Actuators B 122 (2007) 309–314. A. Safavi, N. Maleki, O. Moradlou, F. Tajabadi, Simultaneous determination of dopamine, ascorbic acid, and uric acid using carbon ionic liquid electrode, Analytical Biochemistry 359 (2006) 224–229. ˜ M. Palomar-Pardavé, et al., Selective G. Alarcón-Angeles, S. Corona-Avenda n, electrochemical determination of dopamine in the presence of ascorbic acid using sodium dodecyl sulfate micelles as masking agent, Electrochimica Acta 53 (2008) 3013–3020.
J. Wu, F. Yin / Sensors and Actuators B 185 (2013) 651–657 [28] L.Q. Lin, J.H. Chen, H. Yao, et al., Simultaneous determination of dopamine, ascorbic acid and uric acid at poly(Evans Blue) modified glassy carbon electrode, Bioelectrochemistry 73 (2008) 11–17. [29] A.I. Gopalan, K.P. Lee, K.M. Manesh, et al., Electrochemical determination of dopamine and ascorbic acid at a novel gold nanoparticles distributed poly(4aminothiophenol modified electrode), Talanta 71 (2007) 1774–1781. [30] H. Yao, Y.Y. Sun, X.H. Lin, et al., Electrochemical characterization of poly(eriochrome black T) modified glassy carbon electrode and its application to simultaneous determination of dopamine, ascorbic acid and uric acid, Electrochimica Acta 52 (2007) 6165–6171.
657
Biographies Jingping Wu is currently studying MS degree at Soochow University. Fan Yin is a professor of the Department of Chemistry and Materials Engineering, Changshu Institute of Technology, PR China. He received his MS and PhD in analytical chemistry from Hunan University, China in 1991 and 2002, respectively. His current fields of interest include biosensor, nanodevice, and nanomaterials.
Contents lists available at SciVerse ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
Studies on the electrocatalytic oxidation of dopamine at phosphotungstic acid–ZnO spun fiber-modified electrode Jingping Wu a,b , Fan Yin a,∗ a b
Department of Chemistry and Materials Engineering, Changshu Institute of Technology, Changshu 215500, Jiangsu, China Department of Pharmacy, Medical College of Soochow University, Suzhou 215123, Jiangsu, China
a r t i c l e
i n f o
Article history: Received 31 January 2013 Received in revised form 11 May 2013 Accepted 16 May 2013 Available online 25 May 2013 Keywords: Electrospinning Micro/nanofiber Phosphotungstic acid Dopamine sensor Electrocatalysis
a b s t r a c t A novel and selective electrochemical sensor was developed for the determination of dopamine (DA) based on phosphotungstic acid (PWA)–zinc oxide (ZnO) electrospun fibers. The fibers were constructed in situ on a Pt electrode by using electrospinning technology and succedent heat treatment. The obtained fibers were characterized by SEM, FTIR, and XRD. The electrochemical properties of PWA–ZnO fibers modified electrode and its electrocatalysis for DA electro-oxidation were investigated by cyclic voltammetry and differential pulse voltammetry. The stability of PWA–ZnO fibers was excellent because PWA was embedded in the fibers, which can solve the problem of PWA loss during experiment. According to large surface area of PWA doped ZnO fibers, the modified electrode showed excellent electrocatalytic activity toward the oxidation of DA in the phosphate buffer solution (pH 5.0). A linear relationship between the current response and the concentration of DA ranging from 1.9 × 10−7 to 4.5 × 10−4 M was obtained with a detection limit of 0.089 M at pH 5.0. The DA can be determined in the presence of ascorbic acid (AA) because two compounds were well-separated with a potential difference of 0.36 V on the modified electrode. Based on its excellent electrochemical performance and ease of preparation, the proposed electrode may provide a promising alternative in routine sensing applications. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Electrochemical sensing technique has been recognized as one of efficient methods for the determination of target compounds due to its characteristics of high sensitivity, fast response, easy miniaturization and integration [1,2]. Biomaterials modified electrodes have gained special focus based on their advantage of excellent selectivity in recent decades [3]. Unfortunately, these biomaterials, such as enzyme and antibody, were not favorable for long-term detection owing to their inherent disadvantage, e.g. poor stability, short life span. Moreover, high price of these biomaterials also limited their applications [4]. To overcome these drawbacks, considerable efforts have been oriented to construction of electrochemical sensors based on developing novel electroactive materials with good catalytic activity and stability. Quite a number of important achievements were obtained, such as the non-enzymatic glucose sensor based on various nanoscale semiconducting metal oxides [5–7]. Heteropoly acids (HPAs) have been investigated extensively on both fundamental research and technical applications because of their remarkable catalytic performance and stability [8,9].
∗ Corresponding author. Tel.: +86 139 13686373; fax: +86 512 52251842. E-mail address: [email protected] (F. Yin). 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.05.052
Recently, researchers found that the redox potential of HPAs could be modulated by regulating heteroatom or coordination atom on HPAs structure according to application requirements. The design and synthesis of novel HPAs has become a hotspot in recent years. These prominent characteristics make HPAs a good candidate to serve as catalysts and construct highly sensitive electrochemical sensors. Various techniques including electro-deposition [10], self-assembly [11], and electrostatic absorption [12] have been developed to immobilize HPAs on electrodes surface. However, Ramesh Kumar et al. [13] stated that the major disadvantages of HPAs as a material for electrode modification lie in the low surface area and high solubility in experiment, which reduces sensitivity and stability of these electrodes in analytical application. Some methods have been adopted to solve these problems, such as loading HPAs on nano-materials surface. Maiyalagan [14] has prepared silicotungstic acid/Pt–Ru nanoparticles and used this material to construct an electrochemical sensor for the detection of methanol. Unfortunately, nanoparticles with large surface energy were prone to aggregate during immobilization of them on electrode surface, which reduced the electro-active area of HPAs and sensitivity of the sensor for determination of target molecules. One-dimensional micro/nanofibres membrane with reticular structure may be one of suitable materials for immobilization of HPAs, which not only improve the catalytic activity of HPAs-modified nanofibres but also sort out the problem of agglomeration. To the best of our
652
J. Wu, F. Yin / Sensors and Actuators B 185 (2013) 651–657
knowledge, there were few literatures using micro/nanofibres membrane as supporter for immobilization of HPAs. Electrospinning has recently been reported as a convenient and effective technology for fabricate micro/nanofibres [15]. The obtained fibers exhibited peculiar and fascinating electrochemical performances because of large surface-to-volume ratios and its reticular structure [16]. In this research, phosphotungstic acid (PWA) was selected to be a model HPAs for construction of composite fibers by incorporating it into electrospinning fibers, and the composite fibers was then employed as electro-active material to fabricate a electrochemical sensor. Dopamine (DA) is a ubiquitous neurotransmitter molecule of catecholamines in mammalian brain tissues, and a decrease in its concentration would be related with brain disorders such as Schizophrenia, Parkinson’s disease, and HIV infection [17,18]. The determination of DA plays an important role in various research areas such as the neurophysiology, the quality of medicines, and the mechanism of medicines. Since there are many publications about the determination of DA, in this research, DA was chosen as a target material to estimate the availability of the PWA doping electrospinning fibers modified electrode by comparing with DA sensors that electrodes were modified with other electro-active materials. In this paper, a novel PWA–ZnO fibers modified electrode was fabricated by using electrospinning technique for the determination of DA in the presence of ascorbic acid (AA). The morphology and structure of obtained fibers were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD). The direct electrochemical behavior of PWA–ZnO fibers membrane modified Pt (PWA–ZnO/Pt) electrode was studied for the first time. The electrocatalytic oxidation of DA on PWA–ZnO/Pt electrode was also investigated using differential pulse voltammetry. Results obtained with the PWA–ZnO modified electrode are presented in this paper and discussed in detail. 2. Experimental 2.1. Chemicals and reagents DA was obtained from Sigma (>99.0%). DA hydrochloride injection solution was obtained from Wuhan Grand Pharmaceutical Group Co., Ltd. (Wuhan, China). AA, acetic acid, zinc acetate [Zn(Ac)2 ], PWA and poly(vinyl alcohol) (PVA, degree of polymerization = 1750 ± 50, degree of hydrolysis = 98%) were purchased from Sinopharm Chemical Reagent Co., Ltd. (China). Phosphate-buffered solutions (PBS) were prepared from stock solution of 0.1 M K2 HPO4 and 0.1 M KH2 PO4 . All reagents were of analytical grade or better. Highly pure Pt wire with diameter of 1.0 mm and working length of 3.0 cm was used to construct working electrode. The electrode area is about 0.094 cm2 . Double distilled water was used for all experiments. 2.2. Instrumentation During electrospinning, a high-voltage power (ES3OP-5w/DDP; Suzhou, China) was applied to polymer in a syringe (781101; KD Scientific, USA) through an alligator clip attached to the syringe needle. Thermal treatment was performed using a muffle furnace (GSL-1300X; Hefei, China). The obtained fibers were characterized using an SEM system (KYKY2800, China) at an accelerating voltage of 15.0 kV, an FTIR system (NICOLET 380, Thermo, USA) using KBr pellets and an XRD Analyzer (Shimadzu XRD 6000, Japan). Voltammetric experiments, such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV), were performed with a CHI 660C electrochemical analyzer (Chenhua, Shanghai, China)
using a personal computer to control measurements and treat data. The standard three-electrode system consisted of a platinum sheet as the auxiliary electrode, a saturated calomel electrode as the reference electrode, and the PWA–ZnO/Pt electrode as the working electrode (˚ 0.1 cm × 3 cm). After each experiment, the PWA–ZnO/Pt electrode was washed in 50 mL PBS buffer (pH 5.0) thoroughly and used for next examination. All measurements were conducted at room temperature (25 ◦ C ± 1 ◦ C). 2.3. Fabrication of PWA–ZnO/Pt electrode The precursor solution was prepared according to the following steps. First, PVA (9%, w/v) colloidal solution was prepared by dissolving 2.7 g PVA grains in 30 mL acetic acid (2%, v/v) at 90 ◦ C with 4 h continuous stirring. Then, 1.2 g PWA and 1.2 g Zn(Ac)2 were added into 10 mL distilled water, and the solution was sonicated for 10 min to dissolve the grains completely. Finally, the obtained solution was added into the PVA solution, and the mixture was stirred for 2 h and kept in a water bath maintained at 50 ◦ C to form a homogeneous and viscous precursor solution. Before modification, the bare Pt electrode was well polished with aqueous slurries of alumina powder (0.05 m), rinsed, ultrasonicated in double distilled water, and dried under a stream of high purity nitrogen and ready for use. The as-prepared precursor solution was loaded into a syringe and connected to the high-voltage power supply. Several key operational parameters, such as the flow rate, collection distance, and applied potential, were examined and optimized according to the morphology of obtained fibers. In brief, 20.0 kV of voltage was applied to the syringe needle and collector. The precursor solution was delivered to the blunt needle tip via syringe pump to control flow rate of 5 L/min. The collection distance between the syringe tip and collector was 20 cm. Under the above fixed electrospinning conditions, the acquisition time of fibers was about 30 to obtain sufficiently thick membrane on the surface of Pt electrode that was connected to the collector. After electrospinning and air drying, the obtained fibers modified electrode was treatment at 80 ◦ C for 10 h. Then, the electrode was calcined for 2 h at 400 ◦ C at a heating rate of 5 ◦ C/min under air atmosphere. 3. Results and discussion 3.1. Characteristics of PWA–ZnO fibers The morphologies of as-prepared uncalcined and calcined composite fibers were examined by SEM and shown in Fig. 1. Uniform and continuous PWA–Zn(Ac)2 –PVA fibers were obtained from electrospinning (Fig. 1A). After calcinations of the obtained fibers, a PWA–ZnO fibers membrane was formed with a decrease of its average diameter (Fig. 1B). This phenomenon could be attributed to the elimination of PVA and the decomposition of Zn(Ac)2 . The structure of the fibers membrane was reticular, which improved the fibers’ inflexibility and provided even a larger accessible surface area for the subsequent electrochemical catalytic oxidation of target molecules. FTIR spectra were used to characterize the loading of PWA into ZnO fibers and shown in Fig. 2. The fibers membrane was powderized and mixed with KBr. The intense band at 520.9 cm−1 may be assigned to the Zn–O stretching (Fig. 2 (curve a)), indicating that Zn(Ac)2 had been converted into ZnO by calcination. The fundamental vibrational modes of the PWA Keggin cluster structure were demonstrated in Fig. 2 (curve b). The peaks at 1081.1, 980.8, 892.0, and 819.8 cm−1 can be attributed to the stretching vibrations of P Oa , W Ot terminal oxygen atoms, W Ob W oxygen-bridges, and W Oc W oxygen-bridges, respectively, related to the Keggin
J. Wu, F. Yin / Sensors and Actuators B 185 (2013) 651–657
653
Fig. 3. XRD spectrogram of PWA–ZnO fibers.
Fig. 3. The ZnO pattern was predominant in the composite nanomaterial (Fig. 3). The formation of hexagonal crystalline ZnO was revealed by the diffraction peaks at 2 values of 34.68◦ , 36.46◦ , 37.72◦ , 46.14◦ , 62.12◦ , 65.16◦ , and 68.38◦ corresponding to the (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 0 3), (2 0 2), and (1 1 2) crystal planes, respectively. These values were consistent with the well-known observation that one-dimensional ZnO nanostructures (JCPDS 361451) prefer to grow along the c-axis. The diffraction peaks located at 20–30◦ were attributed to the Keggin ion of PWA, indicating that the tungstate is highly dispersed on the uniform ZnO fibers. In addition, the PWA embedded in ZnO did not change their crystal structure. 3.2. Electrochemical properties of PWA–ZnO/Pt electrode Fig. 1. SEM images of PWA–Zn(Ac)2 –PVA fibers before (A) and after (B) calcination.
ion [19]. FTIR spectrum of PWA–ZnO (Fig. 2 (curve c)) indicated that PWA has been incorporated into ZnO fibers successfully, and Keggin structure of PWA remained unaltered when supported on spun fibers. The crystal structure and constituent of the as-prepared PWA–ZnO fibers were further characterized by XRD and shown in
Fig. 2. FTIR spectra of spun fibers after calcination: (a) ZnO, (b) PWA, and (c) PWA–ZnO.
CV is an effective method for probing the feature of a surfacemodified electrode. Fig. 4 compared CVs of Pt electrodes with different modifications in 0.1 M PBS buffer (pH 5.0). No redox peak was observed in potential range from −0.2 V to 0.6 V on the ZnO/Pt electrode. Poor redox peaks with potential values of Epc = 0.184 V and Epa = 0.270 V were observed at the PWA–PVA/Pt electrode, suggesting that the PWA was embedded in PVA fibers and the sluggish electron transfer was occurred at the interface. This phenomenon may be due to the poor conductivity of PVA fibers that inhibited electron transfer between PWA and electrode. The PWA–ZnO/Pt
Fig. 4. Cyclic voltammograms of Pt electrode modified with ZnO, PWA–PVA, and PWA–ZnO in 0.1 M of PBS (pH 5.0) solution at a scan rate of 50 mV/s.
654
J. Wu, F. Yin / Sensors and Actuators B 185 (2013) 651–657
The kinetics of the electrode reaction was investigated by evaluating the effect of scan rate on oxidation peak current and peak potential. As shown in Fig. 5, for the scan rates in the range of 50–500 mV/s, peak potentials did not change remarkably with increasing scan rates. Peak currents of modified electrode increased obviously with the increase of scan rates. Linear relationships are established between peak currents and scan rates, indicating the surface-controlled mechanism at the PWA–ZnO/Pt electrode and the successful immobilization of PWA–ZnO fibers membrane on Pt electrode surface. 3.3. Effects of supporting electrolyte pH
Fig. 5. Cyclic voltammograms of the PWA–ZnO/Pt electrode at various scan rates in 0.1 M PBS (pH 5.0) solution. The inset represents the plots of the current versus scan rate.
electrode exhibited a well-defined pair of peaks corresponding to the reduction of heteropoly acid to heteropoly blue. The peak current of PWA–ZnO/Pt electrode was much higher than those obtained at PWA–PVA/Pt electrode, indicating that the PWA was attached effectively on the ZnO fibers’ surface with high loading and the semiconductor ZnO on the Pt electrode provided electron conductor between PWA and electrode surface. These characteristics enhanced electrocatalytic activity of PWA–ZnO fibers modified Pt electrode significantly.
Because the reduction of HPA is accompanied by protonation and the stability of HPA might be affected by pH, effects of pH on the PWA–ZnO/Pt electrode were investigated in 0.1 M PBS buffer containing 0.5 mM DA with different pH by using DPV method. The peak potential for redox couple shifted to more negative direction with the increasing pH (Fig. 6A). Plot of the potential of the redox peak versus pH for the PWA–ZnO/Pt showed good linearity from pH 2.0 to pH 9.0, with a slope of −54.6 mV/pH [Fig. 6B (curve 1)], which was close to the theoretical value of −59 mV/pH for the 2e− /2H+ redox process [20]. This phenomenon indicated that the oxidation of DA accompanied by the separation of two H+ from the phenolic hydroxyl group. The highest peak current value was obtained in pH 5.0 (Fig. 6B curve 2), and the voltammogram shape was well defined (Fig. 6A). Along with higher pH, the lower proton concentration of the solution should reduce the response current. Moreover, the stability of PWA was worse in higher pH value. Thus, 0.1 M PBS with pH value of 5.0 was chosen as the electrolyte for the determination of DA. 3.4. Electrocatalytic of PWA–ZnO fibers modified electrode to the oxidation of DA The electrocatalytic oxidation of DA on the PWA–ZnO fibers modified electrode was investigated using CV in a PBS buffer (pH 5.0) and shown in Fig. 7. With a PWA–ZnO/Pt electrode as working electrode, the CV plot exhibited a pair of quasi-reversible anodic and cathodic peaks caused by redox of immobilized PWA when there was no DA in buffer. An obvious increase of oxidation peak currents and a decrease of reduction peak currents of PWA redox were observed after addition of DA solution to electrochemical cell (Fig. 7). Results showed that the immobilized PWA demonstrated excellent electro-catalytic responses to DA oxidation.
Fig. 6. (A) DPV behavior of PWA–ZnO/Pt to 0.5 mM DA. PBS was used from pH 2.0 to pH 9.0. (B) Relationship charts of (1) pH and potential; and (2) pH and peak current.
Fig. 7. Cyclic voltammograms of PWA–ZnO/Pt electrode in PBS (0.1 M, pH 5.0) at a scan rate of 50 mV/s. Curves for different concentrations of H2 O2 : no DA; 5 mM; 10 mM; 15 mM; 20 mM; 25 mM; 30 mM.
J. Wu, F. Yin / Sensors and Actuators B 185 (2013) 651–657
655
Table 1 Comparison of the performance of different DA sensors. Modified electrode
Linear range (M)
Detection limit (M)
References
Poly-l-serine film/CPE HCNTs/GCE (PDDA-[PSS-MWCNTs])n /Gr Poly-acid chrome blue K/GCE p-Nitrobenzenazo resorcinol/GCE CILE OPFP-graphite powder SDS-CMC/CPE Poly-Evans Blue/GCE PAT-Aunano -ME PWA–ZnO NFs/Pt
5.0 × 10−5 2.5 × 10−6 5.0 × 10−5 1.0 × 10−6 5.0 × 10−6 2.0 × 10−6 1.0 × 10−5 1.0 × 10−6 1.0 × 10−5 1.9 × 10−7
0.05 0.80 0.15 0.50 0.30 1.00 5.00 0.25 0.22 0.089
[21] [22] [23] [24] [25] [26] [27] [28] [29] This paper
to 3.0 × 10−4 to 1.05 × 10−4 to 3.5 × 10−4 to 2.0 × 10−4 to 2.5 × 10−5 to 1.5 × 10−3 to 2.0 × 10−4 to 1.0 × 10−5 to 5.0 × 10−5 to 4.5 × 10−4
Because of its higher current sensitivity and better resolution compared with CV, DPV was used in DA test. After addition of DA into the electrochemical cell with a PWA–ZnO fibers modified Pt electrode as working electrode, an obvious increase of the DVP peaks was observed (Fig. 8). The linear regression equation was calibrated as I (A) = −62.36C (mM) − 0.4266 (C: 1.9 × 10−4 to 4.5 × 10−1 ) with the correlation coefficient of R = 0.9996. The detection limit (S/N ratio 3.0) was found to be 0.089 M. The comparison of DA determination on the proposed electrode and on previously reported electrodes was summarized in Table 1. The PWA–ZnO/Pt electrode exhibits improved or comparable performance for DA determination.
Sensitivities of PWA–ZnO/Pt for determination of DA in the presence and absence of AA were also compared. In the presence of 1.00 mM AA, the dependence of the response currents with the concentrations of DA was linear (Fig. 9B), and the linear regression equation is expressed as I (A) = −60.91C (mM) − 5.27, R = 0.9990. The sensitivity of the sensor for DA determination in the presence of AA is 648.0 A/mM cm2 . It is obvious to note that the sensitivity is similar to the sensitivity for an electrolyte solution contains DA alone (667.2 A/mM cm2 ). Sensitivity ratio of the sensor for DA in absence and in presence 1.00 mM AA was about 0.97, indicating that DA can be determined in the presence of AA by using PWA–ZnO/Pt electrode as working electrode and DPV as electrochemistry technique.
3.5. Selectivity and veracity DA in the central nervous systems coexists with AA, and the presence of electroactive AA might affect the quantitative DA determination because its oxidation potential is close to that of DA in normal electrode [30]. The DPV curves of DA on PWA–ZnO/Pt electrode with different concentrations of DA in 0.1 M PBS (pH 5.0) containing 1.00 mM AA were shown in Fig. 9. The anodic peak potentials for the oxidation of DA and AA on PWA–ZnO/Pt electrode were 0.436 and 0.076 V, respectively (Fig. 9A). DPV peak currents of DA increased linearly with increase of DA concentration while the responses of AA kept almost constant current value, indicating that the determination of DA concentration in the presence of AA at the modified electrode was possible.
Fig. 8. Differential pulse voltammograms of PWA–ZnO/Pt electrode in 0.1 M PBS (pH 5.0) solution to different DA concentrations. Accumulation time: 240 s, pulse amplitude: 50 mV, pulse width: 50 ms, pulse period: 200 ms. Inset: corresponding calibration curve at the modified electrode.
Fig. 9. (A) Differential pulse voltammograms at the PWA–ZnO/Pt electrode in 0.1 M PBS (pH 5.0) containing 1 mM AA in the presence of different concentrations of DA. (B) The plot of current response vs. the concentration of DA.
656
J. Wu, F. Yin / Sensors and Actuators B 185 (2013) 651–657
Table 2 Evaluation of DA content in water by using PWA–ZnO/Pt electrode. Sample
Added (M)
Found (M)
Recovery (%)
1 2 3 4
2.0 × 10−7 5.0 × 10−6 7.0 × 10−5 1.0 × 10−4
1.93 × 10−7 4.94 × 10−6 7.15 × 10−5 1.04 × 10−4
96.5 98.8 102.1 104.0
[3]
[4]
[5]
3.6. Application of the sensor [6]
The standard addition technique was used to evaluate the DA by PWA–ZnO/Pt electrode. The sensor was applied to determine the content of DA with known concentrations in water to investigate accuracy of the sensor (Table 2). The developed PWA–ZnO/Pt electrode exhibited exact recovery results between 96.5% and 104.0%. To illustrate the feasibility of PWA–ZnO/Pt electrode for routine analysis, the electrode was applied to determine DA in dopamine hydrochloride injection solution (10.0 mg/mL DA, 2.0 mL per injection). Each sample was detected several times repeatedly. Results showed that the average value of the injection was about 19.82 mg with relative standard deviation (RSD) 4.0%, which was in accordance with the standard content. The satisfactory results obtained with PWA–ZnO/Pt electrode indicated that proposed sensor can be applied to real sample assay.
[7]
[8]
[9] [10]
[11]
[12]
3.7. Stability and reproducibility [13]
The stability of PWA–ZnO/Pt electrode was investigated using CV. The potential of the working electrode was cycled between −0.2 V and 0.6 V at a potential-scanning rate of 50 mV/s for 20 cycles. After each experiment, the PWA–ZnO/Pt electrode was washed in 50 mL 0.1 M PBS buffer (pH 5.0) thoroughly and used for examination in next day. A gradual decrease of the peak currents (12.5%) was found which compared with initial current values after one month examination. The reproducibility of electrode-to-electrode was also checked by using DPV in PBS with 0.3 mM DA. Six PWA–ZnO/Pt electrodes prepared under similar conditions were tested. The RSD of current responses was 3.39%, confirming that the fabrication method is highly reproducible.
[14]
[15] [16]
[17]
[18]
[19]
4. Conclusion [20]
In summary, PWA–ZnO composite spun fiber was prepared and further employed to fabricate PWA–ZnO/Pt electrode for DA determination. The PWA–ZnO fibers membranes proved to be a promising nanomaterial for electrode modification because of their excellent electro-catalytic activity and high electric conductivity. High selectivity and good sensitivity promoted the PWA–ZnO fibers modified electrode to be an effective electrochemical sensing device for direct DA determination in a real sample. The results indicated that the proposed method for sensor’s modification has remarkable potential for its wide application in clinical diagnosis and pharmaceutical analysis.
[21]
[22]
[23]
[24]
Acknowledgement This work was supported by the National Natural Science Foundation of China (NSFC, No. 20975073).
[25]
[26]
References [1] S.J. Park, H. Boo, T.D. Chung, Electrochemical non-enzymatic glucose sensors, Analytica Chimica Acta 556–57 (2006) 46. [2] F. Cao, S. Guo, H.Y. Ma, et al., Nickel oxide microfibers immobilized onto electrode by electrospinning and calcination for nonenzymatic glucose sensor and
[27]
effect of calcination temperature on the performance, Biosensors and Bioelectronics 26 (2011) 2756–2760. L.C. Jiang, W.D. Zhang, A highly sensitive nonenzymatic glucose sensor based on CuO nanoparticles-modified carbon nanotube electrode, Biosensors and Bioelectronics 25 (2010) 1402–1407. A.L. Sun, J.B. Zheng, Q.L. Sheng, A highly sensitive non-enzymatic glucose sensor based on nickel and multi-walled carbon nanotubes nanohybrid films fabricated by one-step co-electrodeposition in ionic liquids, Electrochimica Acta 65 (2012) 64–69. X. Wang, C.G. Hu, H. Liu, et al., Synthesis of CuO nanostructures and their application for nonenzymatic glucose sensing, Sensors and Actuators B 144 (2010) 220–225. C.C. Li, Y.L. Liu, L.M. Li, et al., A novel amperometric biosensor based on NiO hollow nanospheres for biosensing glucose, Talanta 77 (2008) 455–459. Y. Ding, Y. Wang, L. Su, et al., Electrospun Co3 O4 nanofibers for sensitive and selective glucose detection, Biosensors and Bioelectronics 26 (2010) 542–548. ´ M. Davidovic, ´ et al., Proton and protonic entities in solid U.B. Mioˇc, M. Petkovic, heteropoly compounds: an ab initio calculation of the environmental effect on the H5 O2 + ion, Journal of Molecular Structure 885 (2008) 131–138. M.N. Timofeeva, Acid catalysis by heteropoly acids, Applied Catalysis A-General 256 (2003) 19–35. T. Gan, J.Y. Sun, S.Q. Cao, et al., One-step electrochemical approach for the preparation of grapheme wrapped-phosphotungstic acid hybrid and its application for simultaneous determination or sunset yellow and tartrazine, Electrochimica Acta 74 (2012) 151–157. L. Cheng, J.Y. Liu, S.J. Dong, Layer-by-layer assembly of multilayer films consisting of silicotungstate and a cationic redox polymer on 4-aminobenzoic acid modified glassy carbon electrode and their electrocatalytic effects, Analytica Chimica Acta 417 (2000) 133–142. X. Guo, D.J. Guo, J.S. Wang, et al., Using phosphomolybdic acid (H3 PMo12 O40 ) to efficiently enhance the electrocatalytic activity and CO-tolerance of platinum nanoparticles supported on multi-walled carbon nanotubes catalyst in acidic medium, Journal of Electroanalytical Chemistry 638 (2010) 167–172. C. Ramesh Kumar, P.S. Sai Prasad, N. Lingaiah, Heteropoly tungstate supported on tin oxide catalysts for liquid phase benzylation of anisole with benzyl alcohol, Applied Catalysis A-General 384 (2010) 101–106. T. Maiyalagan, Silicotungstic acid stabilized Pt–Ru nanoparticles supported on carbon nanofibers electrodes for methanol oxidation, International Journal of Hydrogen Energy 34 (2009) 2874–2879. N. Bhardwaj, S.C. Kundu, Electrospinning: a fascinating fiber fabrication technique, Biotechnology Advances 28 (2010) 325–347. D. Shan, S.X. Wang, D.B. Zhu, H.G. Xue, Studies on direct electron transfer and biocatalytic properties of haemoglobin in polyacrylonitrile matrix, Bioelectrochemistry 71 (2007) 198–203. P. Damier, E.C. Hirsch, Y. Agid, A.M. Graybiel, The substantia nigra of the human brain: II. Patterns of loss of dopamine-containing neurons in Parkinson’s disease, Brain 122 (1999) 1437–1448. X.M. Cao, L.Q. Luo, Y.P. Ding, et al., Electrochemical methods for simultaneous determination of dopamine and ascorbic acid using cetylpyridine bromide/chitosan composite film-modified glassy carbon electrode, Sensors and Actuators B 129 (2008) 941–946. K. Srilatha, N. Lingaiah, B.L.A. Prabhavathi Devi, et al., Esterification of free fatty acids for biodiesel production over heteropoly tungstate supported on niobia catalysts, Applied Catalysis A-General 365 (2009) 28–33. S.K. Saha, M. Ali, P. Banerjee, Electron exchange and transfer reactions of heteropoly oxometalates, Coordination Chemistry Reviews 122 (1993) 41–62. S. Chitravathi, B.E. Kumara Swamy, G.P. Mamatha, B.S. Sherigara, Simultaneous electrochemical determination of dopamine and ascorbic acid using poly(lserine) modified carbon paste electrode, Journal of Molecular Liquids 160 (2011) 193–199. R.J. Cui, X.Y. Wang, G.H. Zhang, C. Wang, Simultaneous determination of dopamine, ascorbic acid, and uric acid using helical carbon nanotubes modified electrode, Sensors and Actuators B 161 (2012) 1139–1143. R. Manjunatha, G.S. Suresh, J.S. Melo, S.F. D’Souza, T.V. Venkatesha, Simultaneous determination of ascorbic acid, dopamine and uric acid using polystyrene sulfonate wrapped multiwalled carbon nanotubes bound to graphite electrode through layer-by-layer technique, Sensors and Actuators B 145 (2010) 643–650. R. Zhang, G.D. Jin, D. Chen, X.Y. Hu, Simultaneous electrochemical determination of dopamine, ascorbic acid and uric acid using poly(acid chrome blue K) modified glassy carbon electrode, Sensors and Actuators B 138 (2009) 174–181. X.H. Lin, Y.F. Zhang, W. Chen, P. Wu, Electrocatalytic oxidation and determination of dopamine in the presence of ascorbic acid and uric acid at a poly(p-nitrobenzenazo resorcinol) modified glassy carbon electrode, Sensors and Actuators B 122 (2007) 309–314. A. Safavi, N. Maleki, O. Moradlou, F. Tajabadi, Simultaneous determination of dopamine, ascorbic acid, and uric acid using carbon ionic liquid electrode, Analytical Biochemistry 359 (2006) 224–229. ˜ M. Palomar-Pardavé, et al., Selective G. Alarcón-Angeles, S. Corona-Avenda n, electrochemical determination of dopamine in the presence of ascorbic acid using sodium dodecyl sulfate micelles as masking agent, Electrochimica Acta 53 (2008) 3013–3020.
J. Wu, F. Yin / Sensors and Actuators B 185 (2013) 651–657 [28] L.Q. Lin, J.H. Chen, H. Yao, et al., Simultaneous determination of dopamine, ascorbic acid and uric acid at poly(Evans Blue) modified glassy carbon electrode, Bioelectrochemistry 73 (2008) 11–17. [29] A.I. Gopalan, K.P. Lee, K.M. Manesh, et al., Electrochemical determination of dopamine and ascorbic acid at a novel gold nanoparticles distributed poly(4aminothiophenol modified electrode), Talanta 71 (2007) 1774–1781. [30] H. Yao, Y.Y. Sun, X.H. Lin, et al., Electrochemical characterization of poly(eriochrome black T) modified glassy carbon electrode and its application to simultaneous determination of dopamine, ascorbic acid and uric acid, Electrochimica Acta 52 (2007) 6165–6171.
657
Biographies Jingping Wu is currently studying MS degree at Soochow University. Fan Yin is a professor of the Department of Chemistry and Materials Engineering, Changshu Institute of Technology, PR China. He received his MS and PhD in analytical chemistry from Hunan University, China in 1991 and 2002, respectively. His current fields of interest include biosensor, nanodevice, and nanomaterials.