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copper oxide decorated electrode for high performance nonenzymatic glucose detection
Journal of Electroanalytical Chemistry 841 (2019) 1–9
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3D porous structured polyaniline/reduced graphene oxide/copper oxide decorated electrode for high performance nonenzymatic glucose detection Lu Fanga, Qin Zhub, Yu Caib, Bo Liangb, Xuesong Yeb, a b
T
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College of Life Information Science and Instrument Engineering, HangZhou DianZi University, Hangzhou, China Biosensor National Special Laboratory, College of Biomedical Engineering & Instrument Science, ZheJiang University, Hangzhou, China
ARTICLE INFO
ABSTRACT
Keywords: Non-enzymatic sensor Copper oxide Polyaniline nanofibers Reduced graphene oxide Glucose sensor
In this study, graphene oxide (GO) was directly co-deposited with polyaniline (PANI) on a Pt electrode and a 3D cluster structure of GO with wrinkled and rough surface was formed during the electro-polymerization and deposition process. Results of Raman spectra, X-ray photoelectron spectroscopy (XPS) showed that strong conjugated interactions had formed between GO clusters and PANI nanofibers. After GO was reduced, XPS measurements and electrochemical impedance spectra (EIS) studies indicated that most of the oxygen functional groups in GO were successfully removed and the conductivity of the composite material was dramatically increased. The morphology and structure of the prepared Pt/PANI/rGO/CuO electrodes were characterized by scanning electron microscopy (SEM) and the electrochemical response of the proposed electrodes in presence of glucose was investigated. Results showed that the 3D structure of rGO clusters greatly increased its effective surface area and improved the electronic transmission efficiency of the composite nanomaterial thus the Pt/ PANI/rGO/CuO modified electrodes displayed much higher electrocatalytic activity than the Pt/PANI/CuO modified electrodes towards glucose, exhibiting a high sensitivity of 1252 μA mM−1 cm−2, a fast response time of < 3 s, a low detection limit of 1.5 μM (S/N = 3) and a wide linear range from 0 mM to 13 mM. The Pt/PANI/ rGO/CuO electrode effectively resisted the effect of interferences such as L-ascorbic acid (AA), acetaminophen (AP) and uric acid (UA) and retained ~ 90% of its initial sensitivity after 15 days.
1. Introduction Over the past few years, various nanostructured metals (e.g., Au [1], Pt [2], Pd [3]), metal alloys (e.g., PtePd [4], CueAg [5], PteAu [6]) and metal oxide (e.g., NiO [7], Co3O4 [8], CuO [9]) have been used to fabricate nonenzymatic glucose sensors due to their excellent catalytic performance. Among these catalysts, CuO nanoparticles (CuONPs) have attracted much attention because of their advantages such as nontoxicity, low cost, simple fabrication technique and good electrochemical activity [10,11]. To enhance the electrocatalytic properties of CuO, a common used method is incorporating conductive materials such as carbon nanotubes (CNTs) [12], conductive polymers (e.g., polyaniline (PANI) [13], polypyrrole [14]) and graphene [15] with CuO to form composite materials. PANI is one of the most widely used conductive polymers in biosensors due to its good conductive property, high stability and ease preparation method [16]. Several composite materials such as metal or metal oxide decorated on PANI arrays have been reported to have high sensitivity to glucose. It has been reported that Au nanoparticles
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deposited on PANI arrays/carbon cloth integrated flexible electrode possessed the ability to electrochemically catalyze the oxidation of glucose and had a good accuracy for real serum samples analysis [17]. NiO/CuO composite nanoparticles [18], PtNPs [19] and NiCo2O4 [20] modified PANI nanofibers also showed similar high sensitivity towards glucose oxidation. Although PANI holds a special position among the conducting polymers and has been widely used in biochemical sensors, its electroactivity can only be retained in acidic media (usually at pH < 3) and tend to lose its conductivity due to deprotonation in neutral or alkaline solution [21–24], limiting its application in alkaline solution in which most of the nonenzymatic glucose sensors are tested. To overcome this limitation, some nanomaterials capable of increasing its conductivity have been combined with PANI to improve its electroactivity in alkaline solution, such as graphene [25], multiwalled carbon nanotubes [26] and graphene oxide (GO) [27,28]. Graphene, a kind of carbonaceous material with good conductivity, large specific surface area and stable chemical properties [29], has also been extensively applied in glucose electrode modification. In many biochemical sensors' applications, graphene, graphene oxide (GO) and
Corresponding author. E-mail addresses: [email protected] (B. Liang), [email protected] (X. Ye).
https://doi.org/10.1016/j.jelechem.2019.04.032 Received 2 January 2019; Received in revised form 20 March 2019; Accepted 9 April 2019 Available online 10 April 2019 1572-6657/ © 2019 Published by Elsevier B.V.
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Scheme 1. Procedure for the fabrication of the Pt/PANI/rGO/CuO electrode.
Fig. 1. SEM micrographs of the surface appearance of the electrodes. (A) Pt/PANI layer, (B) Pt/PANI/CuO layer, (C) Pt/PANI/GO layer, (D) enlarged view of Pt/ PANI/GO layer, (E) Pt/PANI/rGO/CuO layer, (F) EDX spectrum of Pt/PANI/rGO/CuO layer.
reduced graphene oxide (rGO) are decorated on the surface of sensors with a planer 2D structure and improve the sensor's performance [25,30,31]. However, the planer 2D structure and easy-to-aggregate properties of graphene and its derivatives greatly reduce their accessible surface area and active catalytic sites, thereby block their use in practical applications [32–34]. In this study, GO was co-deposited with PANI on the electrode and
formed a 3D cluster structure with wrinkled and rough surface during the electro-polymerization and deposition process. The 3D structure of GO clusters increased its effective surface area and thus improved the electronic transmission efficiency of the composite nanomaterial. After GO was reduced, Cu nanoparticles were deposited on the PANI/rGO layer and oxidized into CuO subsequently, then a non-enzymatic electrochemical glucose biosensor was finally constructed. The interaction 2
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biosensor exhibited substantial electrocatalytic activity towards glucose, and showed an excellent analytical performance with the sensitivity of 1252 μA mM−1 cm−2 and wide linear range from 0 mM to 13 mM towards glucose. These high performances made it a promising application candidate in nonenzymatic glucose detection. 2. Experimental 2.1. Materials Platinum electrode was purchased from Chinstrument Co., Ltd. (Shanghai, China). Aqueous solution of graphene oxide (Lateral Dimension: 50–200 nm, Concentration: 2 mg/ml) was purchased from Nanjing XFNANO Materials Tech. Co. Ltd. (Nanjing, China). Copper (II) nitrate hexahydrate (Cu(NO3)2·6 H2O), potassium nitrate (KNO3), sodium hydroxide (NaOH) and hydrochloric acid (HCl) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Chloroplatinic acid, Ascorbic acid (AA), acetaminophen (DA), and uric acid (UA) were purchased from Sigma-Aldrich Co., LLC. (Shanghai, China). All reagents were of analytical grade and all aqueous solutions were prepared with deionized (DI) water. Counter electrode (Pt electrode) and Reference electrode (KCl solution saturated Ag/AgCl electrode) were bought from Shanghai Chenhua Instrument Company (Shanghai Chenhua Co., China).
Fig. 2. Raman spectra of Pt/PANI, Pt/PANI/GO, Pt/PANI/rGO and Pt/PANI/ rGO/CuO layers.
between nanomaterials, the morphologies and electrochemical activities such as sensitivity, linearity, selectivity, repeatability and stability of the prepared Pt/PANI/rGO/CuO glucose sensor were tested. This
Fig. 3. (A) XPS spectra of Pt/PANI, Pt/PANI/GO and Pt/PANI/rGO, (B) C 1s XPS spectra of Pt/PANI, (C) C 1s XPS spectra of Pt/PANI/GO, (D) C 1s XPS spectra of Pt/ PANI/rGO. 3
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Fig. 4. (A) CVs for different electrodes in 0.1 M NaOH without glucose, (B) CVs for different electrodes in 0.1 M NaOH with 4 mM glucose, (C) Reduction CV curves of Pt/PANI/GO electrode in 1 M NaOH, (D) The electrochemical impedance spectra of Pt, Pt/PANI, Pt/PANI/GO, Pt/PANI/rGO and Pt/PANI/rGO/CuO electrodes in 0.1 M NaOH solution over a frequency range of 0.01 to 100 kHz.
50 mV·s−1 for 10 cycles. After that, the Pt/PANI/GO electrodes were rinsed with DI water to wash away the residual hydrochloric acid. To increase the conductivity of the PANI/GO layer, the Pt/PANI/GO electrodes were reduced in an oxygen-free 1.0 M NaOH solution to transform GO into rGO. The electrochemical reduction process was performed by applying a scanning potential from −1.1 V to 0 V with a scan rate of 25 mV·s−1 for 8 cycles. CuO nanoparticles were deposited on the Pt/PANI/rGO electrodes surface by an electrochemical method. Firstly, 12 cycles of cyclic voltammetry between −0.7 to 0.8 V with a scan rate of 25 mV·s−1 were first applied to the Pt/PANI/rGO electrodes in 0.01 M Cu(NO3)2 and 0.1 M KNO3 solution for the formation of Cu nanoparticles on the surface of the electrodes. Subsequently, Cu nanoparticles were oxidized to the CuO by applying 14 cycles of cyclic voltammetry from 0 to 0.8 V (50 mV·s−1) in 0.05 M NaOH solution and then washed with DI water. After all these steps, the Pt/PANI/rGO/CuO electrodes had been prepared. Pt/PANI/CuO electrodes were prepared as a control group. The preparation of Pt/PANI/CuO electrodes was almost the same as the Pt/ PANI/rGO/CuO electrodes preparation process except that GO was not added in the first electropolymerization process and the Pt/PANI electrode did not to reduce in NaOH solution. After electropolymerization of PANI, electro-deposition of Cu nanoparticles and Cu oxidation, the Pt/PANI//CuO electrodes had been prepared.
2.2. Apparatus All electrochemical measurements were performed using an electrochemical workstation (μAutolab III, Metrohm, Switzerland) at the room temperature. Glucose concentration changes in the bovine serum samples were measured by a lab accurate glucose and lactate analyzer (Biosen C-Line, EKF, Germany). Scanning electron microscopic (SEM) images and Energy Dispersive X-Ray Spectroscopy (EDX) were collected on a field emission scanning electron microscope (SEM, SIRION FEI, Netherlands). Raman spectra were collected using a laser confocal Raman spectrometer (Horiba Jobin Yvon, LabRAM HR Evolution) with a 532 nm HeeNe laser. X-ray photoelectron spectroscopy (XPS) measurements were performed sing a Thermo Scientific ESCALAB 250Xi spectrometer with a monochromated Al Ka radiation (hv = 1486.6 eV). 2.3. Preparation of the sensor The nonenzymatic glucose sensor was prepared with the process as shown in Scheme 1. Pt electrodes were carefully polished and washed by DI water and ethanol, respectively. Then, the Pt electrodes were dipped in a 1.0 M hydrochloric acid solution containing 0.5 M aniline (Ani) and 0.5 mg/ml GO for electropolymerization of PANI/GO. The PANI/GO electropolymerization was carried out by cyclic voltammetry in the potential window of −0.1 to 1.2 V with the scan rate of 4
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Fig. 5. (A) CVs of the Pt/PANI/rGO/CuO modified electrodes from 0 V to 0.9 V in 0.1 M of NaOH solution at different scan rates, (B) CVs of Pt/PANI/rGO/CuO electrode from −0.5 V to 0.9 V in 0.1 M NaOH solution with various concentrations of glucose, (C) Schematic illustration of the glucose electrocatalytic reaction mechanism on the surface of Pt/PANI/rGO/CuO electrode.
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2.4. Characterization All the electrochemical procedures in this study was performed using a classic three-electrode system including a platinum electrode as the counter electrode, an Ag/AgCl electrode as the reference electrode and a modified platinum electrode as the working electrode. 0.1 M NaOH solution was employed as the supporting electrolyte in the analytical procedure. Electrochemical behaviors of Pt/PANI/rGO/CuO electrode were investigated by cyclic voltammetry in the potential window of −0.5 V to 0.9 V. Electrochemical impedance spectra (EIS) of Pt/PANI, Pt/PANI/GO, Pt/PANI/rGO modified electrodes was measured over a frequency range of 0.01 to 100 KHz. Amperometric detection of glucose was performed under the potential of 0.6 V and continues adding 1 M glucose solution to the supporting electrolyte every 30 s after it reached stable current. 3. Results and discussion 3.1. Morphology and structure of electrode SEM was used to characterize the morphologies of the Pt/PANI, Pt/ PANI/CuO, Pt/PANI/GO and Pt/PANI/rGO/CuO electrode layers. Fig. 1(A) shows the surface appearance of PANI nanofibers. The diameter of the PANI nanofibers is around 100 nm and the length of the nanofibers is about 1 um. The PANI nanofibers represent a well-arranged polymer chain structure with high ratio of surface-to-volume, that is useful for the decorating of CuO particles. Fig. 1(B) shows the surface morphology of the Pt/PANI/CuO layer. As can be seen, the CuO cubic nanoparticles with a uniform size ranged about 500 nm are evenly dispersed on the surface of PANI nanofibers and embedded between them. Fig. 1(C) shows the surface morphology of Pt/PANI/GO layer. As can be seen, the GO clusters, which are uniformly embedded in the PANI nanofibers matrix during the co-deposition process, form a 3D structure with wrinkled surface. Fig. 1(D) shows an enlarged view of Pt/PANI/GO layer, we can see the GO surface covered by short PANI nanofibers. The 3D structure of GO clusters increases its effective surface area compared to the 2D structure. Fig. 1(E) shows the morphology of Pt/PANI/rGO/CuO layer after Cu was deposited and oxidized. The CuO nanoparticles are uniformly dispersed on the surface of rGO clusters and PANI nanofibers. Fig. 1(F) gives the SEM/EDX spectrum of Pt/PANI/rGO/CuO layer. The Au peak comes from the gold sputtering procedure in sample surface processing before SEM. We can confirm from the EDX spectrum that CuO nanoparticles have been deposited on the electrode surface. Raman analysis was performed to study the specific interaction between GO and the PANI nanofibers. Raman spectra of the Pt/PANI layer, Pt/PANI/GO layer and Pt/PANI/rGO/CuO layer are plotted in Fig. 2. Several typical PANI characteristic peaks were observed in the Pt/PANI layer, including 1161 cm−1 (CeH bending vibration of the quinoid rings) [35], 1213 cm−1 (CeH bending vibration of the benzenoid rings), 1485 cm−1 (the stretching vibrations of C]N groups) [36], 1582 cm−1 (C]C stretching of the benzenoid rings) [37,38]. After GO was co-deposited with PANI, a D band peak around 1348 cm−1, which is known as defective band that usually arises from the first order scattering of sp3 hybridized carbon atoms [39], appears in the PANI/GO Raman spectrum. Furthermore, the relatively increase of G band intensity also indicate an increase of stretching vibration of sp2 hybridized C]C bonds [39], which may come from the C]C stretching vibration of graphene. The appearance of D band and increase of G band confirm the existence of strong interactions between GO and the PANI. When GO was reduced, the relative D band intensity of the Pt/ PANI/rGO increased. The increase of ID/IG ratio value of Pt/PANI/rGO indicates the formation of disordered new graphitic domains during the reduction process, suggesting the successful reduction of GO. For Pt/ PANI/rGO/CuO, the decrease of ID/IG ratio may occur due to the repair of defects on rGO surface during the CuO decoration. 5
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Fig. 6. (A) Amperometric titration response of Pt/PANI/rGO/CuO electrode at various concentration of glucose in 0.1 M NaOH, (B) The calibration curve of Pt/ PANI/CuO and Pt/PANI/rGO/CuO electrodes of glucose (0 mM–20 mM) in 0.1 M NaOH.
The XPS spectra of Pt/PANI, Pt/PANI/GO and Pt/PANI/rGO are shown in Fig. 3. As can be seen from Fig. 3(A), among of these presented materials, peaks centered at 285 eV (C 1s), 400 eV (N 1 s) and 534 eV (O 1 s) are all observed from the wide range spectrum, and the N 1 s peak confirms the presence of PANI in the composites. Pure PANI has a small amount of O compared with the composites and after being co-deposited with GO, the O 1s peak intensity of Pt/PANI/GO significantly increases, confirming the combination of PANI and GO. The O 1s peak of Pt/PANI/rGO is much lower than that of Pt/PANI/GO, indicating that most of the oxygen functional groups on the surface of GO of PANI/GO have been eliminated during the reduction process. Fig. 3(B)–(D) shows the deconvoluted C 1s spectra of Pt/PANI, Pt/ PANI/GO and Pt/PANI/rGO, each of which can be curve-fitted into five peak components: CeC group at 284.5 eV [40], C]C group at 285.2 eV, CeN group at 285.9 eV, CeO group at 286.9 eV [41] and C] O group at 287.9 eV [42,43]. The areas of the five C 1s components of Pt/PANI/GO show that the oxygenated C (CeO and C]O components) is about 28% (284.5 eV), while that of PANI/rGO is 13%. These results indicate that most of the oxygen functional groups in GO were successfully removed and the conductivity of GO would be recovered [40,44].
consistent with other studies [45,46]. The GO reduction peak current shows a decreasing trend during the oxidoreduction process from the first cycle to the last cycle, indicating that the most of the oxygen functional groups such as epoxy, carbonyl and hydroxyl groups have been gradually reduced and rGO formed during this procedure. To study the electron transfer ability between electrolyte and the surface of different electrodes, the electrochemical impedance spectra (EIS) of Pt/PANI, Pt/PANI/GO, Pt/PANI/rGO and Pt/PANI/rGO/CuO electrodes were measured in 0.1 M NaOH solution over a frequency range of 0.01 to 100 KHz (shown in Fig. 4(D)). Sodium hydroxide solution was chosen as the electrolyte solution because the conductivity of PANI is very sensitive to the pH of electrolyte solution and the nonenzymatic glucose sensor was finally tested in the alkaline solution. In order to compare the electron transfer capacity of the composite material with and without 3D structured rGO, the electron transfer resistances (RCT) of them were investigated by EIS. As shown Fig. 4(D), the Pt electrode has the most minimum impedance because of the good conductivity of platinum. The Rct of Pt/ PANI/GO electrode (6702 Ω) is smaller than that of Pt/PANI electrode (9772 Ω). As we know, the conductivity of PANI nanofibers could greatly decrease in alkaline solution [40,47], which would reduce the electron transfer efficiency of the electrode. The GO clusters dispersed in PANI nanofibers could reduce electron transfer resistance between CuO nanoparticles and electrode surface. However, the conductivity of Pt/PANI/GO electrode was still not desirable due to the oxygenous groups on the GO surface. After electrochemical reduction in alkaline solution, the Pt/PANI/rGO electrode showed a much smaller Rct (258 Ω) than Pt/PANI/GO electrode (6702 Ω), indicating that most of the oxygenous groups on the GO surface had been removed. The impedance of Pt/PANI/rGO/CuO electrode increased (1950 Ω) after CuO was decorated on the Pt/PANI/rGO surface because CuO is a p-type semiconductor which has poor conductivity [48]. Fig. 5(A) shows the CVs of the Pt/PANI/rGO/CuO modified electrodes from 0 V to 0.9 V in 0.1 M of NaOH solution at different scan rates separately. With the increasing sweep rates from 50 mV s−1 to 350 mV s−1, the oxidation peaks shift positively and the reduction peaks shift negatively. The calibration curve (the inset of Fig. 5A) exhibits that the oxidation peak currents increase linearly with the increasing scan rate with correlation coefficients (R2) of 0.992, indicating that the redox process is a typical surface controlled electrochemical process. Fig. 5(B) shows the CVs of Pt/PANI/rGO/CuO modified electrode from −0.5 V to 0.9 V in 0.1 M NaOH solution with various
3.2. Electrocatalytic performance of electrode Fig. 4(A) and (B) show the CVs for Pt/PANI, Pt/PANI/CuO, Pt/ PANI/GO, Pt/PANI/rGO, Pt/PANI/rGO/Cu and Pt/PANI/rGO/CuO electrodes in 0.1 M NaOH in both absence and presence of glucose (4 mM) with the scan rate of 50 mV·s−1 from −0.5 V to 0.9 V. Compare with the two CVs, we can see that Pt/PANI, Pt/PANI/CuO, Pt/PANI/GO and Pt/PANI/rGO electrodes have no oxidation peak in both absence and presence of glucose. After Cu nanoparticles were deposited and oxidized, the Pt/PANI/rGO/Cu and Pt/PANI/rGO/CuO electrodes show oxidation peaks to glucose at around 0.6 V, indicating that the Cu and CuO nanoparticles are the catalyzer of glucose in these nonenzymatic glucose sensors. Furthermore, the Pt/PANI/rGO/CuO electrode shows a higher oxidation current compared with Pt/PANI/rGO/Cu electrode. Therefore, we chose CuO nanoparticles as the catalyzer in this study. As reported by other studies, electrochemical method can equivalently, uniformly, firmly and steadily reduce graphene oxide to graphene [45]. In this study, the electrochemical reduction of GO was performed by applying −1.1 V to 0 V for eight cycles in 1 M NaOH. Fig. 4(C) shows typical reduction CV curves of Pt/PANI/GO electrode, the GO reduction peak is observed at around −0.9 V, which is 6
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Fig. 7. (A) Reproducibility of the Pt/PANI/rGO/CuO electrodes, (B)The chronoamperometric of glucose on Pt/PANI/rGO/CuO electrode in the presence of interfering species, (C) Stability of Pt/PANI/rGO/CuO electrodes stored under ambient conditions for 15 days.
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Table 1 Determination of glucose concentration in blood serum samples. Sample number 1 2 3 4 5 6
Added (mM) 2 4 6 8 10 12
Measured by our biosensor (mM) 2.01 4 5.89 7.92 9.67 11.15
Recovery (%)
RSD (%, n = 4)
100.5 100 98.17 99 96.7 92.92
3.51 4.23 4.28 3.86 3.92 3.91
concentrations of glucose (from 0 mM to 14 mM). The inset is a calibration curve corresponding to amperometric responses at 0.6 V, exhibiting a linear response up to 14 mM of glucose with correlation coefficients (R2) of 0.996. The electrooxidation of glucose involves the following steps as indicated in Fig. 5(C). First, the Cu(II) in forms of CuO is electrochemically oxidized to a strongly oxidizing Cu(III) in forms of CuOOH under the alkaline conditions during the potential scan [49,50] (Reaction 1). Once glucose is added, it is catalytically oxidized by the CuOOH and produces hydrolyzate gluconic acid as indicated in Reaction 2. The glucose oxidation peak is observed at around 0.6 V and this peak current increased with glucose concentration. 3.3. Amperometric response characteristics of the sensor The responses of Pt/PANI/CuO and Pt/PANI/rGO/CuO electrodes in 0.1 M NaOH in the presence of different glucose concentrations (from 10 μM to 20 mM) were investigated at a constant potential (0.6 V vs. Ag/AgCl at room temperature) while the supporting solution was stirring during the measurements. Fig. 6(A) shows a typical response curve of the Pt/PANI/rGO/CuO electrode and the Pt/PANI/CuO electrode during tests. The inset of Fig. 6(A) shows the response of the Pt/PANI/ rGO/CuO electrodes to low glucose concentrations. As can be seen, the Pt/PANI/rGO/CuO electrodes show much higher response to glucose variation than that of Pt/PANI/CuO electrodes. Moreover, the Pt/ PANI/rGO/CuO electrodes exhibit a much faster response (response time is < 3 s) than Pt/PANI/CuO electrodes (response time is around 10 s). Fig. 6(B) illustrates a plot of current density (mA·cm−2) and calibration curves vs. glucose concentration (mM) of Pt/PANI/CuO and Pt/ PANI/rGO/CuO electrodes. The sensitivity of the Pt/PANI/CuO sensor is 349 μA·mM−1·cm−2 and the linear range is between 0 mM to 14 mM (R2 > 0.994). The sensitivity of the Pt/PANI/rGO/CuO sensor is 1252 μA·mM−1·cm−2 with a glucose detection limit of 1.5 μM (S/ N = 3) and the linear range is between 0 mM to 13 mM (R2 > 0.994). The sensitivity of the Pt/PANI/rGO/CuO sensor is 3.6 times that of the Pt/PANI/CuO sensor which may be due to the higher electron transfer efficiency of the rGO clusters co-deposited in the PANI nanofibers. As we know, the conductivity of PANI nanofibers will greatly decrease in alkaline solution and this will reduce electron transfer efficiency of the nanomaterial. The rGO clusters, which was uniformly dispersed in PANI nanofibers and form a 3D structure during the co-deposition process, could reduce the electron transport resistance between CuO nanoparticles and the electrode surface, thereby increasing the sensitivity and linear range of the sensor. 3.4. Reproducibility, selectivity and stability of the Pt/PANI/rGO/CuO electrode To examine the reproducibility of the Pt/PANI/rGO/CuO electrodes, five electrodes were prepared under the same condition and their chronoamperometric responses to 0–20 mM glucose (with 2 mM glucose concentration increase every step) in 0.1 M NaOH were measured. As shown in Fig. 7(A), the relative standard deviation of the five 7
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Table 2 Compression of this work with some of resent reports for electrochemical glucose detection. Electrode material CuNPs/PRG/SCT CuO-PANI/FTO CuO/Graphene/GCE CuO/MWCNTs Nanoporous CuO Cu nanocubes/MWCTs/GCE CuO nanoplatelets Cu/PANI/rGO/GCE Pt/PANI/rGO/CuO
Sensitivity (μA·mM−1·cm−2)
Linear range (mM)
Detection limit (μM)
Reference
1101 1359 1360 1211 1066 1096 3490 603 1252
0–0.6 0.28–4.6 0.002–4.0 0.04–5.0 0.1–2.4 0–7.5 0–0.8 0.01–9.66 0–13
25 0.24 0.7 4 2 1 0.5 1.34 1.5
[46] [13] [15] [12] [47] [48] [49] [33] This work
prepared Pt/PANI/rGO/CuO electrodes is about 8.15%, indicating a good reproducibility of the Pt/PANI/rGO/CuO electrodes. To investigate the sensor selectivity, the response of the Pt/PANI/ rGO/CuO electrode was examined in the presence of some common interfering species such as L-ascorbic acid (AA), acetaminophen (AP) and uric acid (UA). As the concentration of glucose in the human blood serum is about 30 times of AA, UA and AP [51], the selectivity performance of the sensor was studied by measuring the amperometric responses of Pt/PANI/rGO/CuO electrodes at the constant potential of 0.6 V towards stepwise additions of 1 mM glucose (three times), 0.11 mM AA, 0.17 mM AP, 0.48 mM UA and 1 mM glucose (three times) into 0.1 M NaOH solution. The sensor responses of these interferons relative to 1 mM glucose are 5.3% (AA), 8% (AP) and 7.6% (UA), respectively as shown in Fig. 7(B). As the results indicated, the responses of the proposed electrode to these interfering species were obviously much less compared to response to glucose. The stability of Pt/PANI/rGO/CuO electrodes was also investigated. The stability was detected by measuring the current response to 0–20 mM mM glucose before and after the electrodes having been stored under ambient conditions for 15 days. As Fig. 7(C) shows, the electrode retained 89.5% of its initial sensitivity after a 15 days storage and the stability during this period was acceptable. In order to evaluate the practical application of the prepared sensor, the Pt/PANI/rGO/CuO electrodes were tested in bovine serum samples. The bovine serum sample was firstly diluted with 0.1 M NaOH and the glucose concentrations of the bovine serum samples were adjusted by adding 1 M glucose solution into the samples. The glucose concentration changes of the samples were determined by a lab accurate glucose and lactate analyzer. All the measurements were carried out four times and the results are listed in Table 1. The results measured by the prepared glucose sensor agree well with the analyzer results. The calculated RSD and recovery show good consistency and repeatability of the sensors. Thus, the proposed glucose sensor could potentially be used to determine the glucose concentration in real blood serum. Table 2 compares the performances of this proposed Pt/PANI/rGO/ CuO electrode with some recent reported non-enzymatic glucose sensors based on Cu and CuO nanomaterials. As shown in this table, the Pt/ PANI/rGO/CuO electrode performance is comparable with these reported electrodes. Remarkably, the electrode prepared in this paper has a much wider linear range with the same sensitivity. Therefore, according to its high sensitivity, wide testing range and good stability, the proposed electrode can be a promising candidate for glucose detection.
SEM and the electrochemical response of the proposed electrodes in presence of glucose was investigated in 0.1 M NaOH. The proposed sensors exhibit a series of excellent sensing properties of good sensitivity, wide linear range, low detection limit and fast response time. These good properties may attribute to the fast electron transfer efficiency of rGO. Furthermore, the sensors can effectively resist the effect of interferences such as UA, DA, AA and the electrode showed ~90% of its initial signal after 15 days. These advantages and its good performances (especially its high sensitivity and wide linear range) make the proposed Pt/PANI/rGO/CuO electrode a promising candidate for glucose detection. Acknowledgment This work was financially supported by the National Natural Science Foundation of China (No. 81501555, No. 61501400) and Natural Science Foundation of Zhejiang Province (No. LY18H180006). References [1] Z. Chu, L. Shi, L. Liu, Y. Liu, W. Jin, Highly enhanced performance of glucose biosensor via in situ growth of oriented Au micro-cypress, J. Mater. Chem. 22 (2012) 21917–21922. [2] T.H. Le, G.S. Kang, S.H. Hur, Highly sensitive non-enzymatic glucose sensor based on Pt nanoparticle decorated graphene oxide hydrogel, Sensors Actuators B Chem. 210 (2015) 618–623. [3] B. Haghighi, B. Karimi, M. Tavahodi, H. Behzadneia, Fabrication of a nonenzymatic glucose sensor using Pd-nanoparticles decorated ionic liquid derived fibrillated mesoporous carbon, Mater. Sci. Eng. C 52 (2015) 219–224. [4] J.S. Ye, B.D. Hong, Y.S. Wu, H.R. Chen, C.L. Lee, Heterostructured palladium-platinum core-shell nanocubes for use in a nonenzymatic amperometric glucose sensor, Microchim. Acta 183 (2016) 3311–3320. [5] H. Li, C.Y. Guo, C.L. Xu, A highly sensitive non-enzymatic glucose sensor based on bimetallic Cu-Ag superstructures, Biosens. Bioelectron. 63 (2015) 339–346. [6] C. Shen, J. Su, X. Li, J. Luo, M. Yang, Electrochemical sensing platform based on Pd–Au bimetallic cluster for non-enzymatic detection of glucose, Sensors Actuators B Chem. 209 (2015) 695–700. [7] H. Liu, X. Wu, B. Yang, Z. Li, L. Lei, X. Zhang, Three-dimensional porous NiO nanosheets vertically grown on graphite disks for enhanced performance non-enzymatic glucose sensor, Electrochim. Acta 174 (2015) 745–752. [8] K. Khun, Z.H. Ibupoto, X. Liu, V. Beni, M. Willander, The ethylene glycol template assisted hydrothermal synthesis of Co3O4, nanowires; structural characterization and their application as glucose non-enzymatic sensor, Mater. Sci. Eng. 194 (2015). [9] J. Zhang, J. Ma, S. Zhang, W. Wang, Z. Chen, A highly sensitive nonenzymatic glucose sensor based on CuO nanoparticles decorated carbon spheres, Sensors Actuators B Chem. 211 (2015) 385–391. [10] E. Reitz, W. Jia, M. Gentile, Y. Wang, Y. Lei, CuO nanospheres based nonenzymatic glucose sensor, Electroanalysis 20 (2008) 2482–2486. [11] L.-C. Jiang, W.-D. Zhang, A highly sensitive nonenzymatic glucose sensor based on CuO nanoparticles-modified carbon nanotube electrode, Biosens. Bioelectron. 25 (2010) 1402–1407. [12] X.W. Liu, P. Pan, Z.M. Zhang, F. Guo, Z.C. Yang, J. Wei, Z. Wei, Ordered self-assembly of screen-printed flower-like CuO and CuO/MWCNTs modified graphite electrodes and applications in non-enzymatic glucose sensor, J. Electroanal. Chem. 763 (2016) 37–44. [13] A. Esmaeeli, A. Ghaffarinejad, A. Zahedi, O. Vahidi, Copper oxide-polyaniline nanofiber modified fluorine doped tin oxide (FTO) electrode as non-enzymatic glucose sensor, Sensors Actuators B Chem. 266 (2018) 294–301. [14] P.M. Nia, W.P. Meng, F. Lorestani, M.R. Mahmoudian, Y. Alias, Electrodeposition of copper oxide/polypyrrole/reduced graphene oxide as a nonenzymatic glucose biosensor, Sensors Actuators B Chem. 209 (2015) 100–108.
4. Conclusion A non-enzymatic glucose sensor based on Pt/PANI/rGO/CuO electrode was fabricated and studied in this paper. PANI/GO composite nanostructure was prepared by a simple electro-polymerization and deposition process in aniline and graphene oxide mixture solution. After GO was reduced, CuO nanoparticles were electrodeposited on Pt/ PANI/rGO layer. The morphology and structure were characterized by 8
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[15] L. Luo, L. Zhu, Z. Wang, Nonenzymatic amperometric determination of glucose by CuO nanocubes-graphene nanocomposite modified electrode, Bioelectrochemistry 88 (2012) 156–163. [16] N.K. Guimard, N. Gomez, C.E. Schmidt, Conducting polymers in biomedical engineering, Prog. Polym. Sci. 32 (2007) 876–921. [17] M. Xu, Y. Song, Y. Ye, C. Gong, Y. Shen, L. Wang, L. Wang, A novel flexible electrochemical glucose sensor based on gold nanoparticles/polyaniline arrays/carbon cloth electrode, Sensors Actuators B Chem. 252 (2017). [18] K. Ghanbari, Z. Babaei, Fabrication and characterization of non-enzymatic glucose sensor based on ternary NiO/CuO/polyaniline nanocomposite, Anal. Biochem. 498 (2016) 37–46. [19] D. Zhai, B. Liu, Y. Shi, L. Pan, Y. Wang, W. Li, R. Zhang, G. Yu, A highly sensitive glucose sensor based on Pt nanoparticle/polyaniline hydrogel heterostructures, ACS Nano 7 (2013) 3540–3546. [20] Z. Yu, H. Li, X. Zhang, N. Liu, W. Tan, X. Zhang, L. Zhang, Facile synthesis of NiCo2O4@polyaniline core-shell nanocomposite for sensitive determination of glucose, Biosens. Bioelectron. 75 (2016) 161–165. [21] L.V. Lukachova, E.A. Shkerin, E.A. Puganova, E.E. Karyakina, S.G. Kiseleva, A.V. Orlov, G.P. Karpacheva, A.A. Karyakin, Electroactivity of chemically synthesized polyaniline in neutral and alkaline aqueous solutions: role of self-doping and external doping, J. Electroanal. Chem. 544 (2003) 59–63. [22] R.L. Razalli, M.M. Abdi, P.M. Tahir, A. Moradbak, Y. Sulaiman, L.Y. Heng, Polyaniline-modified nanocellulose prepared from Semantan bamboo by chemical polymerization: preparation and characterization, RSC Adv. 7 (2017) 25191–25198. [23] L. Huang, X. Li, Y. Ren, X. Wang, In-situ modified carbon cloth with polyaniline/ graphene as anode to enhance performance of microbial fuel cell, Int. J. Hydrog. Energy 41 (2016) 11369–11379. [24] E.A.D.O. Farias, S.S. Nogueira, A.M.D.O. Farias, M.S.D. Oliveira, M.D.F.C. Soares, H.N.D. Cunha, J.R.D.S. Junior, D.A.D. Silva, P. Eaton, C. Eiras, A thin PANI and carrageenan–gold nanoparticle film on a flexible gold electrode as a conductive and low-cost platform for sensing in a physiological environment, J. Mater. Sci. 52 (2017) 13365–13377. [25] W. Zheng, L. Hu, L.Y.S. Lee, K.Y. Wong, Copper nanoparticles/polyaniline/graphene composite as a highly sensitive electrochemical glucose sensor, J. Electroanal. Chem. 781 (2016) 155–160. [26] J. Narang, N. Chauhan, C.S. Pundir, A non-enzymatic sensor for hydrogen peroxide based on polyaniline, multiwalled carbon nanotubes and gold nanoparticles modified au electrode, Analyst 136 (2011) 4460–4466. [27] B. Zhang, Y. He, B. Liu, D. Tang, Nickel-functionalized reduced graphene oxide with polyaniline for non-enzymatic glucose sensing, Microchim. Acta 182 (2015) 625–631. [28] K. Ghanbari, F. Ahmadi, NiO hedgehog-like nanostructures/Au/polyaniline nanofibers/reduced graphene oxide nanocomposite with electrocatalytic activity for non-enzymatic detection of glucose, Anal. Biochem. 518 (2016) 143–153. [29] C. Lee, X. Wei, J.W. Kysar, J. Hone, Measurement of the elastic properties and intrinsic strength of monolayer graphene, Science 321 (2008) 385–388. [30] X. Lu, Y. Ye, Y. Xie, Y. Song, S. Chen, P. Li, L. Chen, L. Wang, Copper coralloid granule/polyaniline/reduced graphene oxide nanocomposites for nonenzymatic glucose detection, Anal. Methods 6 (2014) 4643–4651. [31] J. Luo, S. Jiang, H. Zhang, J. Jiang, X. Liu, A novel non-enzymatic glucose sensor based on Cu nanoparticle modified graphene sheets electrode, Anal. Chim. Acta 709 (2012) 47–53. [32] L. Jiang, Z. Fan, Design of advanced porous graphene materials: from graphene nanomesh to 3D architectures, Nanoscale 6 (2014) 1922–1945. [33] W. Chen, S. Li, C. Chen, L. Yan, Self-assembly and embedding of nanoparticles by in situ reduced graphene for preparation of a 3D graphene/nanoparticle aerogel, Adv. Mater. 23 (2011) 5679–5683.
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Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem
3D porous structured polyaniline/reduced graphene oxide/copper oxide decorated electrode for high performance nonenzymatic glucose detection Lu Fanga, Qin Zhub, Yu Caib, Bo Liangb, Xuesong Yeb, a b
T
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College of Life Information Science and Instrument Engineering, HangZhou DianZi University, Hangzhou, China Biosensor National Special Laboratory, College of Biomedical Engineering & Instrument Science, ZheJiang University, Hangzhou, China
ARTICLE INFO
ABSTRACT
Keywords: Non-enzymatic sensor Copper oxide Polyaniline nanofibers Reduced graphene oxide Glucose sensor
In this study, graphene oxide (GO) was directly co-deposited with polyaniline (PANI) on a Pt electrode and a 3D cluster structure of GO with wrinkled and rough surface was formed during the electro-polymerization and deposition process. Results of Raman spectra, X-ray photoelectron spectroscopy (XPS) showed that strong conjugated interactions had formed between GO clusters and PANI nanofibers. After GO was reduced, XPS measurements and electrochemical impedance spectra (EIS) studies indicated that most of the oxygen functional groups in GO were successfully removed and the conductivity of the composite material was dramatically increased. The morphology and structure of the prepared Pt/PANI/rGO/CuO electrodes were characterized by scanning electron microscopy (SEM) and the electrochemical response of the proposed electrodes in presence of glucose was investigated. Results showed that the 3D structure of rGO clusters greatly increased its effective surface area and improved the electronic transmission efficiency of the composite nanomaterial thus the Pt/ PANI/rGO/CuO modified electrodes displayed much higher electrocatalytic activity than the Pt/PANI/CuO modified electrodes towards glucose, exhibiting a high sensitivity of 1252 μA mM−1 cm−2, a fast response time of < 3 s, a low detection limit of 1.5 μM (S/N = 3) and a wide linear range from 0 mM to 13 mM. The Pt/PANI/ rGO/CuO electrode effectively resisted the effect of interferences such as L-ascorbic acid (AA), acetaminophen (AP) and uric acid (UA) and retained ~ 90% of its initial sensitivity after 15 days.
1. Introduction Over the past few years, various nanostructured metals (e.g., Au [1], Pt [2], Pd [3]), metal alloys (e.g., PtePd [4], CueAg [5], PteAu [6]) and metal oxide (e.g., NiO [7], Co3O4 [8], CuO [9]) have been used to fabricate nonenzymatic glucose sensors due to their excellent catalytic performance. Among these catalysts, CuO nanoparticles (CuONPs) have attracted much attention because of their advantages such as nontoxicity, low cost, simple fabrication technique and good electrochemical activity [10,11]. To enhance the electrocatalytic properties of CuO, a common used method is incorporating conductive materials such as carbon nanotubes (CNTs) [12], conductive polymers (e.g., polyaniline (PANI) [13], polypyrrole [14]) and graphene [15] with CuO to form composite materials. PANI is one of the most widely used conductive polymers in biosensors due to its good conductive property, high stability and ease preparation method [16]. Several composite materials such as metal or metal oxide decorated on PANI arrays have been reported to have high sensitivity to glucose. It has been reported that Au nanoparticles
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deposited on PANI arrays/carbon cloth integrated flexible electrode possessed the ability to electrochemically catalyze the oxidation of glucose and had a good accuracy for real serum samples analysis [17]. NiO/CuO composite nanoparticles [18], PtNPs [19] and NiCo2O4 [20] modified PANI nanofibers also showed similar high sensitivity towards glucose oxidation. Although PANI holds a special position among the conducting polymers and has been widely used in biochemical sensors, its electroactivity can only be retained in acidic media (usually at pH < 3) and tend to lose its conductivity due to deprotonation in neutral or alkaline solution [21–24], limiting its application in alkaline solution in which most of the nonenzymatic glucose sensors are tested. To overcome this limitation, some nanomaterials capable of increasing its conductivity have been combined with PANI to improve its electroactivity in alkaline solution, such as graphene [25], multiwalled carbon nanotubes [26] and graphene oxide (GO) [27,28]. Graphene, a kind of carbonaceous material with good conductivity, large specific surface area and stable chemical properties [29], has also been extensively applied in glucose electrode modification. In many biochemical sensors' applications, graphene, graphene oxide (GO) and
Corresponding author. E-mail addresses: [email protected] (B. Liang), [email protected] (X. Ye).
https://doi.org/10.1016/j.jelechem.2019.04.032 Received 2 January 2019; Received in revised form 20 March 2019; Accepted 9 April 2019 Available online 10 April 2019 1572-6657/ © 2019 Published by Elsevier B.V.
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Scheme 1. Procedure for the fabrication of the Pt/PANI/rGO/CuO electrode.
Fig. 1. SEM micrographs of the surface appearance of the electrodes. (A) Pt/PANI layer, (B) Pt/PANI/CuO layer, (C) Pt/PANI/GO layer, (D) enlarged view of Pt/ PANI/GO layer, (E) Pt/PANI/rGO/CuO layer, (F) EDX spectrum of Pt/PANI/rGO/CuO layer.
reduced graphene oxide (rGO) are decorated on the surface of sensors with a planer 2D structure and improve the sensor's performance [25,30,31]. However, the planer 2D structure and easy-to-aggregate properties of graphene and its derivatives greatly reduce their accessible surface area and active catalytic sites, thereby block their use in practical applications [32–34]. In this study, GO was co-deposited with PANI on the electrode and
formed a 3D cluster structure with wrinkled and rough surface during the electro-polymerization and deposition process. The 3D structure of GO clusters increased its effective surface area and thus improved the electronic transmission efficiency of the composite nanomaterial. After GO was reduced, Cu nanoparticles were deposited on the PANI/rGO layer and oxidized into CuO subsequently, then a non-enzymatic electrochemical glucose biosensor was finally constructed. The interaction 2
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biosensor exhibited substantial electrocatalytic activity towards glucose, and showed an excellent analytical performance with the sensitivity of 1252 μA mM−1 cm−2 and wide linear range from 0 mM to 13 mM towards glucose. These high performances made it a promising application candidate in nonenzymatic glucose detection. 2. Experimental 2.1. Materials Platinum electrode was purchased from Chinstrument Co., Ltd. (Shanghai, China). Aqueous solution of graphene oxide (Lateral Dimension: 50–200 nm, Concentration: 2 mg/ml) was purchased from Nanjing XFNANO Materials Tech. Co. Ltd. (Nanjing, China). Copper (II) nitrate hexahydrate (Cu(NO3)2·6 H2O), potassium nitrate (KNO3), sodium hydroxide (NaOH) and hydrochloric acid (HCl) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Chloroplatinic acid, Ascorbic acid (AA), acetaminophen (DA), and uric acid (UA) were purchased from Sigma-Aldrich Co., LLC. (Shanghai, China). All reagents were of analytical grade and all aqueous solutions were prepared with deionized (DI) water. Counter electrode (Pt electrode) and Reference electrode (KCl solution saturated Ag/AgCl electrode) were bought from Shanghai Chenhua Instrument Company (Shanghai Chenhua Co., China).
Fig. 2. Raman spectra of Pt/PANI, Pt/PANI/GO, Pt/PANI/rGO and Pt/PANI/ rGO/CuO layers.
between nanomaterials, the morphologies and electrochemical activities such as sensitivity, linearity, selectivity, repeatability and stability of the prepared Pt/PANI/rGO/CuO glucose sensor were tested. This
Fig. 3. (A) XPS spectra of Pt/PANI, Pt/PANI/GO and Pt/PANI/rGO, (B) C 1s XPS spectra of Pt/PANI, (C) C 1s XPS spectra of Pt/PANI/GO, (D) C 1s XPS spectra of Pt/ PANI/rGO. 3
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Fig. 4. (A) CVs for different electrodes in 0.1 M NaOH without glucose, (B) CVs for different electrodes in 0.1 M NaOH with 4 mM glucose, (C) Reduction CV curves of Pt/PANI/GO electrode in 1 M NaOH, (D) The electrochemical impedance spectra of Pt, Pt/PANI, Pt/PANI/GO, Pt/PANI/rGO and Pt/PANI/rGO/CuO electrodes in 0.1 M NaOH solution over a frequency range of 0.01 to 100 kHz.
50 mV·s−1 for 10 cycles. After that, the Pt/PANI/GO electrodes were rinsed with DI water to wash away the residual hydrochloric acid. To increase the conductivity of the PANI/GO layer, the Pt/PANI/GO electrodes were reduced in an oxygen-free 1.0 M NaOH solution to transform GO into rGO. The electrochemical reduction process was performed by applying a scanning potential from −1.1 V to 0 V with a scan rate of 25 mV·s−1 for 8 cycles. CuO nanoparticles were deposited on the Pt/PANI/rGO electrodes surface by an electrochemical method. Firstly, 12 cycles of cyclic voltammetry between −0.7 to 0.8 V with a scan rate of 25 mV·s−1 were first applied to the Pt/PANI/rGO electrodes in 0.01 M Cu(NO3)2 and 0.1 M KNO3 solution for the formation of Cu nanoparticles on the surface of the electrodes. Subsequently, Cu nanoparticles were oxidized to the CuO by applying 14 cycles of cyclic voltammetry from 0 to 0.8 V (50 mV·s−1) in 0.05 M NaOH solution and then washed with DI water. After all these steps, the Pt/PANI/rGO/CuO electrodes had been prepared. Pt/PANI/CuO electrodes were prepared as a control group. The preparation of Pt/PANI/CuO electrodes was almost the same as the Pt/ PANI/rGO/CuO electrodes preparation process except that GO was not added in the first electropolymerization process and the Pt/PANI electrode did not to reduce in NaOH solution. After electropolymerization of PANI, electro-deposition of Cu nanoparticles and Cu oxidation, the Pt/PANI//CuO electrodes had been prepared.
2.2. Apparatus All electrochemical measurements were performed using an electrochemical workstation (μAutolab III, Metrohm, Switzerland) at the room temperature. Glucose concentration changes in the bovine serum samples were measured by a lab accurate glucose and lactate analyzer (Biosen C-Line, EKF, Germany). Scanning electron microscopic (SEM) images and Energy Dispersive X-Ray Spectroscopy (EDX) were collected on a field emission scanning electron microscope (SEM, SIRION FEI, Netherlands). Raman spectra were collected using a laser confocal Raman spectrometer (Horiba Jobin Yvon, LabRAM HR Evolution) with a 532 nm HeeNe laser. X-ray photoelectron spectroscopy (XPS) measurements were performed sing a Thermo Scientific ESCALAB 250Xi spectrometer with a monochromated Al Ka radiation (hv = 1486.6 eV). 2.3. Preparation of the sensor The nonenzymatic glucose sensor was prepared with the process as shown in Scheme 1. Pt electrodes were carefully polished and washed by DI water and ethanol, respectively. Then, the Pt electrodes were dipped in a 1.0 M hydrochloric acid solution containing 0.5 M aniline (Ani) and 0.5 mg/ml GO for electropolymerization of PANI/GO. The PANI/GO electropolymerization was carried out by cyclic voltammetry in the potential window of −0.1 to 1.2 V with the scan rate of 4
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Fig. 5. (A) CVs of the Pt/PANI/rGO/CuO modified electrodes from 0 V to 0.9 V in 0.1 M of NaOH solution at different scan rates, (B) CVs of Pt/PANI/rGO/CuO electrode from −0.5 V to 0.9 V in 0.1 M NaOH solution with various concentrations of glucose, (C) Schematic illustration of the glucose electrocatalytic reaction mechanism on the surface of Pt/PANI/rGO/CuO electrode.
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2.4. Characterization All the electrochemical procedures in this study was performed using a classic three-electrode system including a platinum electrode as the counter electrode, an Ag/AgCl electrode as the reference electrode and a modified platinum electrode as the working electrode. 0.1 M NaOH solution was employed as the supporting electrolyte in the analytical procedure. Electrochemical behaviors of Pt/PANI/rGO/CuO electrode were investigated by cyclic voltammetry in the potential window of −0.5 V to 0.9 V. Electrochemical impedance spectra (EIS) of Pt/PANI, Pt/PANI/GO, Pt/PANI/rGO modified electrodes was measured over a frequency range of 0.01 to 100 KHz. Amperometric detection of glucose was performed under the potential of 0.6 V and continues adding 1 M glucose solution to the supporting electrolyte every 30 s after it reached stable current. 3. Results and discussion 3.1. Morphology and structure of electrode SEM was used to characterize the morphologies of the Pt/PANI, Pt/ PANI/CuO, Pt/PANI/GO and Pt/PANI/rGO/CuO electrode layers. Fig. 1(A) shows the surface appearance of PANI nanofibers. The diameter of the PANI nanofibers is around 100 nm and the length of the nanofibers is about 1 um. The PANI nanofibers represent a well-arranged polymer chain structure with high ratio of surface-to-volume, that is useful for the decorating of CuO particles. Fig. 1(B) shows the surface morphology of the Pt/PANI/CuO layer. As can be seen, the CuO cubic nanoparticles with a uniform size ranged about 500 nm are evenly dispersed on the surface of PANI nanofibers and embedded between them. Fig. 1(C) shows the surface morphology of Pt/PANI/GO layer. As can be seen, the GO clusters, which are uniformly embedded in the PANI nanofibers matrix during the co-deposition process, form a 3D structure with wrinkled surface. Fig. 1(D) shows an enlarged view of Pt/PANI/GO layer, we can see the GO surface covered by short PANI nanofibers. The 3D structure of GO clusters increases its effective surface area compared to the 2D structure. Fig. 1(E) shows the morphology of Pt/PANI/rGO/CuO layer after Cu was deposited and oxidized. The CuO nanoparticles are uniformly dispersed on the surface of rGO clusters and PANI nanofibers. Fig. 1(F) gives the SEM/EDX spectrum of Pt/PANI/rGO/CuO layer. The Au peak comes from the gold sputtering procedure in sample surface processing before SEM. We can confirm from the EDX spectrum that CuO nanoparticles have been deposited on the electrode surface. Raman analysis was performed to study the specific interaction between GO and the PANI nanofibers. Raman spectra of the Pt/PANI layer, Pt/PANI/GO layer and Pt/PANI/rGO/CuO layer are plotted in Fig. 2. Several typical PANI characteristic peaks were observed in the Pt/PANI layer, including 1161 cm−1 (CeH bending vibration of the quinoid rings) [35], 1213 cm−1 (CeH bending vibration of the benzenoid rings), 1485 cm−1 (the stretching vibrations of C]N groups) [36], 1582 cm−1 (C]C stretching of the benzenoid rings) [37,38]. After GO was co-deposited with PANI, a D band peak around 1348 cm−1, which is known as defective band that usually arises from the first order scattering of sp3 hybridized carbon atoms [39], appears in the PANI/GO Raman spectrum. Furthermore, the relatively increase of G band intensity also indicate an increase of stretching vibration of sp2 hybridized C]C bonds [39], which may come from the C]C stretching vibration of graphene. The appearance of D band and increase of G band confirm the existence of strong interactions between GO and the PANI. When GO was reduced, the relative D band intensity of the Pt/ PANI/rGO increased. The increase of ID/IG ratio value of Pt/PANI/rGO indicates the formation of disordered new graphitic domains during the reduction process, suggesting the successful reduction of GO. For Pt/ PANI/rGO/CuO, the decrease of ID/IG ratio may occur due to the repair of defects on rGO surface during the CuO decoration. 5
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Fig. 6. (A) Amperometric titration response of Pt/PANI/rGO/CuO electrode at various concentration of glucose in 0.1 M NaOH, (B) The calibration curve of Pt/ PANI/CuO and Pt/PANI/rGO/CuO electrodes of glucose (0 mM–20 mM) in 0.1 M NaOH.
The XPS spectra of Pt/PANI, Pt/PANI/GO and Pt/PANI/rGO are shown in Fig. 3. As can be seen from Fig. 3(A), among of these presented materials, peaks centered at 285 eV (C 1s), 400 eV (N 1 s) and 534 eV (O 1 s) are all observed from the wide range spectrum, and the N 1 s peak confirms the presence of PANI in the composites. Pure PANI has a small amount of O compared with the composites and after being co-deposited with GO, the O 1s peak intensity of Pt/PANI/GO significantly increases, confirming the combination of PANI and GO. The O 1s peak of Pt/PANI/rGO is much lower than that of Pt/PANI/GO, indicating that most of the oxygen functional groups on the surface of GO of PANI/GO have been eliminated during the reduction process. Fig. 3(B)–(D) shows the deconvoluted C 1s spectra of Pt/PANI, Pt/ PANI/GO and Pt/PANI/rGO, each of which can be curve-fitted into five peak components: CeC group at 284.5 eV [40], C]C group at 285.2 eV, CeN group at 285.9 eV, CeO group at 286.9 eV [41] and C] O group at 287.9 eV [42,43]. The areas of the five C 1s components of Pt/PANI/GO show that the oxygenated C (CeO and C]O components) is about 28% (284.5 eV), while that of PANI/rGO is 13%. These results indicate that most of the oxygen functional groups in GO were successfully removed and the conductivity of GO would be recovered [40,44].
consistent with other studies [45,46]. The GO reduction peak current shows a decreasing trend during the oxidoreduction process from the first cycle to the last cycle, indicating that the most of the oxygen functional groups such as epoxy, carbonyl and hydroxyl groups have been gradually reduced and rGO formed during this procedure. To study the electron transfer ability between electrolyte and the surface of different electrodes, the electrochemical impedance spectra (EIS) of Pt/PANI, Pt/PANI/GO, Pt/PANI/rGO and Pt/PANI/rGO/CuO electrodes were measured in 0.1 M NaOH solution over a frequency range of 0.01 to 100 KHz (shown in Fig. 4(D)). Sodium hydroxide solution was chosen as the electrolyte solution because the conductivity of PANI is very sensitive to the pH of electrolyte solution and the nonenzymatic glucose sensor was finally tested in the alkaline solution. In order to compare the electron transfer capacity of the composite material with and without 3D structured rGO, the electron transfer resistances (RCT) of them were investigated by EIS. As shown Fig. 4(D), the Pt electrode has the most minimum impedance because of the good conductivity of platinum. The Rct of Pt/ PANI/GO electrode (6702 Ω) is smaller than that of Pt/PANI electrode (9772 Ω). As we know, the conductivity of PANI nanofibers could greatly decrease in alkaline solution [40,47], which would reduce the electron transfer efficiency of the electrode. The GO clusters dispersed in PANI nanofibers could reduce electron transfer resistance between CuO nanoparticles and electrode surface. However, the conductivity of Pt/PANI/GO electrode was still not desirable due to the oxygenous groups on the GO surface. After electrochemical reduction in alkaline solution, the Pt/PANI/rGO electrode showed a much smaller Rct (258 Ω) than Pt/PANI/GO electrode (6702 Ω), indicating that most of the oxygenous groups on the GO surface had been removed. The impedance of Pt/PANI/rGO/CuO electrode increased (1950 Ω) after CuO was decorated on the Pt/PANI/rGO surface because CuO is a p-type semiconductor which has poor conductivity [48]. Fig. 5(A) shows the CVs of the Pt/PANI/rGO/CuO modified electrodes from 0 V to 0.9 V in 0.1 M of NaOH solution at different scan rates separately. With the increasing sweep rates from 50 mV s−1 to 350 mV s−1, the oxidation peaks shift positively and the reduction peaks shift negatively. The calibration curve (the inset of Fig. 5A) exhibits that the oxidation peak currents increase linearly with the increasing scan rate with correlation coefficients (R2) of 0.992, indicating that the redox process is a typical surface controlled electrochemical process. Fig. 5(B) shows the CVs of Pt/PANI/rGO/CuO modified electrode from −0.5 V to 0.9 V in 0.1 M NaOH solution with various
3.2. Electrocatalytic performance of electrode Fig. 4(A) and (B) show the CVs for Pt/PANI, Pt/PANI/CuO, Pt/ PANI/GO, Pt/PANI/rGO, Pt/PANI/rGO/Cu and Pt/PANI/rGO/CuO electrodes in 0.1 M NaOH in both absence and presence of glucose (4 mM) with the scan rate of 50 mV·s−1 from −0.5 V to 0.9 V. Compare with the two CVs, we can see that Pt/PANI, Pt/PANI/CuO, Pt/PANI/GO and Pt/PANI/rGO electrodes have no oxidation peak in both absence and presence of glucose. After Cu nanoparticles were deposited and oxidized, the Pt/PANI/rGO/Cu and Pt/PANI/rGO/CuO electrodes show oxidation peaks to glucose at around 0.6 V, indicating that the Cu and CuO nanoparticles are the catalyzer of glucose in these nonenzymatic glucose sensors. Furthermore, the Pt/PANI/rGO/CuO electrode shows a higher oxidation current compared with Pt/PANI/rGO/Cu electrode. Therefore, we chose CuO nanoparticles as the catalyzer in this study. As reported by other studies, electrochemical method can equivalently, uniformly, firmly and steadily reduce graphene oxide to graphene [45]. In this study, the electrochemical reduction of GO was performed by applying −1.1 V to 0 V for eight cycles in 1 M NaOH. Fig. 4(C) shows typical reduction CV curves of Pt/PANI/GO electrode, the GO reduction peak is observed at around −0.9 V, which is 6
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Fig. 7. (A) Reproducibility of the Pt/PANI/rGO/CuO electrodes, (B)The chronoamperometric of glucose on Pt/PANI/rGO/CuO electrode in the presence of interfering species, (C) Stability of Pt/PANI/rGO/CuO electrodes stored under ambient conditions for 15 days.
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Table 1 Determination of glucose concentration in blood serum samples. Sample number 1 2 3 4 5 6
Added (mM) 2 4 6 8 10 12
Measured by our biosensor (mM) 2.01 4 5.89 7.92 9.67 11.15
Recovery (%)
RSD (%, n = 4)
100.5 100 98.17 99 96.7 92.92
3.51 4.23 4.28 3.86 3.92 3.91
concentrations of glucose (from 0 mM to 14 mM). The inset is a calibration curve corresponding to amperometric responses at 0.6 V, exhibiting a linear response up to 14 mM of glucose with correlation coefficients (R2) of 0.996. The electrooxidation of glucose involves the following steps as indicated in Fig. 5(C). First, the Cu(II) in forms of CuO is electrochemically oxidized to a strongly oxidizing Cu(III) in forms of CuOOH under the alkaline conditions during the potential scan [49,50] (Reaction 1). Once glucose is added, it is catalytically oxidized by the CuOOH and produces hydrolyzate gluconic acid as indicated in Reaction 2. The glucose oxidation peak is observed at around 0.6 V and this peak current increased with glucose concentration. 3.3. Amperometric response characteristics of the sensor The responses of Pt/PANI/CuO and Pt/PANI/rGO/CuO electrodes in 0.1 M NaOH in the presence of different glucose concentrations (from 10 μM to 20 mM) were investigated at a constant potential (0.6 V vs. Ag/AgCl at room temperature) while the supporting solution was stirring during the measurements. Fig. 6(A) shows a typical response curve of the Pt/PANI/rGO/CuO electrode and the Pt/PANI/CuO electrode during tests. The inset of Fig. 6(A) shows the response of the Pt/PANI/ rGO/CuO electrodes to low glucose concentrations. As can be seen, the Pt/PANI/rGO/CuO electrodes show much higher response to glucose variation than that of Pt/PANI/CuO electrodes. Moreover, the Pt/ PANI/rGO/CuO electrodes exhibit a much faster response (response time is < 3 s) than Pt/PANI/CuO electrodes (response time is around 10 s). Fig. 6(B) illustrates a plot of current density (mA·cm−2) and calibration curves vs. glucose concentration (mM) of Pt/PANI/CuO and Pt/ PANI/rGO/CuO electrodes. The sensitivity of the Pt/PANI/CuO sensor is 349 μA·mM−1·cm−2 and the linear range is between 0 mM to 14 mM (R2 > 0.994). The sensitivity of the Pt/PANI/rGO/CuO sensor is 1252 μA·mM−1·cm−2 with a glucose detection limit of 1.5 μM (S/ N = 3) and the linear range is between 0 mM to 13 mM (R2 > 0.994). The sensitivity of the Pt/PANI/rGO/CuO sensor is 3.6 times that of the Pt/PANI/CuO sensor which may be due to the higher electron transfer efficiency of the rGO clusters co-deposited in the PANI nanofibers. As we know, the conductivity of PANI nanofibers will greatly decrease in alkaline solution and this will reduce electron transfer efficiency of the nanomaterial. The rGO clusters, which was uniformly dispersed in PANI nanofibers and form a 3D structure during the co-deposition process, could reduce the electron transport resistance between CuO nanoparticles and the electrode surface, thereby increasing the sensitivity and linear range of the sensor. 3.4. Reproducibility, selectivity and stability of the Pt/PANI/rGO/CuO electrode To examine the reproducibility of the Pt/PANI/rGO/CuO electrodes, five electrodes were prepared under the same condition and their chronoamperometric responses to 0–20 mM glucose (with 2 mM glucose concentration increase every step) in 0.1 M NaOH were measured. As shown in Fig. 7(A), the relative standard deviation of the five 7
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Table 2 Compression of this work with some of resent reports for electrochemical glucose detection. Electrode material CuNPs/PRG/SCT CuO-PANI/FTO CuO/Graphene/GCE CuO/MWCNTs Nanoporous CuO Cu nanocubes/MWCTs/GCE CuO nanoplatelets Cu/PANI/rGO/GCE Pt/PANI/rGO/CuO
Sensitivity (μA·mM−1·cm−2)
Linear range (mM)
Detection limit (μM)
Reference
1101 1359 1360 1211 1066 1096 3490 603 1252
0–0.6 0.28–4.6 0.002–4.0 0.04–5.0 0.1–2.4 0–7.5 0–0.8 0.01–9.66 0–13
25 0.24 0.7 4 2 1 0.5 1.34 1.5
[46] [13] [15] [12] [47] [48] [49] [33] This work
prepared Pt/PANI/rGO/CuO electrodes is about 8.15%, indicating a good reproducibility of the Pt/PANI/rGO/CuO electrodes. To investigate the sensor selectivity, the response of the Pt/PANI/ rGO/CuO electrode was examined in the presence of some common interfering species such as L-ascorbic acid (AA), acetaminophen (AP) and uric acid (UA). As the concentration of glucose in the human blood serum is about 30 times of AA, UA and AP [51], the selectivity performance of the sensor was studied by measuring the amperometric responses of Pt/PANI/rGO/CuO electrodes at the constant potential of 0.6 V towards stepwise additions of 1 mM glucose (three times), 0.11 mM AA, 0.17 mM AP, 0.48 mM UA and 1 mM glucose (three times) into 0.1 M NaOH solution. The sensor responses of these interferons relative to 1 mM glucose are 5.3% (AA), 8% (AP) and 7.6% (UA), respectively as shown in Fig. 7(B). As the results indicated, the responses of the proposed electrode to these interfering species were obviously much less compared to response to glucose. The stability of Pt/PANI/rGO/CuO electrodes was also investigated. The stability was detected by measuring the current response to 0–20 mM mM glucose before and after the electrodes having been stored under ambient conditions for 15 days. As Fig. 7(C) shows, the electrode retained 89.5% of its initial sensitivity after a 15 days storage and the stability during this period was acceptable. In order to evaluate the practical application of the prepared sensor, the Pt/PANI/rGO/CuO electrodes were tested in bovine serum samples. The bovine serum sample was firstly diluted with 0.1 M NaOH and the glucose concentrations of the bovine serum samples were adjusted by adding 1 M glucose solution into the samples. The glucose concentration changes of the samples were determined by a lab accurate glucose and lactate analyzer. All the measurements were carried out four times and the results are listed in Table 1. The results measured by the prepared glucose sensor agree well with the analyzer results. The calculated RSD and recovery show good consistency and repeatability of the sensors. Thus, the proposed glucose sensor could potentially be used to determine the glucose concentration in real blood serum. Table 2 compares the performances of this proposed Pt/PANI/rGO/ CuO electrode with some recent reported non-enzymatic glucose sensors based on Cu and CuO nanomaterials. As shown in this table, the Pt/ PANI/rGO/CuO electrode performance is comparable with these reported electrodes. Remarkably, the electrode prepared in this paper has a much wider linear range with the same sensitivity. Therefore, according to its high sensitivity, wide testing range and good stability, the proposed electrode can be a promising candidate for glucose detection.
SEM and the electrochemical response of the proposed electrodes in presence of glucose was investigated in 0.1 M NaOH. The proposed sensors exhibit a series of excellent sensing properties of good sensitivity, wide linear range, low detection limit and fast response time. These good properties may attribute to the fast electron transfer efficiency of rGO. Furthermore, the sensors can effectively resist the effect of interferences such as UA, DA, AA and the electrode showed ~90% of its initial signal after 15 days. These advantages and its good performances (especially its high sensitivity and wide linear range) make the proposed Pt/PANI/rGO/CuO electrode a promising candidate for glucose detection. Acknowledgment This work was financially supported by the National Natural Science Foundation of China (No. 81501555, No. 61501400) and Natural Science Foundation of Zhejiang Province (No. LY18H180006). References [1] Z. Chu, L. Shi, L. Liu, Y. Liu, W. Jin, Highly enhanced performance of glucose biosensor via in situ growth of oriented Au micro-cypress, J. Mater. Chem. 22 (2012) 21917–21922. [2] T.H. Le, G.S. Kang, S.H. Hur, Highly sensitive non-enzymatic glucose sensor based on Pt nanoparticle decorated graphene oxide hydrogel, Sensors Actuators B Chem. 210 (2015) 618–623. [3] B. Haghighi, B. Karimi, M. Tavahodi, H. Behzadneia, Fabrication of a nonenzymatic glucose sensor using Pd-nanoparticles decorated ionic liquid derived fibrillated mesoporous carbon, Mater. Sci. Eng. C 52 (2015) 219–224. [4] J.S. Ye, B.D. Hong, Y.S. Wu, H.R. Chen, C.L. Lee, Heterostructured palladium-platinum core-shell nanocubes for use in a nonenzymatic amperometric glucose sensor, Microchim. Acta 183 (2016) 3311–3320. [5] H. Li, C.Y. Guo, C.L. Xu, A highly sensitive non-enzymatic glucose sensor based on bimetallic Cu-Ag superstructures, Biosens. Bioelectron. 63 (2015) 339–346. [6] C. Shen, J. Su, X. Li, J. Luo, M. Yang, Electrochemical sensing platform based on Pd–Au bimetallic cluster for non-enzymatic detection of glucose, Sensors Actuators B Chem. 209 (2015) 695–700. [7] H. Liu, X. Wu, B. Yang, Z. Li, L. Lei, X. Zhang, Three-dimensional porous NiO nanosheets vertically grown on graphite disks for enhanced performance non-enzymatic glucose sensor, Electrochim. Acta 174 (2015) 745–752. [8] K. Khun, Z.H. Ibupoto, X. Liu, V. Beni, M. Willander, The ethylene glycol template assisted hydrothermal synthesis of Co3O4, nanowires; structural characterization and their application as glucose non-enzymatic sensor, Mater. Sci. Eng. 194 (2015). [9] J. Zhang, J. Ma, S. Zhang, W. Wang, Z. Chen, A highly sensitive nonenzymatic glucose sensor based on CuO nanoparticles decorated carbon spheres, Sensors Actuators B Chem. 211 (2015) 385–391. [10] E. Reitz, W. Jia, M. Gentile, Y. Wang, Y. Lei, CuO nanospheres based nonenzymatic glucose sensor, Electroanalysis 20 (2008) 2482–2486. [11] L.-C. Jiang, W.-D. Zhang, A highly sensitive nonenzymatic glucose sensor based on CuO nanoparticles-modified carbon nanotube electrode, Biosens. Bioelectron. 25 (2010) 1402–1407. [12] X.W. Liu, P. Pan, Z.M. Zhang, F. Guo, Z.C. Yang, J. Wei, Z. Wei, Ordered self-assembly of screen-printed flower-like CuO and CuO/MWCNTs modified graphite electrodes and applications in non-enzymatic glucose sensor, J. Electroanal. Chem. 763 (2016) 37–44. [13] A. Esmaeeli, A. Ghaffarinejad, A. Zahedi, O. Vahidi, Copper oxide-polyaniline nanofiber modified fluorine doped tin oxide (FTO) electrode as non-enzymatic glucose sensor, Sensors Actuators B Chem. 266 (2018) 294–301. [14] P.M. Nia, W.P. Meng, F. Lorestani, M.R. Mahmoudian, Y. Alias, Electrodeposition of copper oxide/polypyrrole/reduced graphene oxide as a nonenzymatic glucose biosensor, Sensors Actuators B Chem. 209 (2015) 100–108.
4. Conclusion A non-enzymatic glucose sensor based on Pt/PANI/rGO/CuO electrode was fabricated and studied in this paper. PANI/GO composite nanostructure was prepared by a simple electro-polymerization and deposition process in aniline and graphene oxide mixture solution. After GO was reduced, CuO nanoparticles were electrodeposited on Pt/ PANI/rGO layer. The morphology and structure were characterized by 8
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