- Email: [email protected]
reduced graphene oxide as a nonenzymatic glucose biosensor
Accepted Manuscript Title: Electrodeposition of copper oxide/polypyrrole/reduced graphene oxide as a nonenzymatic glucose biosensor Author: Pooria Mn Woi Pei Meng Farnaz Lorestani M.R. Mahmoudian Y. Alias PII: DOI: Reference:
S0925-4005(14)01452-X http://dx.doi.org/doi:10.1016/j.snb.2014.11.072 SNB 17713
To appear in:
Sensors and Actuators B
Received date: Revised date: Accepted date:
22-9-2014 3-11-2014 12-11-2014
Please cite this article as: P. Mn, W.P. Meng, F. Lorestani, M.R. Mahmoudian, Y. Alias, Electrodeposition of copper oxide/polypyrrole/reduced graphene oxide as a nonenzymatic glucose biosensor, Sensors and Actuators B: Chemical (2014), http://dx.doi.org/10.1016/j.snb.2014.11.072 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Electrodeposition of copper oxide/polypyrrole/reduced graphene oxide as a
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nonenzymatic glucose biosensor
Pooria Mna,*, Woi Pei Menga, Farnaz Lorestania, MR Mahmoudianb, Y. Aliasa,*
Department of Chemistry, Shahid Sherafat, University of Farhangian, 15916 Tehran, Iran
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b
Department of Chemistry, University of Malaya, Kuala Lumpur 50603, Malaysia
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a
Email: [email protected]; [email protected]; [email protected];
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[email protected]; [email protected]
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*Authors to whom correspondence should be addressed; Email: [email protected];
Abstract report
the
synthesis
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We
te
d
[email protected]; Tel: +603-79676774; Fax: +603-79674188
and
application
of
copper
oxide/polypyrrole
nanofiber/reduced graphene oxide nanocomposite (CuxO/Ppy/rGO/GCE) for the detection of glucose (GLC). CuxO, Ppy and rGO were synthesized via electrodeposition process. The formation of the rGO and Ppy were approved by Fourier Transform Infrared Spectroscopy (FT-IR). Energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) confirmed the formation of copper oxide. The field emission scanning electron microscopy (FESEM) images depicted the existence of wrinkle rGO, Ppy nanofibers with diameter around 100 nm and the uniformity of the CuxO particles deposited on the Ppy nanofibers. Electrochemical impedance spectroscopy (EIS) data also indicated the charge transfer of each layer decreased compared to the underneath layer. By using cyclic voltammetry (CV) and
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chronoamperometry under pH 7.2, the electrocatalytic activity of CuxO/Ppy/rGO/GCE towards GLC was explored. The sensor presented a linear range of 0.1 to 100 mM (R2=0.991) of GLC, that is higher than most of the present nonenzymatic glucose biosensors based on
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CuxO, Ppy and rGO. The limit of detection (LOD) reaches 0.03 µM (at S/N=3). Additionally, the sensor exhibited remarkable reproducibility, stability and selectivity properties which
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make CuxO/Ppy/rGO/GCE a good nonenzymatic GLC sensor.
Keywords: Copper oxide; Polypyrrole; Reduced Graphene Oxide; Glucose; Nonenzymatic
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an
biosensor
1. Introduction
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More than 220 million of people around the world are suffering from diabetes which
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is a highly extensive disease bringing about metabolic disorders. Testing the blood glucose
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(GLC) is very crucial for diabetic patients and helps to evade the clustering of blood GLC (in the range of 4.4–6.6mM). Therefore it is of high significance to establish straightforward system with high sensitivity, selectivity and stability in order to distinguish GLC levels.[1-3] Graphite oxide was primarily recorded 150 years ago and reappeared tremendously in the studies due to the low cost and volume production of graphene-based materials. The layered structure of graphite oxide is similar to graphite’s structure but in graphite oxide, the sheet of carbon atoms is densely decorated by groups which contain oxygen, which besides increasing the interlayer distance, it makes the atomic-thick layers hydrophilic. Therefore, this is resulted to the exfoliation of oxidized layers in water under moderate ultra-sonication [4-9]. It also should be mentioned that the most interesting feature of GO is being partly reduced to
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graphene-like sheets through the removal of the groups which contain oxygen with the recovery of a conjugated structure [7, 8, 10-12]. In 1977 H.Shirakawa et al [13] reported electrical conductivity in a conjugated
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polymer and since then conducting polymers have been largely explored due to their unique electrical characteristics. Polypyrrole, among the conducting polymers is specifically
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advantageous for its different financial applications like chemical sensors [14, 15],
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supercapacitors [15-17], biosensors [2, 6, 7, 18, 19], gas sensors [20] and corrosion protection [21-23] because of being environmentally stable, electrically conductive and flexible.
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Recently a huge attempt has been made to expand polypyrrole nanostructures which exhibit unique physical and chemical characteristics preferable to their bulky counterpart and that is
technology [24-27].
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due to an expanding need for conducting polymers in the field of nano-science and Electrochemical polymerization provides a one-step procedure and
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offers precise control of the thickness and the structure of the resulting film [28].
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Transition metal oxides, like Cu2O are drawing a huge attention as sensors for
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detection of glucose because of their good characteristics such as low cost, ease of synthesis and post synthesis handling, stability, remarkable redox process at different potential ranges under several reaction conditions. Electrodes based on CuO or Cu2O (CuxO) showed a high electrocatalytic oxidation ability for GLC [29]. In the present paper, two different types of Ppy nanofibers, modified by CuxO (CuO
and Cu2O composite) nanoparticles were well prepared on reduced graphene oxide. Stability, sensitivity, reproducibility and high range of detection are the properties of the prepared biosensors which integrated the properties of rGO, Ppy and transition metal oxide.
2.
Experimental details
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2.1.
Materials All of the materials including D-(+)-glucose, potassium hydrogen phosphate (99%),
lithium perchlorate (99%), pyrrole (99.5%), potassium dihydrogen phosphate (99%) and
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copper(II) chloride dehydrate (99%) were purchased from Sigma–Aldrich and were used in
2.2.
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the form which they were received.
Instruments
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All the electrochemical measurement including electrochemical impedance
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spectroscopy (EIS), chronoamperometry and cyclic voltammetry (CV) were performed using a potentiostat/ galvanostat model PGSTAT-302N from the Autolab controlled by a USB
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IF030 (Metrohm Autolab) interface. A counter electrode, reference electrode and a working electrode formed a three-electrode compartment cell. SCE saturated KCl was the reference
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electrode for all the potentials. X-ray powder diffraction (XRD; Philips X’pert system using
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Cu Ka radiation), was used for characterizing the crystal phase. For morphologies comparison, the field emission scanning electron microscopy (FESEM) images were taken by
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exploiting FESEM, Quanta 200F. To perform Fourier Transform Infrared spectroscopy (FTIR) a spectrum 400 FT-IR/FT-FIR spectrometer was used.
2.3.
Preparation of the nonenzymatic GLC sensor
In order to fabricate the nonenzymatic biosensor, glassy carbon electrode was chosen
to act as the base electrode. By using alumina (under 1, 0.1 and 0.05 mm diameter) slurries in the pre-experiment preparations, the clean GCE was polished to a mirror and subsequently washed by water which was previously distilled twice and ultrasonicated in ethanol and distilled water for ten minutes respectively. To be ready for use, it was dried under high purity N2 gas flow.
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By exploiting a modified Hummers’ method, GO was synthesized [30]. The graphene oxide (GO) was deposited and reduced simultaneously on the glassy carbon surface via CV by scanning repetitively from 0 to -1.5 V vs SCE at scan rate of 1 mVs-1 in a solution
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composed of 7 mg L-1 graphene oxide and 0.1 M phosphate buffer (PBS) at pH 7.2. The electropolymerization of Ppy nanofibers on the surface of coated GCE with rGO
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was performed in two different methods:
First, by cyclic voltammetry in a single compartment cell, with the applied potential
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ranging from 0.0 to 0.8 V at a scan rate of 1 mV s−1, the electropolymerization was performed
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in 4 voltammetric cycles on the surface of rGO.
Second, amperometry was the method used for the electrodeposition of polypyrrole
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on the surface of rGO at the constant potential of 0.8 V for 800 s. The monomer solution for both methods contains mixed electrolytes in a 0.1 M phosphate
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buffer solution (pH 7.2), 0.1 M pyrrole monomer and 0.1 M LiClO4.
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Before oxidization by CV scan, in a solution containing 0.1 M KCl and four different concentrations of CuCl2 (10, 30, 60, 90 mM), the Cu nanoparticles were electrodeposited on
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the surface of modified electrode at the constant potential of -0.6 V. Right after this stage, in order to permit the Cu nanoparticles to enter the oxidation form (CuxO), CV was performed in 0.1 M NaOH solution at the applied range of -0.5 to 0.3 V at a scan rate of 50 mVs-1 for 40 cycles [1, 31].
To eliminate the O2, the electrolyte was purged before conducting the experiments for
10 min with highly purified N2 and after the experiments, the modified electrodes were washed for several times and dried with a flow of N2. Fig. 1 shows the process of the study schematically.
Fig. 1
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3.
Results and discussion
3.1.
Electrodeposition of rGO, Ppy and CuxO
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Fig. 2(a) shows the first cycle among the four cycles of the electrochemical deposition of rGO layer. As can be seen and also mentioned in the previous studies [32-34], one anodic
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and two cathodic peaks can be recognized. The electrochemical reduction of GO which is reversible is responsible for the cathodic current peak III. In contrast, the oxidation reduction
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pair of some electrochemically active oxygen-containing groups on graphene planes is
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responsible for anodic peak I and cathodic peak II. These active oxygen-containing groups cannot be eliminated by cyclic voltammetry method from the graphene sheets [35, 36]. The
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SEM image (Fig. 2(b)) confirms the formation of rGO film on GCE. The image of FESEM displays that the surface of GCE electrode with modified rGO is wrinkled and rough due to
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the formation of rGO. This can be justified as in the course of electrodeposition, when the
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electrode potential decreased to negative, GO was electrochemically reduced to form rGO which is extremely hydrophobic [37].
Ac ce p
The electropolymerization of Ppy nanofibers has been performed with two methods
with the same materials. Fig. 2(c) shows the first four successive cyclic voltammograms of the rGO/GCE. The process of monomer oxidation starts as the potential increases to 0.65 V vs. SCE, in the anodic scan of the first cycle on the surface of rGO/GCE with mixed electrolyte is composed of 0.1 M phosphate buffer solution, 0.1 M pyrrole monomers and 0.1 M LiClO4 at the scan rate of 1 mVs-1. The faster scan rate will lead to a shorter reaction time for each scan cycle and thus the increment of the film’s radius in a faster scan cycle is less than that of a slower scan cycle [26]. Fig. 2(d) shows the electropolymerization process with amperometry method. As can be seen, as electropolymerization process starts, a noticeable increase in the current is observed
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suggesting that a conductive polypyrrole has been formed and after around 50 s, the current reaches the steady state condition.
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Fig. 2
The FT-IR spectrum of the GO, rGO, Ppyamp and Ppyamp/rGO are shown in Fig. 3 (a,
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b, c, d), respectively. For GO, the broad peak centered at 3363 cm-1 is assigned to the O-H
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stretching vibrations while the peaks at 1740, 1630 and 1431 are attributed to C=O stretching, sp2-hybridized C=C group and O-H bending, C-OH stretching [38]. In addition, the peak at
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1050 cm-1 can be attributed to C-O vibration of epoxy or alkoxy groups. The peaks at 3299 and 3295 cm−1 in the Ppyamp and Ppyamp/rGO spectra (Fig. 3(c) and (d)) are attributed to N–H
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stretching vibrations of the pyrrole ring. The peak at 3361 cm−1 in the rGO spectra is related to O–H groups and the bands at 1753 and 1477 cm−1 are related to C-O and C-OH,
d
respectively (Fig. 3(b)). The peaks at 1260 and 1067 cm−1 in the rGO spectrum are
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recognized as the C-O stretching vibration of the epoxy and alkoxy groups, respectively [27].
Ac ce p
The peaks at 2938 and 2860 cm−1 in the rGO spectrum are related to the CH2 asymmetric and symmetric stretching vibrations, respectively. The peaks at 1703 and 1653 cm−1 are related to C-N-C bond in the Ppyamp and Ppyamp/rGO spectra in Fig. 3(c) and (d), respectively. The bands at 1570 and 1510 cm−1 are related to the C–C and C–N in the Ppyamp and Ppyamp/rGO spectra, respectively [39]. The peaks at 1471 and 1421 cm−1 are recognized as typical Ppy ring vibrations (Fig. 3(c) and (d)), respectively. The aliphatic C-H peaks (at 2866 and 2930 cm−1 in the Ppyamp/rGO spectrum) and the peaks representing the C-O stretching vibration of the epoxy (at 1270 and 1052 cm−1) and alkoxy groups (at 1268 and 1063 cm−1) in Ppyamp/rGO spectra, respectively, confirm the existence of rGO.
Fig. 3
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EDX analysis was employed to prove the elemental composition at various stages. Fig. 4(a) displays the EDX spectra of Ppyamp/rGO/GCE and CuxO/ Ppyamp/rGO/GCE.
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Elemental Cu is detected in CuxO/ Ppyamp/rGO/GCE, although it is not present in the unmodified Ppyamp/rGO/GCE. This supports the point that Cu was able to be successfully
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deposited onto Ppy nanofibers.
XRD analysis was employed to affirm the composition of CuxO electrodeposited on
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the surface of Ppy nanofibers. Fig. 4(b) presents the XRD patterns of the CuxO/Ppyamp/rGO.
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The diffraction peaks which have been obtained for CuxO/Ppyamp/rGO are in the same manner with the preceding recorded standards [40, 41]. No peak has been observed for Cu
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which shows that the Cu deposited on Ppy was fully changed into CuO and Cu2O composite
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[42].
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Fig. 4
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Fig. 5 displays the cyclic voltammetry of the bare GCE (inset), rGO/GCE (inset),
Ppyamp/rGO/GCE, Ppycv/rGO/GCE, in a 0.1 M phosphate buffer solution (pH = 7.2) and 1 mM concentration. Compared to the bare GCE, the rGO/GCE indicates a rise in the anodic and cathodic current. Mahmoudian [27] presented that the presence of rGO increases the conductivity of the system. The CVs of Ppycv/rGO/GCE and Ppyamp/GCE reveal a redox couple in the anodic and also cathodic scans. The doping/dedoping process of Ppy nanofibers is responsible for the peaks. When a positive potential is employed, the counter ions are occupied (doping) and later the anions make the positive charges of Ppy nanofibers balanced. In contrary, when a sufficient negative potential is used for the polymer, the counter ions are freed (de-doping). Fig. 5 (a (3, 4)) indicates the influence of the electropolymerization
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method on the electrocatalytic activity of the Ppy towards GLC oxidation. By comparing the CVs of Ppycv/rGO/GCE with Ppyamp/rGO/GCE, it will be approved that compared with CV method, synthesizing Ppy with amperometry shows much more sensitivity toward GLC.
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Fig. 5(b) displays the CVs of different concentrations of CuxO on the surface of Ppyamp/rGO/GCE in a 0.1 M phosphate buffer solution (pH = 7.2) and 1 mM glucose,
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scanned at applied potential ranged from -1 to 1 V at scan rate of 50 mVs-1. As can be seen,
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10 mM concentration of Cu is the best compared with the others. FESEM images (Fig. 6) also confirm the result.
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It is notable that during the electropolymerization, the overoxidation of Ppy may occur. Therefore the overoxidized Ppy can be reduced by the oxidation of GLC during their
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interaction.
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(1)
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Fig. 5
As can be seen in FESEM Fig. 6 (a, b), the surface morphologies of the amperometry
Ppy nanofibers matrix and cyclic voltammetry Ppy were characterized. Fig. 6(b) presents clear and comparatively smooth amperometry Ppy nanofibers in diameter of ~100 nm, more stretched than cyclic voltammetry Ppy. Fig. 6(a) shows that a larger surface area can be detected in amperometry method. The amperometry Ppy nanofibers have a well-arranged polymer chain structure with greatly high ratio of surface-to-volume that is useful for the decorating by CuxO particles. The FESEM of Ppycv (Fig. 6(a)) indicates that as a result of the variation of applied potential, the film formation is not homogenous. Besides, the existence of non-homogeneous polypyrrole confirms that the conditions of polymerization highly influence the morphology of the film [26]. The reason for homogeneity of Ppyamp is not
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similar to CV method. In CV method monomers meet a wider potential ranges which are not necessarily monomer oxidation, then polymers with various lengths are made and apparently they are not uniformed. While in amperometry method, monomers are exposed to oxidation
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potential very fast. The morphologies of the CuxO/Ppyamp/rGO/GCE composites with various
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concentrations of Cu nanoparticles are displayed in Fig. 6 (c, d, e, and f). It can be seen that 10 mM concentration of Cu is the best compared with the others in which CuxO particles are
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uniformly attached on the surface of Ppyamp nanofibers. These morphological features
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provide several beneficial properties, such as, more available active sites, high catalysis properties and large surface area of CuxO/Ppyamp/rGO/GCE for GLC oxidation. The FESEM
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also confirms that the agglomeration of CuxO took place with increasing the concentration of Cu nanoparticle.
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It should be mentioned that different scales were used to show how much
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agglomeration occurred in each concentration. As can be seen in Fig. 6 (b), the diameter of each fiber is almost 100 nm. Fig. 6(c) is also in the same scale and shows that the copper
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oxide particles uniformly covered each Ppy nanofiber. With increasing concentration (Fig. 6(d and e)), wider scales were chosen in order to show that the agglomerated particles were becoming bigger compared with Ppy nanofibers. In Fig. 6(f), all the copper oxide particles completely covered the surface so that there is no Ppy nanofiber to be distinguished.
Fig. 6
In order to analyze the impedance changes of the modified electrode, electrochemical impedance spectroscopy was employed. Fig. 7(A) depicts the Nyquist plots in 0.1 M KCl solution containing 1 mM Fe[(CN)6]3−/4− (1:1). The Nyquist plot of impedance spectra
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consists of semicircle portion which at higher frequencies correlates to the electron transfer limited process while on the other hands, a linear portion at lower frequencies correlates to the diffusion process. The electron transfer resistance (Rct), by using the diameter of the
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semicircle diameter can be evaluated. The results confirmed that the alteration of GCE by reduced graphene oxide makes
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the resistance of charge transfer extremely reduced which can be interpreted due to the fact that the rGO layer protects various small band gaps which are agreeable for the electron
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conduction [43]. Moreover, the comparison between the semicircle diameters from the
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Nyquist diagrams of CuxO/Ppyamp/rGO/GCE (1529 Ω), Ppyamp/rGO/GCE (429 Ω), Ppycv/rGO/GCE (2341 Ω) and rGO/GCE (19781 Ω) shows the direction of Rct:
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(Rct): GCE> rGO/GCE> Ppycv/rGO/GCE> CuxO/Ppyamp/rGO/GCE > Ppyamp/RGO/GCE The main reason for increasing the charge transfer in CuxO/Ppyamp/rGO/GCE
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conductivity [1, 44].
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compared with Ppyamp/RGO/GCE is that CuxO is a p-type semiconductor which has poor
In order to figure out the impedance parameters, the ZSimp Win software is
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employed in the simulations. The Rs(CPE[RctW)]) equivalent circuit model was employed in the simulation of the impedance behavior of all the modified electrodes, from the experimentally gained impedance data. By exploiting the series components, the model was developed. The first component is ohmic resistance of the solutions of the electrolyte Rs and the second one is a set of constant phase elements (CPE) and the resistance of layer which indicates the conductivity of the sample (Rct) that are in the parallel position. And additionally from the diffusion impedance, W for the Warburg element is a series connection to Rct.
Fig. 7
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Fig. 7(B) shows the Bode plot that is in agreement with results obtained from Nyquist
3.2.
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plot.
Optimization of the sensor
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In order to find the best potential, the relationship between the oxidation current of GLC and the applied potential was measured. To find proper potential for amperometric
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response, the applied potential of the CuxO/Ppyamp/rGO/GCE was evaluated over the range of -0.2 to 0.4 V. Finally +0.2 V was selected as the optimized potential. Fig. 8a indicates the
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amperometric responses at +0.2 V of CuxO/Ppyamp/rGO/GCE electrode with subsequently adding in GLC concentration from 0.1 to 100 mM. The comparable calibration curve is
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shown in Fig 8a (inset). The relationship between the current and the concentration which is linear, is settled in the concentration range from 0.1 to 100 mM (R2=0.996).
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The linear part increases from 0.1 mM to 100 mM (Fig 8a) with a linear regression
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equation of I = 141.21 (µA.mM−1) + 114.32 (R2= 0.9991). The following equations were used
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for calculating the limit of detection (LOD) and the limit of quantification (LOQ) of CuxO/Ppyamp/rGO/GCE:
(2) (3)
Where SB is the standard deviation of the blank solution and b is the slope of the calibration curve. The LOD and LOQ (S/N of 3) are estimated to be 0.03 µM and 0.11 µM for the linear part, respectively.
3.3.
Stability and reproducibility of CuxO/Ppyamp/rGO/GCE
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The studied sensor shows a good stability, with a loss of only 10.4% in current response after 2 weeks at 4 ◦C (Fig 8b). By measuring the response to 1 mM glucose over 1 month, the long term stability of sensor was studied. The sensor was kept in the atmosphere
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and for 10 first days, it was tested every day and the next 20 days, every 5 days. The results indicate that the response was relatively the same over the entire examination days,
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suggesting that the sensor can be used in long term applications.
It should be added that for five electrodes which have been made identically with a relative
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standard deviation (RSD) of 4.3% the reproducibility was explored, while 10 measurements
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for the same electrode were carried out by adding 1 mM GLC with RSD of 6.4%, showing
3.4.
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high repeatability.
Interference study
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Successive addition of 1 mM GLC, fructose, ascorbic acid, uric acid and lactose into
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0.1 M phosphate buffer solution (pH 7.2) was used for CuxO/Ppyamp/rGO/GCE in order to study the effect of common interfering species (Fig. 8b (inset)). As can be seen, the current of
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these interfering species does not reveal an obvious additional signal which indicates that this modified electrode has a good selectivity towards GLC. There is a comparison between the performance of the CuxO/Ppyamp/rGO/GCE and
those of previously reported nonenzymatic GLC sensors based on CuxO, Ppy and rGO in Table 1. The linear range of prepared sensor (0.1 –100 mM) is considerably greater than that of other CuxO, Ppy and rGO [1, 41, 44-48], making CuxO/Ppyamp/rGO/GCE high potential for industrialization. The high sensitive catalytic performance, the wide linear range and low detection limit can be attributed to the nature of CuxO based on Ppy nanofibers and moreover the existing rGO as a substrate for upper layer which increase the conductivity of the system. Comparing the CuxO modified electrode and CuO/Cu2O-modified electrode, it was found that
Page 13 of 30
due to the synergic effect of CuO and Cu2O (CuxO), the latter has a wider linear detection range towards electrocatalytic oxidation of GLC [49]. Furthermore, CuxO particles can finely cover the Ppy nanofibers and the CuxO can highly raise the electrocatalytic active areas and
GLC molecules to be detected, adequately enhanced electrons.
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Fig. 8
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enhance electron transfer. Additionally, the Ppy nanofibers can provide larger surface area for
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Table 1
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In order to find out the accuracy of the sensor, the sensor was applied to real blood serum samples for determination of GLC. By employing standard addition method, GLC in human
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blood was determined on the modified sensor. Before measuring the current response, 0.04 mL of the samples (contains 4.4-6.4 mM GLC) were diluted by 10 mL phosphate buffer solution
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(pH 7.2) and then GLC solutions were added one after another to the system. All the
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measurements were carried out five times and the results are listed in Table 2. The calculated
Ac ce p
recovery and relative standard deviation (RSD) values from Table 2 show that the prepared sensor possesses potential applications in determining certain concentration range of GLC.
4.
Table 2
Conclusion
CuxO/Ppy/rGO/GCE have been successfully prepared via an in-situ electrochemical
deposition process. XRD, FT-IR and EDX results confirmed the presence of CuxO, Ppy nanofibers and rGO. The FESEM images of the modified electrode revealed the existence of rGO, Ppy nanofibers and finally CuxO was formed uniformly and fully covered the nanofibers. The electrochemical behavior of GCE coated with the CuxO/Ppy/rGO/GCE film
Page 14 of 30
showed the highest electrocatalytic activity compared with other modified GCE. The impedance data confirmed that the charge transfer resistance (Rct) of the modified electrode was significant. CuxO/Ppy/rGO/GCE electrochemical sensor had a wide linear range up to
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100 mM GLC concentration, a high sensitivity and a low detection limit of 0.03 µM. These great performances including high selectivity and sensitivity, easy fabrication and especially
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wide linear range, make CuxO/Ppy/rGO/GCE an excellent amperometric sensor for
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determining glucose concentration.
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Acknowledgments
The researcher named Pooria Mn wishes to thank Mahtab Mahdavifar for precious This
research
is
supported
by
High
Impact
Research
MoE
Grant
M
reviews.
UM.C/625/1/HIR/MoE/SC/04 from the Ministry of Education Malaysia, UMRG Program
Ac ce p
te
d
RP012A-13SUS and University Malaya Centre for Ionic Liquids (UMCiL).
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te
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cr
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[1] F.H. Meng, W. Shi, Y.N. Sun, X. Zhu, G.S. Wu, C.Q. Ruan, et al., Nonenzymatic biosensor based on CuxO nanoparticles deposited on polypyrrole nanowires for improving detection range, Biosensors & Bioelectronics, 42(2013) 141-7. [2] B.D. Malhotra, A. Chaubey, S.P. Singh, Prospects of conducting polymers in biosensors, Anal Chim Acta, 578(2006) 59-74. [3] J. Wang, Electrochemical glucose biosensors, Chem Rev, 108(2008) 814-25. [4] H.D. Jang, S.K. Kim, H. Chang, J.W. Choi, J.X. Huang, Synthesis of graphene based noble metal composites for glucose biosensor, Mater Lett, 106(2013) 277-80. [5] T.K. Das, S. Prusty, Graphene-Based Polymer Composites and Their Applications, Polym-Plast Technol, 52(2013) 319-31. [6] S. Palanisamy, S.M. Chen, R. Sarawathi, A novel nonenzymatic hydrogen peroxide sensor based on reduced graphene oxide/ZnO composite modified electrode, Sensors and Actuators, B: Chemical, 166-167(2012) 372-7. [7] A.M. Golsheikh, N.M. Huang, H.N. Lim, R. Zakaria, C.Y. Yin, One-step electrodeposition synthesis of silver-nanoparticle-decorated graphene on indium-tinoxide for enzymeless hydrogen peroxide detection, Carbon, 62(2013) 405-12. [8] J. Ping, Y. Wang, J. Wu, Y. Ying, Development of an electrochemically reduced graphene oxide modified disposable bismuth film electrode and its application for stripping analysis of heavy metals in milk, Food Chem, 151(2014) 65-71. [9] R.K. Layek, A.K. Nandi, A review on synthesis and properties of polymer functionalized graphene, Polymer, 54(2013) 5087-103. [10] A.M. Haque, H. Park, D. Sung, S. Jon, S.Y. Choi, K. Kim, An electrochemically reduced graphene oxide-based electrochemical immunosensing platform for ultrasensitive antigen detection, Anal Chem, 84(2012) 1871-8. [11] S. Pei, H.-M. Cheng, The reduction of graphene oxide, Carbon, 50(2012) 3210-28. [12] D. Zhang, Y. Fang, Z. Miao, M. Ma, X. Du, S. Takahashi, et al., Direct electrodeposion of reduced graphene oxide and dendritic copper nanoclusters on glassy carbon electrode for electrochemical detection of nitrite, Electrochim Acta, 107(2013) 656-63. [13] H. Shirakawa, E.J. Louis, A.G. MacDiarmid, C.K. Chiang, A.J. Heeger, Synthesis of electrically conducting organic polymers: halogen derivatives of polyacetylene, (CH), J Chem Soc, Chem Commun, (1977) 578-80. [14] H. Qin, A. Kulkarni, H. Zhang, H. Kim, D. Jiang, T. Kim, Polypyrrole thin film fiber optic chemical sensor for detection of VOCs, Sensors and Actuators B: Chemical, 158(2011) 223-8. [15] V.J. Fulari, J.V. Thombare, A.B. Kadam, Chemical oxidative polymerization and characterization of polypyrrole thin films for supercapacitor application, Energy Efficient Technologies for Sustainability (ICEETS), 2013 International Conference on2013, pp. 1068-71. [16] Y. Zhao, J. Liu, Y. Hu, H. Cheng, C. Hu, C. Jiang, et al., Highly compression-tolerant supercapacitor based on polypyrrole-mediated graphene foam electrodes, Adv Mater, 25(2013) 591-5. [17] Y. Liu, Y. Zhang, G. Ma, Z. Wang, K. Liu, H. Liu, Ethylene glycol reduced graphene oxide/polypyrrole composite for supercapacitor, Electrochim Acta, 88(2013) 519-25. [18] P.K. Kathuroju, N. Jampana, Growth of Polypyrrole-Horseradish Peroxidase Microstructures for H2O2 Biosensor, Ieee T Instrum Meas, 61(2012) 2339-45.
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[19] N. German, J. Voronovic, A. Ramanavicius, A. Ramanaviciene, Gold nanoparticles and polypyrrole for glucose biosensor design, Procedia Engineer, 47(2012) 482-5. [20] Y. Mao, Q. Kong, B. Guo, X. Fang, X. Guo, L. Shen, et al., Polypyrrole-iron-oxygen coordination complex as high performance lithium storage material, Energy & Environmental Science, 4(2011) 3442-7. [21] R. Vera, R. Schrebler, P. Grez, H. Romero, The corrosion-inhibiting effect of polypyrrole films doped with p-toluene-sulfonate, benzene-sulfonate or dodecyl-sulfate anions, as coating on stainless steel in NaCl aqueous solutions, Prog Org Coat, 77(2014) 853-8. [22] Y. Lei, N. Sheng, A. Hyono, M. Ueda, T. Ohtsuka, Influence of pH on the synthesis and properties of polypyrrole on copper from phytic acid solution for corrosion protection, Prog Org Coat, 77(2014) 774-84. [23] M.B. González, S.B. Saidman, Electrodeposition of polypyrrole on 316L stainless steel for corrosion prevention, Corros Sci, 53(2011) 276-82. [24] J. Kopecka, D. Kopecky, M. Vrnata, P. Fitl, J. Stejskal, M. Trchova, et al., Polypyrrole nanotubes: mechanism of formation, Rsc Adv, 4(2014) 1551-8. [25] D.H. Nam, M.J. Kim, S.J. Lim, I.S. Song, H.S. Kwon, Single-step synthesis of polypyrrole nanowires by cathodic electropolymerization, J Mater Chem A, 1(2013) 8061-8. [26] M. Li, H. Zhu, X.H. Mao, W. Xiao, D.H. Wang, Electropolymerization of polypyrrole at the three-phase interline: Influence of polymerization conditions, Electrochim Acta, 92(2013) 108-16. [27] M.R. Mahmoudian, Y. Alias, W.J. Basirun, The electrical properties of a sandwich of electrodeposited polypyrrole nanofibers between two layers of reduced graphene oxide nanosheets, Electrochim Acta, 72(2012) 53-60. [28] Y.S. Lim, Y.P. Tan, H.N. Lim, W.T. Tan, M.A. Mahnaz, Z.A. Talib, et al., Polypyrrole/graphene composite films synthesized via potentiostatic deposition, J Appl Polym Sci, 128(2013) 224-9. [29] M. Lin, M. Cho, W.-S. Choe, J.-B. Yoo, Y. Lee, Polypyrrole nanowire modified with Gly-Gly-His tripeptide for electrochemical detection of copper ion, Biosens Bioelectron, 26(2010) 940-5. [30] H.N. Lim, N.M. Huang, S.S. Lim, I. Harrison, C.H. Chia, Fabrication and characterization of graphene hydrogel via hydrothermal approach as a scaffold for preliminary study of cell growth, International journal of nanomedicine, 6(2011) 181723. [31] W.-Z. Le, Y.-Q. Liu, Preparation of nano-copper oxide modified glassy carbon electrode by a novel film plating/potential cycling method and its characterization, Sensors and Actuators B: Chemical, 141(2009) 147-53. [32] H.L. Guo, X.F. Wang, Q.Y. Qian, F.B. Wang, X.H. Xia, A Green Approach to the Synthesis of Graphene Nanosheets, Acs Nano, 3(2009) 2653-9. [33] Y. Shao, J. Wang, M. Engelhard, C. Wang, Y. Lin, Facile and controllable electrochemical reduction of graphene oxide and its applications, J Mater Chem, 20(2010) 743. [34] M. Zhou, Y. Wang, Y. Zhai, J. Zhai, W. Ren, F. Wang, et al., Controlled Synthesis of Large-Area and Patterned Electrochemically Reduced Graphene Oxide Films, Chemistry – A European Journal, 15(2009) 6116-20. [35] L. Chen, Y. Tang, K. Wang, C. Liu, S. Luo, Direct electrodeposition of reduced graphene oxide on glassy carbon electrode and its electrochemical application, Electrochem Commun, 13(2011) 133-7.
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[36] C. Liu, K. Wang, S. Luo, Y. Tang, L. Chen, Direct electrodeposition of graphene enabling the one-step synthesis of graphene-metal nanocomposite films, Small, 7(2011) 1203-6. [37] S. Takahashi, N. Abiko, J.I. Anzai, Redox response of reduced graphene oxide-modified glassy carbon electrodes to hydrogen peroxide and hydrazine, Materials, 6(2013) 184050. [38] W.J. Basirun, M. Sookhakian, S. Baradaran, M.R. Mahmoudian, M. Ebadi, Solid-phase electrochemical reduction of graphene oxide films in alkaline solution, Nanoscale Research Letters, 8(2013) 1-9. [39] S. Sahoo, S. Dhibar, C.K. Das, Facile synthesis of polypyrrole nanofiber and its enhanced electrochemical performances in different electrolytes, Express Polym Lett, 6(2012) 965-74. [40] Z.H. Ibupoto, K. Khun, V. Beni, X. Liu, M. Willander, Synthesis of novel CuO nanosheets and their non-enzymatic glucose sensing applications, Sensors, 13(2013) 7926-38. [41] S. Cherevko, C.H. Chung, The porous CuO electrode fabricated by hydrogen bubble evolution and its application to highly sensitive non-enzymatic glucose detection, Talanta, 80(2010) 1371-7. [42] F. Cao, J. Gong, Nonenzymatic glucose sensor based on CuO microfibers composed of CuO nanoparticles, Anal Chim Acta, 723(2012) 39-44. [43] S. Stankovich, D.A. Dikin, G.H. Dommett, K.M. Kohlhaas, E.J. Zimney, E.A. Stach, et al., Graphene-based composite materials, Nature, 442(2006) 282-6. [44] B. Yuan, C. Xu, L. Liu, Q. Zhang, S. Ji, L. Pi, et al., Cu2O/NiOx/graphene oxide modified glassy carbon electrode for the enhanced electrochemical oxidation of reduced glutathione and nonenzyme glucose sensor, Electrochim Acta, 104(2013) 78-83. [45] H. Yu, X. Jian, J. Jin, X.-c. Zheng, R.-t. Liu, G.-c. Qi, Nonenzymatic sensing of glucose using a carbon ceramic electrode modified with a composite film made from copper oxide, overoxidized polypyrrole and multi-walled carbon nanotubes, Microchim Acta, (2014) 1-9. [46] S.K. Meher, G.R. Rao, Archetypal sandwich-structured CuO for high performance nonenzymatic sensing of glucose, Nanoscale, 5(2013) 2089-99. [47] X.J. Zhang, A.X. Gu, G.F. Wang, Y. Huang, H.Q. Ji, B. Fang, Porous Cu-NiO modified glass carbon electrode enhanced nonenzymatic glucose electrochemical sensors, Analyst, 136(2011) 5175-80. [48] Y. Zhang, Y. Wang, J. Jia, J. Wang, Nonenzymatic glucose sensor based on graphene oxide and electrospun NiO nanofibers, Sensors and Actuators B: Chemical, 171– 172(2012) 580-7. [49] J.Y. Huang, K. Wang, Z.X. Wei, Conducting polymer nanowire arrays with enhanced electrochemical performance, J Mater Chem, 20(2010) 1117-21.
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Table 1. A comparison of this work with the other works in the literature regarding the performance of the GLC measure
cr
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Table 2. Determination of GLC in real samples.
Modify Electrode
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Table 1 Performance
CuO/OPpy/MWCNTs/CCE
Liner range (mM)
an
LOD (µM) 0.05
Porous Cu–NiO NA/NiONF-rGO/GCE
[45]
Up to 3.2
[46]
Up to 8.0
[1]
0.5
0.5-5
[47]
0.77
0.002-0.6
[48]
0.4
[44]
te
d
6.2
Up to 2
M
Sandwich-structured CuO CuxO/Ppy/Au
References
0.87–2.95
Porous CuO
0.14
0.001-2.5
[41]
CuxO/Ppy/rGO
0.03
0.1-10
This work
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Cu2O/NiOx/GO/GC
Sample Number 1 2 3 4 5
Table 2.
Added (mM)
RSD%
0.1 0.5 1 5 50
0.872 1.239 0.995 0.968 1.036
Measured by biosensor (mM) 0.098 0.459 0.983 4.936 49.408
Recovery% 98.25 97.92 98.63 98.72 98.81
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References: [45] H. Yu, X. Jian, J. Jin, X.-c. Zheng, R.-t. Liu, G.-c. Qi, Nonenzymatic sensing of glucose using a carbon ceramic electrode modified with a composite film made from copper oxide, overoxidized polypyrrole and multi-walled carbon nanotubes, Microchim Acta, (2014) 1-9.
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[46] S.K. Meher, G.R. Rao, Archetypal sandwich-structured CuO for high performance non-enzymatic sensing of glucose, Nanoscale, 5(2013) 2089-99.
cr
[1] F.H. Meng, W. Shi, Y.N. Sun, X. Zhu, G.S. Wu, C.Q. Ruan, et al., Nonenzymatic biosensor based on CuxO nanoparticles deposited on polypyrrole nanowires for improving detection range, Biosensors & Bioelectronics, 42(2013) 141-7.
Ac ce p
te
d
M
an
us
[47] X.J. Zhang, A.X. Gu, G.F. Wang, Y. Huang, H.Q. Ji, B. Fang, Porous Cu-NiO modified glass carbon electrode enhanced nonenzymatic glucose electrochemical sensors, Analyst, 136(2011) 5175-80. [48] Y. Zhang, Y. Wang, J. Jia, J. Wang, Nonenzymatic glucose sensor based on graphene oxide and electrospun NiO nanofibers, Sensors and Actuators B: Chemical, 171–172(2012) 580-7. [44] B. Yuan, C. Xu, L. Liu, Q. Zhang, S. Ji, L. Pi, et al., Cu2O/NiOx/graphene oxide modified glassy carbon electrode for the enhanced electrochemical oxidation of reduced glutathione and nonenzyme glucose sensor, Electrochim Acta, 104(2013) 78-83. [41] S. Cherevko, C.H. Chung, The porous CuO electrode fabricated by hydrogen bubble evolution and its application to highly sensitive non-enzymatic glucose detection, Talanta, 80(2010) 1371-7.
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Authors Biography Pooria Mn is a Ph.D. candidate at the University of Malaya. His research interests
ip t
include the anti-corrosion coatings, automotive and industrial coatings, nanomaterials,
cr
composites, synthesis and electrochemistry of conducting polymers, sensors and actuators.
Pei Meng Woi is a senior lecturer in Department of Chemistry, Faculty of Science,
of
expertise
is
Bio-Inorganic
Chemistry
and
her
fields
of
interests
are
an
area
us
university of Malaya, Malaysia. She graduated her Ph.D. from University of Malaya (2011). Her
Electropolymerisation, Electrocatalysis. She is one of the members of the Royal Society
M
Chemistry, Member, 2012, (International).
d
Farnaz Lorestani is a Ph.D. candidate at the University of Malaya, after receiving her
te
MSc in Analytical Chemistry at 2011 and a BSc. degree in Applied Chemistry at 2007 from
Ac ce p
Ferdowsi University, Mashhad, Iran. Her research interests include nanomaterials, composites, chemical sensor and electrochemical sensors.
Page 21 of 30
Dr. M. R. Mahmoudian is a Lecturer with the Department of Chemistry, Shahid Sherafat, University of Farhangian, Tehran, Iran.
He obtained his Ph.D. degree from the
University of Malaya in 2011. His research interests include the synthesis and electrochemistry
ip t
of conducting polymers for anti-corrosion coatings, electrochemical devices, sensors and
cr
actuators.
Yatimah Alias is a Professor of Electrochemistry in Department of Chemistry, Faculty
us
of Science, University of Malaya, Malaysia. She graduated her Ph.D. from East Anglia
an
University, UK (1998). Her area of expertise is Electrochemistry and Coordination Chemistry and her fields of interests are Electrosynthesis, Polymer Electrolytes and Molecular Assemblies.
M
She is one of the members of the Malaysian Analytical Sciences Society (ANALISIS) and also
Ac ce p
te
d
the Electrochemical Society.
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Figure 1. Schematic diagram of modified electrode for glucose sensor Figure 2. (a) Electrodeposition of rGO on GCE in an aqueous solution of 7 mg L−1 GO and a 0.1 M phosphate buffer solution at the scan rate of 1 mV s-1. (b) FESEM of rGO/GCE (c) CVs of electropolymerization
on
the
surface
of
rGO/GCE
and
(d)
amperometry
ip t
Ppycv
electropolymerization of Ppy on the surface of rGO/GCE from an aqueous solution containing 0.1 M pyrrole, 0.1 M phosphate buffer solution and 0.1 M LiClO4 constant potential of 0.8 V for
cr
800 s .
us
Figure 3. FT-IR spectra for (a) GO, (b) rGO, (c) Ppyamp and (d) Ppyamp/rGO
Figure 4. (a) EDX spectra of Ppyamp/rGO and CuxO/Ppyamp/rGO. (b) XRD spectrum of
an
CuxO/Ppyamp/rGO.
Figure 5. (a) CVs of (1) the bare GCE (inset), (2) rGO/GCE (inset), (3) Ppycv/rGO/GCE, (4)
M
Ppyamp/rGO/GCE and (b) CVs of different concentrations of CuxO on the surface of Ppyamp/rGO/GCE in a 0.1 M phosphate buffer solution (pH = 7.2) and 1 mM glucose, scanned at
6.
FESEM
mM)/Ppyamp/rGO/GCE,
of
(a)
Ppycv/rGO/GCE,
te
Figure
d
applied potential ranged from -1 to 1 V at 50 mVs-1 scan rate.
(d)
CuxO
(30
(b)Ppyamp/rGO/GCE,
mM)/Ppyamp/rGO/GCE,
(c) (e)
CuxO CuxO
(10 (60
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mM)/Ppyamp/rGO/GCE and (f) CuxO (90 mM)/Ppyamp/rGO/GCE
Figure 7. (A) Nyquist plots of (a) bare electrode, (b) rGO/GCE, (c) Ppycv/rGO/GCE, (d)Ppyamp/rGO/GCE and (e) CuxO (10 mM)/Ppyamp/rGO/GCE (B) Bode plots of (a) bare electrode, (b) rGO/GCE, (c) Ppycv/rGO/GCE, (d)Ppyamp/rGO/GCE and (e) CuxO (10 mM)/Ppyamp/rGO/GCE.
Figure 8. (a) Current–time responses of CuxO/Ppyamp/rGO/GCE with successive increasing GLC concentration at +0.2V and the inset shows the dependence of the current response vs. GLC concentration and (b) Stability of the sensor stored at 4 ◦C over 2 weeks in PBS with addition of 1 mM GLC at +0.2 V vs SCE and the inset shows amperometric response of
Page 23 of 30
CuxO/Ppyamp/rGO/GCE upon the successive addition of 1 mM GLC, ascorbic acid, fructose, uric
Ac ce p
te
d
M
an
us
cr
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acid and lactose into 0.1 M PBS (pH 7.2) with an applied potential +0.2 V
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Figure 1.
Figure 2.
Page 25 of 30
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Figure 3.
Figure 4.
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Figure 5.
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Figure 6.
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Figure 8.
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S0925-4005(14)01452-X http://dx.doi.org/doi:10.1016/j.snb.2014.11.072 SNB 17713
To appear in:
Sensors and Actuators B
Received date: Revised date: Accepted date:
22-9-2014 3-11-2014 12-11-2014
Please cite this article as: P. Mn, W.P. Meng, F. Lorestani, M.R. Mahmoudian, Y. Alias, Electrodeposition of copper oxide/polypyrrole/reduced graphene oxide as a nonenzymatic glucose biosensor, Sensors and Actuators B: Chemical (2014), http://dx.doi.org/10.1016/j.snb.2014.11.072 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Electrodeposition of copper oxide/polypyrrole/reduced graphene oxide as a
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nonenzymatic glucose biosensor
Pooria Mna,*, Woi Pei Menga, Farnaz Lorestania, MR Mahmoudianb, Y. Aliasa,*
Department of Chemistry, Shahid Sherafat, University of Farhangian, 15916 Tehran, Iran
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b
Department of Chemistry, University of Malaya, Kuala Lumpur 50603, Malaysia
cr
a
Email: [email protected]; [email protected]; [email protected];
an
[email protected]; [email protected]
M
*Authors to whom correspondence should be addressed; Email: [email protected];
Abstract report
the
synthesis
Ac ce p
We
te
d
[email protected]; Tel: +603-79676774; Fax: +603-79674188
and
application
of
copper
oxide/polypyrrole
nanofiber/reduced graphene oxide nanocomposite (CuxO/Ppy/rGO/GCE) for the detection of glucose (GLC). CuxO, Ppy and rGO were synthesized via electrodeposition process. The formation of the rGO and Ppy were approved by Fourier Transform Infrared Spectroscopy (FT-IR). Energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) confirmed the formation of copper oxide. The field emission scanning electron microscopy (FESEM) images depicted the existence of wrinkle rGO, Ppy nanofibers with diameter around 100 nm and the uniformity of the CuxO particles deposited on the Ppy nanofibers. Electrochemical impedance spectroscopy (EIS) data also indicated the charge transfer of each layer decreased compared to the underneath layer. By using cyclic voltammetry (CV) and
Page 1 of 30
chronoamperometry under pH 7.2, the electrocatalytic activity of CuxO/Ppy/rGO/GCE towards GLC was explored. The sensor presented a linear range of 0.1 to 100 mM (R2=0.991) of GLC, that is higher than most of the present nonenzymatic glucose biosensors based on
ip t
CuxO, Ppy and rGO. The limit of detection (LOD) reaches 0.03 µM (at S/N=3). Additionally, the sensor exhibited remarkable reproducibility, stability and selectivity properties which
us
cr
make CuxO/Ppy/rGO/GCE a good nonenzymatic GLC sensor.
Keywords: Copper oxide; Polypyrrole; Reduced Graphene Oxide; Glucose; Nonenzymatic
M
an
biosensor
1. Introduction
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More than 220 million of people around the world are suffering from diabetes which
te
is a highly extensive disease bringing about metabolic disorders. Testing the blood glucose
Ac ce p
(GLC) is very crucial for diabetic patients and helps to evade the clustering of blood GLC (in the range of 4.4–6.6mM). Therefore it is of high significance to establish straightforward system with high sensitivity, selectivity and stability in order to distinguish GLC levels.[1-3] Graphite oxide was primarily recorded 150 years ago and reappeared tremendously in the studies due to the low cost and volume production of graphene-based materials. The layered structure of graphite oxide is similar to graphite’s structure but in graphite oxide, the sheet of carbon atoms is densely decorated by groups which contain oxygen, which besides increasing the interlayer distance, it makes the atomic-thick layers hydrophilic. Therefore, this is resulted to the exfoliation of oxidized layers in water under moderate ultra-sonication [4-9]. It also should be mentioned that the most interesting feature of GO is being partly reduced to
Page 2 of 30
graphene-like sheets through the removal of the groups which contain oxygen with the recovery of a conjugated structure [7, 8, 10-12]. In 1977 H.Shirakawa et al [13] reported electrical conductivity in a conjugated
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polymer and since then conducting polymers have been largely explored due to their unique electrical characteristics. Polypyrrole, among the conducting polymers is specifically
cr
advantageous for its different financial applications like chemical sensors [14, 15],
us
supercapacitors [15-17], biosensors [2, 6, 7, 18, 19], gas sensors [20] and corrosion protection [21-23] because of being environmentally stable, electrically conductive and flexible.
an
Recently a huge attempt has been made to expand polypyrrole nanostructures which exhibit unique physical and chemical characteristics preferable to their bulky counterpart and that is
technology [24-27].
M
due to an expanding need for conducting polymers in the field of nano-science and Electrochemical polymerization provides a one-step procedure and
d
offers precise control of the thickness and the structure of the resulting film [28].
te
Transition metal oxides, like Cu2O are drawing a huge attention as sensors for
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detection of glucose because of their good characteristics such as low cost, ease of synthesis and post synthesis handling, stability, remarkable redox process at different potential ranges under several reaction conditions. Electrodes based on CuO or Cu2O (CuxO) showed a high electrocatalytic oxidation ability for GLC [29]. In the present paper, two different types of Ppy nanofibers, modified by CuxO (CuO
and Cu2O composite) nanoparticles were well prepared on reduced graphene oxide. Stability, sensitivity, reproducibility and high range of detection are the properties of the prepared biosensors which integrated the properties of rGO, Ppy and transition metal oxide.
2.
Experimental details
Page 3 of 30
2.1.
Materials All of the materials including D-(+)-glucose, potassium hydrogen phosphate (99%),
lithium perchlorate (99%), pyrrole (99.5%), potassium dihydrogen phosphate (99%) and
ip t
copper(II) chloride dehydrate (99%) were purchased from Sigma–Aldrich and were used in
2.2.
cr
the form which they were received.
Instruments
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All the electrochemical measurement including electrochemical impedance
an
spectroscopy (EIS), chronoamperometry and cyclic voltammetry (CV) were performed using a potentiostat/ galvanostat model PGSTAT-302N from the Autolab controlled by a USB
M
IF030 (Metrohm Autolab) interface. A counter electrode, reference electrode and a working electrode formed a three-electrode compartment cell. SCE saturated KCl was the reference
d
electrode for all the potentials. X-ray powder diffraction (XRD; Philips X’pert system using
te
Cu Ka radiation), was used for characterizing the crystal phase. For morphologies comparison, the field emission scanning electron microscopy (FESEM) images were taken by
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exploiting FESEM, Quanta 200F. To perform Fourier Transform Infrared spectroscopy (FTIR) a spectrum 400 FT-IR/FT-FIR spectrometer was used.
2.3.
Preparation of the nonenzymatic GLC sensor
In order to fabricate the nonenzymatic biosensor, glassy carbon electrode was chosen
to act as the base electrode. By using alumina (under 1, 0.1 and 0.05 mm diameter) slurries in the pre-experiment preparations, the clean GCE was polished to a mirror and subsequently washed by water which was previously distilled twice and ultrasonicated in ethanol and distilled water for ten minutes respectively. To be ready for use, it was dried under high purity N2 gas flow.
Page 4 of 30
By exploiting a modified Hummers’ method, GO was synthesized [30]. The graphene oxide (GO) was deposited and reduced simultaneously on the glassy carbon surface via CV by scanning repetitively from 0 to -1.5 V vs SCE at scan rate of 1 mVs-1 in a solution
ip t
composed of 7 mg L-1 graphene oxide and 0.1 M phosphate buffer (PBS) at pH 7.2. The electropolymerization of Ppy nanofibers on the surface of coated GCE with rGO
cr
was performed in two different methods:
First, by cyclic voltammetry in a single compartment cell, with the applied potential
us
ranging from 0.0 to 0.8 V at a scan rate of 1 mV s−1, the electropolymerization was performed
an
in 4 voltammetric cycles on the surface of rGO.
Second, amperometry was the method used for the electrodeposition of polypyrrole
M
on the surface of rGO at the constant potential of 0.8 V for 800 s. The monomer solution for both methods contains mixed electrolytes in a 0.1 M phosphate
d
buffer solution (pH 7.2), 0.1 M pyrrole monomer and 0.1 M LiClO4.
te
Before oxidization by CV scan, in a solution containing 0.1 M KCl and four different concentrations of CuCl2 (10, 30, 60, 90 mM), the Cu nanoparticles were electrodeposited on
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the surface of modified electrode at the constant potential of -0.6 V. Right after this stage, in order to permit the Cu nanoparticles to enter the oxidation form (CuxO), CV was performed in 0.1 M NaOH solution at the applied range of -0.5 to 0.3 V at a scan rate of 50 mVs-1 for 40 cycles [1, 31].
To eliminate the O2, the electrolyte was purged before conducting the experiments for
10 min with highly purified N2 and after the experiments, the modified electrodes were washed for several times and dried with a flow of N2. Fig. 1 shows the process of the study schematically.
Fig. 1
Page 5 of 30
3.
Results and discussion
3.1.
Electrodeposition of rGO, Ppy and CuxO
ip t
Fig. 2(a) shows the first cycle among the four cycles of the electrochemical deposition of rGO layer. As can be seen and also mentioned in the previous studies [32-34], one anodic
cr
and two cathodic peaks can be recognized. The electrochemical reduction of GO which is reversible is responsible for the cathodic current peak III. In contrast, the oxidation reduction
us
pair of some electrochemically active oxygen-containing groups on graphene planes is
an
responsible for anodic peak I and cathodic peak II. These active oxygen-containing groups cannot be eliminated by cyclic voltammetry method from the graphene sheets [35, 36]. The
M
SEM image (Fig. 2(b)) confirms the formation of rGO film on GCE. The image of FESEM displays that the surface of GCE electrode with modified rGO is wrinkled and rough due to
d
the formation of rGO. This can be justified as in the course of electrodeposition, when the
te
electrode potential decreased to negative, GO was electrochemically reduced to form rGO which is extremely hydrophobic [37].
Ac ce p
The electropolymerization of Ppy nanofibers has been performed with two methods
with the same materials. Fig. 2(c) shows the first four successive cyclic voltammograms of the rGO/GCE. The process of monomer oxidation starts as the potential increases to 0.65 V vs. SCE, in the anodic scan of the first cycle on the surface of rGO/GCE with mixed electrolyte is composed of 0.1 M phosphate buffer solution, 0.1 M pyrrole monomers and 0.1 M LiClO4 at the scan rate of 1 mVs-1. The faster scan rate will lead to a shorter reaction time for each scan cycle and thus the increment of the film’s radius in a faster scan cycle is less than that of a slower scan cycle [26]. Fig. 2(d) shows the electropolymerization process with amperometry method. As can be seen, as electropolymerization process starts, a noticeable increase in the current is observed
Page 6 of 30
suggesting that a conductive polypyrrole has been formed and after around 50 s, the current reaches the steady state condition.
ip t
Fig. 2
The FT-IR spectrum of the GO, rGO, Ppyamp and Ppyamp/rGO are shown in Fig. 3 (a,
cr
b, c, d), respectively. For GO, the broad peak centered at 3363 cm-1 is assigned to the O-H
us
stretching vibrations while the peaks at 1740, 1630 and 1431 are attributed to C=O stretching, sp2-hybridized C=C group and O-H bending, C-OH stretching [38]. In addition, the peak at
an
1050 cm-1 can be attributed to C-O vibration of epoxy or alkoxy groups. The peaks at 3299 and 3295 cm−1 in the Ppyamp and Ppyamp/rGO spectra (Fig. 3(c) and (d)) are attributed to N–H
M
stretching vibrations of the pyrrole ring. The peak at 3361 cm−1 in the rGO spectra is related to O–H groups and the bands at 1753 and 1477 cm−1 are related to C-O and C-OH,
d
respectively (Fig. 3(b)). The peaks at 1260 and 1067 cm−1 in the rGO spectrum are
te
recognized as the C-O stretching vibration of the epoxy and alkoxy groups, respectively [27].
Ac ce p
The peaks at 2938 and 2860 cm−1 in the rGO spectrum are related to the CH2 asymmetric and symmetric stretching vibrations, respectively. The peaks at 1703 and 1653 cm−1 are related to C-N-C bond in the Ppyamp and Ppyamp/rGO spectra in Fig. 3(c) and (d), respectively. The bands at 1570 and 1510 cm−1 are related to the C–C and C–N in the Ppyamp and Ppyamp/rGO spectra, respectively [39]. The peaks at 1471 and 1421 cm−1 are recognized as typical Ppy ring vibrations (Fig. 3(c) and (d)), respectively. The aliphatic C-H peaks (at 2866 and 2930 cm−1 in the Ppyamp/rGO spectrum) and the peaks representing the C-O stretching vibration of the epoxy (at 1270 and 1052 cm−1) and alkoxy groups (at 1268 and 1063 cm−1) in Ppyamp/rGO spectra, respectively, confirm the existence of rGO.
Fig. 3
Page 7 of 30
EDX analysis was employed to prove the elemental composition at various stages. Fig. 4(a) displays the EDX spectra of Ppyamp/rGO/GCE and CuxO/ Ppyamp/rGO/GCE.
ip t
Elemental Cu is detected in CuxO/ Ppyamp/rGO/GCE, although it is not present in the unmodified Ppyamp/rGO/GCE. This supports the point that Cu was able to be successfully
cr
deposited onto Ppy nanofibers.
XRD analysis was employed to affirm the composition of CuxO electrodeposited on
us
the surface of Ppy nanofibers. Fig. 4(b) presents the XRD patterns of the CuxO/Ppyamp/rGO.
an
The diffraction peaks which have been obtained for CuxO/Ppyamp/rGO are in the same manner with the preceding recorded standards [40, 41]. No peak has been observed for Cu
M
which shows that the Cu deposited on Ppy was fully changed into CuO and Cu2O composite
d
[42].
te
Fig. 4
Ac ce p
Fig. 5 displays the cyclic voltammetry of the bare GCE (inset), rGO/GCE (inset),
Ppyamp/rGO/GCE, Ppycv/rGO/GCE, in a 0.1 M phosphate buffer solution (pH = 7.2) and 1 mM concentration. Compared to the bare GCE, the rGO/GCE indicates a rise in the anodic and cathodic current. Mahmoudian [27] presented that the presence of rGO increases the conductivity of the system. The CVs of Ppycv/rGO/GCE and Ppyamp/GCE reveal a redox couple in the anodic and also cathodic scans. The doping/dedoping process of Ppy nanofibers is responsible for the peaks. When a positive potential is employed, the counter ions are occupied (doping) and later the anions make the positive charges of Ppy nanofibers balanced. In contrary, when a sufficient negative potential is used for the polymer, the counter ions are freed (de-doping). Fig. 5 (a (3, 4)) indicates the influence of the electropolymerization
Page 8 of 30
method on the electrocatalytic activity of the Ppy towards GLC oxidation. By comparing the CVs of Ppycv/rGO/GCE with Ppyamp/rGO/GCE, it will be approved that compared with CV method, synthesizing Ppy with amperometry shows much more sensitivity toward GLC.
ip t
Fig. 5(b) displays the CVs of different concentrations of CuxO on the surface of Ppyamp/rGO/GCE in a 0.1 M phosphate buffer solution (pH = 7.2) and 1 mM glucose,
cr
scanned at applied potential ranged from -1 to 1 V at scan rate of 50 mVs-1. As can be seen,
us
10 mM concentration of Cu is the best compared with the others. FESEM images (Fig. 6) also confirm the result.
an
It is notable that during the electropolymerization, the overoxidation of Ppy may occur. Therefore the overoxidized Ppy can be reduced by the oxidation of GLC during their
M
interaction.
d
(1)
Ac ce p
te
Fig. 5
As can be seen in FESEM Fig. 6 (a, b), the surface morphologies of the amperometry
Ppy nanofibers matrix and cyclic voltammetry Ppy were characterized. Fig. 6(b) presents clear and comparatively smooth amperometry Ppy nanofibers in diameter of ~100 nm, more stretched than cyclic voltammetry Ppy. Fig. 6(a) shows that a larger surface area can be detected in amperometry method. The amperometry Ppy nanofibers have a well-arranged polymer chain structure with greatly high ratio of surface-to-volume that is useful for the decorating by CuxO particles. The FESEM of Ppycv (Fig. 6(a)) indicates that as a result of the variation of applied potential, the film formation is not homogenous. Besides, the existence of non-homogeneous polypyrrole confirms that the conditions of polymerization highly influence the morphology of the film [26]. The reason for homogeneity of Ppyamp is not
Page 9 of 30
similar to CV method. In CV method monomers meet a wider potential ranges which are not necessarily monomer oxidation, then polymers with various lengths are made and apparently they are not uniformed. While in amperometry method, monomers are exposed to oxidation
ip t
potential very fast. The morphologies of the CuxO/Ppyamp/rGO/GCE composites with various
cr
concentrations of Cu nanoparticles are displayed in Fig. 6 (c, d, e, and f). It can be seen that 10 mM concentration of Cu is the best compared with the others in which CuxO particles are
us
uniformly attached on the surface of Ppyamp nanofibers. These morphological features
an
provide several beneficial properties, such as, more available active sites, high catalysis properties and large surface area of CuxO/Ppyamp/rGO/GCE for GLC oxidation. The FESEM
M
also confirms that the agglomeration of CuxO took place with increasing the concentration of Cu nanoparticle.
d
It should be mentioned that different scales were used to show how much
te
agglomeration occurred in each concentration. As can be seen in Fig. 6 (b), the diameter of each fiber is almost 100 nm. Fig. 6(c) is also in the same scale and shows that the copper
Ac ce p
oxide particles uniformly covered each Ppy nanofiber. With increasing concentration (Fig. 6(d and e)), wider scales were chosen in order to show that the agglomerated particles were becoming bigger compared with Ppy nanofibers. In Fig. 6(f), all the copper oxide particles completely covered the surface so that there is no Ppy nanofiber to be distinguished.
Fig. 6
In order to analyze the impedance changes of the modified electrode, electrochemical impedance spectroscopy was employed. Fig. 7(A) depicts the Nyquist plots in 0.1 M KCl solution containing 1 mM Fe[(CN)6]3−/4− (1:1). The Nyquist plot of impedance spectra
Page 10 of 30
consists of semicircle portion which at higher frequencies correlates to the electron transfer limited process while on the other hands, a linear portion at lower frequencies correlates to the diffusion process. The electron transfer resistance (Rct), by using the diameter of the
ip t
semicircle diameter can be evaluated. The results confirmed that the alteration of GCE by reduced graphene oxide makes
cr
the resistance of charge transfer extremely reduced which can be interpreted due to the fact that the rGO layer protects various small band gaps which are agreeable for the electron
us
conduction [43]. Moreover, the comparison between the semicircle diameters from the
an
Nyquist diagrams of CuxO/Ppyamp/rGO/GCE (1529 Ω), Ppyamp/rGO/GCE (429 Ω), Ppycv/rGO/GCE (2341 Ω) and rGO/GCE (19781 Ω) shows the direction of Rct:
M
(Rct): GCE> rGO/GCE> Ppycv/rGO/GCE> CuxO/Ppyamp/rGO/GCE > Ppyamp/RGO/GCE The main reason for increasing the charge transfer in CuxO/Ppyamp/rGO/GCE
te
conductivity [1, 44].
d
compared with Ppyamp/RGO/GCE is that CuxO is a p-type semiconductor which has poor
In order to figure out the impedance parameters, the ZSimp Win software is
Ac ce p
employed in the simulations. The Rs(CPE[RctW)]) equivalent circuit model was employed in the simulation of the impedance behavior of all the modified electrodes, from the experimentally gained impedance data. By exploiting the series components, the model was developed. The first component is ohmic resistance of the solutions of the electrolyte Rs and the second one is a set of constant phase elements (CPE) and the resistance of layer which indicates the conductivity of the sample (Rct) that are in the parallel position. And additionally from the diffusion impedance, W for the Warburg element is a series connection to Rct.
Fig. 7
Page 11 of 30
Fig. 7(B) shows the Bode plot that is in agreement with results obtained from Nyquist
3.2.
ip t
plot.
Optimization of the sensor
cr
In order to find the best potential, the relationship between the oxidation current of GLC and the applied potential was measured. To find proper potential for amperometric
us
response, the applied potential of the CuxO/Ppyamp/rGO/GCE was evaluated over the range of -0.2 to 0.4 V. Finally +0.2 V was selected as the optimized potential. Fig. 8a indicates the
an
amperometric responses at +0.2 V of CuxO/Ppyamp/rGO/GCE electrode with subsequently adding in GLC concentration from 0.1 to 100 mM. The comparable calibration curve is
M
shown in Fig 8a (inset). The relationship between the current and the concentration which is linear, is settled in the concentration range from 0.1 to 100 mM (R2=0.996).
d
The linear part increases from 0.1 mM to 100 mM (Fig 8a) with a linear regression
te
equation of I = 141.21 (µA.mM−1) + 114.32 (R2= 0.9991). The following equations were used
Ac ce p
for calculating the limit of detection (LOD) and the limit of quantification (LOQ) of CuxO/Ppyamp/rGO/GCE:
(2) (3)
Where SB is the standard deviation of the blank solution and b is the slope of the calibration curve. The LOD and LOQ (S/N of 3) are estimated to be 0.03 µM and 0.11 µM for the linear part, respectively.
3.3.
Stability and reproducibility of CuxO/Ppyamp/rGO/GCE
Page 12 of 30
The studied sensor shows a good stability, with a loss of only 10.4% in current response after 2 weeks at 4 ◦C (Fig 8b). By measuring the response to 1 mM glucose over 1 month, the long term stability of sensor was studied. The sensor was kept in the atmosphere
ip t
and for 10 first days, it was tested every day and the next 20 days, every 5 days. The results indicate that the response was relatively the same over the entire examination days,
cr
suggesting that the sensor can be used in long term applications.
It should be added that for five electrodes which have been made identically with a relative
us
standard deviation (RSD) of 4.3% the reproducibility was explored, while 10 measurements
an
for the same electrode were carried out by adding 1 mM GLC with RSD of 6.4%, showing
3.4.
M
high repeatability.
Interference study
d
Successive addition of 1 mM GLC, fructose, ascorbic acid, uric acid and lactose into
te
0.1 M phosphate buffer solution (pH 7.2) was used for CuxO/Ppyamp/rGO/GCE in order to study the effect of common interfering species (Fig. 8b (inset)). As can be seen, the current of
Ac ce p
these interfering species does not reveal an obvious additional signal which indicates that this modified electrode has a good selectivity towards GLC. There is a comparison between the performance of the CuxO/Ppyamp/rGO/GCE and
those of previously reported nonenzymatic GLC sensors based on CuxO, Ppy and rGO in Table 1. The linear range of prepared sensor (0.1 –100 mM) is considerably greater than that of other CuxO, Ppy and rGO [1, 41, 44-48], making CuxO/Ppyamp/rGO/GCE high potential for industrialization. The high sensitive catalytic performance, the wide linear range and low detection limit can be attributed to the nature of CuxO based on Ppy nanofibers and moreover the existing rGO as a substrate for upper layer which increase the conductivity of the system. Comparing the CuxO modified electrode and CuO/Cu2O-modified electrode, it was found that
Page 13 of 30
due to the synergic effect of CuO and Cu2O (CuxO), the latter has a wider linear detection range towards electrocatalytic oxidation of GLC [49]. Furthermore, CuxO particles can finely cover the Ppy nanofibers and the CuxO can highly raise the electrocatalytic active areas and
GLC molecules to be detected, adequately enhanced electrons.
cr
Fig. 8
ip t
enhance electron transfer. Additionally, the Ppy nanofibers can provide larger surface area for
us
Table 1
an
In order to find out the accuracy of the sensor, the sensor was applied to real blood serum samples for determination of GLC. By employing standard addition method, GLC in human
M
blood was determined on the modified sensor. Before measuring the current response, 0.04 mL of the samples (contains 4.4-6.4 mM GLC) were diluted by 10 mL phosphate buffer solution
d
(pH 7.2) and then GLC solutions were added one after another to the system. All the
te
measurements were carried out five times and the results are listed in Table 2. The calculated
Ac ce p
recovery and relative standard deviation (RSD) values from Table 2 show that the prepared sensor possesses potential applications in determining certain concentration range of GLC.
4.
Table 2
Conclusion
CuxO/Ppy/rGO/GCE have been successfully prepared via an in-situ electrochemical
deposition process. XRD, FT-IR and EDX results confirmed the presence of CuxO, Ppy nanofibers and rGO. The FESEM images of the modified electrode revealed the existence of rGO, Ppy nanofibers and finally CuxO was formed uniformly and fully covered the nanofibers. The electrochemical behavior of GCE coated with the CuxO/Ppy/rGO/GCE film
Page 14 of 30
showed the highest electrocatalytic activity compared with other modified GCE. The impedance data confirmed that the charge transfer resistance (Rct) of the modified electrode was significant. CuxO/Ppy/rGO/GCE electrochemical sensor had a wide linear range up to
ip t
100 mM GLC concentration, a high sensitivity and a low detection limit of 0.03 µM. These great performances including high selectivity and sensitivity, easy fabrication and especially
cr
wide linear range, make CuxO/Ppy/rGO/GCE an excellent amperometric sensor for
us
determining glucose concentration.
an
Acknowledgments
The researcher named Pooria Mn wishes to thank Mahtab Mahdavifar for precious This
research
is
supported
by
High
Impact
Research
MoE
Grant
M
reviews.
UM.C/625/1/HIR/MoE/SC/04 from the Ministry of Education Malaysia, UMRG Program
Ac ce p
te
d
RP012A-13SUS and University Malaya Centre for Ionic Liquids (UMCiL).
Page 15 of 30
References:
Ac ce p
te
d
M
an
us
cr
ip t
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Page 18 of 30
Table 1. A comparison of this work with the other works in the literature regarding the performance of the GLC measure
cr
ip t
Table 2. Determination of GLC in real samples.
Modify Electrode
us
Table 1 Performance
CuO/OPpy/MWCNTs/CCE
Liner range (mM)
an
LOD (µM) 0.05
Porous Cu–NiO NA/NiONF-rGO/GCE
[45]
Up to 3.2
[46]
Up to 8.0
[1]
0.5
0.5-5
[47]
0.77
0.002-0.6
[48]
0.4
[44]
te
d
6.2
Up to 2
M
Sandwich-structured CuO CuxO/Ppy/Au
References
0.87–2.95
Porous CuO
0.14
0.001-2.5
[41]
CuxO/Ppy/rGO
0.03
0.1-10
This work
Ac ce p
Cu2O/NiOx/GO/GC
Sample Number 1 2 3 4 5
Table 2.
Added (mM)
RSD%
0.1 0.5 1 5 50
0.872 1.239 0.995 0.968 1.036
Measured by biosensor (mM) 0.098 0.459 0.983 4.936 49.408
Recovery% 98.25 97.92 98.63 98.72 98.81
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References: [45] H. Yu, X. Jian, J. Jin, X.-c. Zheng, R.-t. Liu, G.-c. Qi, Nonenzymatic sensing of glucose using a carbon ceramic electrode modified with a composite film made from copper oxide, overoxidized polypyrrole and multi-walled carbon nanotubes, Microchim Acta, (2014) 1-9.
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[46] S.K. Meher, G.R. Rao, Archetypal sandwich-structured CuO for high performance non-enzymatic sensing of glucose, Nanoscale, 5(2013) 2089-99.
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[1] F.H. Meng, W. Shi, Y.N. Sun, X. Zhu, G.S. Wu, C.Q. Ruan, et al., Nonenzymatic biosensor based on CuxO nanoparticles deposited on polypyrrole nanowires for improving detection range, Biosensors & Bioelectronics, 42(2013) 141-7.
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an
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[47] X.J. Zhang, A.X. Gu, G.F. Wang, Y. Huang, H.Q. Ji, B. Fang, Porous Cu-NiO modified glass carbon electrode enhanced nonenzymatic glucose electrochemical sensors, Analyst, 136(2011) 5175-80. [48] Y. Zhang, Y. Wang, J. Jia, J. Wang, Nonenzymatic glucose sensor based on graphene oxide and electrospun NiO nanofibers, Sensors and Actuators B: Chemical, 171–172(2012) 580-7. [44] B. Yuan, C. Xu, L. Liu, Q. Zhang, S. Ji, L. Pi, et al., Cu2O/NiOx/graphene oxide modified glassy carbon electrode for the enhanced electrochemical oxidation of reduced glutathione and nonenzyme glucose sensor, Electrochim Acta, 104(2013) 78-83. [41] S. Cherevko, C.H. Chung, The porous CuO electrode fabricated by hydrogen bubble evolution and its application to highly sensitive non-enzymatic glucose detection, Talanta, 80(2010) 1371-7.
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Authors Biography Pooria Mn is a Ph.D. candidate at the University of Malaya. His research interests
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include the anti-corrosion coatings, automotive and industrial coatings, nanomaterials,
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composites, synthesis and electrochemistry of conducting polymers, sensors and actuators.
Pei Meng Woi is a senior lecturer in Department of Chemistry, Faculty of Science,
of
expertise
is
Bio-Inorganic
Chemistry
and
her
fields
of
interests
are
an
area
us
university of Malaya, Malaysia. She graduated her Ph.D. from University of Malaya (2011). Her
Electropolymerisation, Electrocatalysis. She is one of the members of the Royal Society
M
Chemistry, Member, 2012, (International).
d
Farnaz Lorestani is a Ph.D. candidate at the University of Malaya, after receiving her
te
MSc in Analytical Chemistry at 2011 and a BSc. degree in Applied Chemistry at 2007 from
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Ferdowsi University, Mashhad, Iran. Her research interests include nanomaterials, composites, chemical sensor and electrochemical sensors.
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Dr. M. R. Mahmoudian is a Lecturer with the Department of Chemistry, Shahid Sherafat, University of Farhangian, Tehran, Iran.
He obtained his Ph.D. degree from the
University of Malaya in 2011. His research interests include the synthesis and electrochemistry
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of conducting polymers for anti-corrosion coatings, electrochemical devices, sensors and
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actuators.
Yatimah Alias is a Professor of Electrochemistry in Department of Chemistry, Faculty
us
of Science, University of Malaya, Malaysia. She graduated her Ph.D. from East Anglia
an
University, UK (1998). Her area of expertise is Electrochemistry and Coordination Chemistry and her fields of interests are Electrosynthesis, Polymer Electrolytes and Molecular Assemblies.
M
She is one of the members of the Malaysian Analytical Sciences Society (ANALISIS) and also
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the Electrochemical Society.
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Figure 1. Schematic diagram of modified electrode for glucose sensor Figure 2. (a) Electrodeposition of rGO on GCE in an aqueous solution of 7 mg L−1 GO and a 0.1 M phosphate buffer solution at the scan rate of 1 mV s-1. (b) FESEM of rGO/GCE (c) CVs of electropolymerization
on
the
surface
of
rGO/GCE
and
(d)
amperometry
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Ppycv
electropolymerization of Ppy on the surface of rGO/GCE from an aqueous solution containing 0.1 M pyrrole, 0.1 M phosphate buffer solution and 0.1 M LiClO4 constant potential of 0.8 V for
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800 s .
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Figure 3. FT-IR spectra for (a) GO, (b) rGO, (c) Ppyamp and (d) Ppyamp/rGO
Figure 4. (a) EDX spectra of Ppyamp/rGO and CuxO/Ppyamp/rGO. (b) XRD spectrum of
an
CuxO/Ppyamp/rGO.
Figure 5. (a) CVs of (1) the bare GCE (inset), (2) rGO/GCE (inset), (3) Ppycv/rGO/GCE, (4)
M
Ppyamp/rGO/GCE and (b) CVs of different concentrations of CuxO on the surface of Ppyamp/rGO/GCE in a 0.1 M phosphate buffer solution (pH = 7.2) and 1 mM glucose, scanned at
6.
FESEM
mM)/Ppyamp/rGO/GCE,
of
(a)
Ppycv/rGO/GCE,
te
Figure
d
applied potential ranged from -1 to 1 V at 50 mVs-1 scan rate.
(d)
CuxO
(30
(b)Ppyamp/rGO/GCE,
mM)/Ppyamp/rGO/GCE,
(c) (e)
CuxO CuxO
(10 (60
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mM)/Ppyamp/rGO/GCE and (f) CuxO (90 mM)/Ppyamp/rGO/GCE
Figure 7. (A) Nyquist plots of (a) bare electrode, (b) rGO/GCE, (c) Ppycv/rGO/GCE, (d)Ppyamp/rGO/GCE and (e) CuxO (10 mM)/Ppyamp/rGO/GCE (B) Bode plots of (a) bare electrode, (b) rGO/GCE, (c) Ppycv/rGO/GCE, (d)Ppyamp/rGO/GCE and (e) CuxO (10 mM)/Ppyamp/rGO/GCE.
Figure 8. (a) Current–time responses of CuxO/Ppyamp/rGO/GCE with successive increasing GLC concentration at +0.2V and the inset shows the dependence of the current response vs. GLC concentration and (b) Stability of the sensor stored at 4 ◦C over 2 weeks in PBS with addition of 1 mM GLC at +0.2 V vs SCE and the inset shows amperometric response of
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CuxO/Ppyamp/rGO/GCE upon the successive addition of 1 mM GLC, ascorbic acid, fructose, uric
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M
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acid and lactose into 0.1 M PBS (pH 7.2) with an applied potential +0.2 V
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Figure 1.
Figure 2.
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Figure 3.
Figure 4.
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Figure 5.
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Figure 6.
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Figure 8.
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