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New electrochemical sensor based on Ni-doped V2O5 nanoplates modified glassy carbon electrode for selective determination of dopamine at nanomolar level
Accepted Manuscript Title: New electrochemical sensor based on Ni-doped V2 O5 nanoplates modified glassy carbon electrode for selective determination of dopamine at nanomolar level Author: R. Suresh K. Giribabu R. Manigandan S. Praveen Kumar S. Munusamy S. Muthamizh A. Stephen V. Narayanan PII: DOI: Reference:
S0925-4005(14)00634-0 http://dx.doi.org/doi:10.1016/j.snb.2014.05.095 SNB 16969
To appear in:
Sensors and Actuators B
Received date: Revised date: Accepted date:
28-2-2014 13-5-2014 22-5-2014
Please cite this article as: R. Suresh, K. Giribabu, R. Manigandan, S.P. Kumar, S. Munusamy, S. Muthamizh, A. Stephen, V. Narayanan, New electrochemical sensor based on Ni-doped V2 O5 nanoplates modified glassy carbon electrode for selective determination of dopamine at nanomolar level, Sensors and Actuators B: Chemical (2014), http://dx.doi.org/10.1016/j.snb.2014.05.095 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.
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New electrochemical sensor based on Ni-doped V2O5 nanoplates modified glassy carbon electrode for selective determination of dopamine at
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nanomolar level R. Suresh1, K. Giribabu1, R. Manigandan1, S. Praveen Kumar1, S. Munusamy1, S. Muthamizh1, A. Stephen2, and V. Narayanan1*
Department of Inorganic Chemistry, University of Madras, Guindy Maraimalai Campus,
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Chennai 600 025, India.
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Department of Nuclear Physics, University of Madras, Guindy Maraimalai Campus, Chennai
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600 025, India
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Address for Correspondence*
Assistant Professor, School of Chemical Sciences,
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Department of Inorganic Chemistry,
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Dr. V. Narayanan,
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University of Madras, Guindy Maraimalai Campus, Chennai 600 025, Tamil Nadu, India. Phone: 91 44 22202793; Fax: 91 44 22300488. Email: [email protected] (V. Narayanan).
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Abstract Ni-doped(0, 2, 5 and 7 wt%)V2O5 nanoparticles were prepared by thermal decomposition method. The as-prepared nanoparticles are characterized by X-ray diffraction (XRD), Fourier infrared
spectroscopy
(FTIR), Raman spectroscopy, UV-Vis absorption
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transformed
spectroscopy, scanning electron microscopy (SEM) and high resolution-transmission electron
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microscopy (HR-TEM). The results indicated that the Ni2+ ions are well doped within V2O5
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lattices. Compared with pure V2O5, Ni-doped V2O5 (Ni-V2O5) nanoparticles exhibit enhanced dopamine (DA) sensing property. Particularly, 7%Ni-V2O5 nanoplates modified glassy carbon
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electrode (7%Ni-V2O5/GCE) showed a good response to the DA concentration in the range of 6.6 to 96.4 µM with sensitivity of 132 nAµM-1. The obtained limit of detection (LOD) is 28 nM
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(S/N = 3). A possible mechanism related to the electrochemical oxidation of DA was proposed.
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Further, the proposed method was successfully utilized to determine DA in dopamine
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hydrochloride solution (11 to 13 µM) and reasonable results were obtained. The results showed that the exhibits an excellent electrocatalytic activity, good sensitivity, reproducibility,
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repeatability and long-term stability.
Keywords: Ni-doped V2O5, thermal decomposition, nanoplates, dopamine, modified electrode
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1 Introduction Dopamine (DA) is an electroactive neurotransmitter and plays a vital role in the function of the central nervous system in mammalian [1]. Abnormal levels of DA will lead to
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neurological disorders, like schizophrenia and Parkinson’s disease. Therefore, sensitive and selective determination of DA has an important value in clinical disease diagnosis. Different
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methods have been used for the determination of DA such as high performance liquid
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chromatography [2], fluorescence method [3], spectrophotometry [4] and electrochemical method [5]. Among these analytical methods, electrochemical method has a number of
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advantages, including simple, cost effective and high sensitivity. However, the redox potential of DA is closer to UA and its concentration is much lowered than UA in biological samples. Hence,
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the electrochemical detection of DA is quite a significant challenge. Hence, there is need to
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develop an efficient biosensor for DA determination. In this regard, highly sensitive enzyme
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based biosensors have been developed and explained their sensing mechanism [6]. The main drawback of enzyme based biosensors is the structural instability over the long time and wide
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range of temperature. Therefore, for the past few decades, as a substitute of enzyme, nanomaterials have utilized in the manufacture of highly sensitive biosensor, although these may encounter technical limits. Hence, nanofabrications [7] based on concepts such as biomimetic approaches should be developed for the next generation of microdevices. In order to develop a highly sensitive and selective DA sensor, various materials including metal oxide nanoparticles [8], conducting polymer [9], carbon based materials [10, 11], nanocomposites [12, 13] etc., have been used for the modification of electrodes. Among them, metal oxide nanoparticles, have considerable attention because of their easy synthesis, large scale production, low cost, high surface reaction activity, high catalytic efficiency and long term stability.
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Vanadium oxide (V2O5) nanoparticle is an attractive material due to its good catalytic, electrical and optical properties. The good catalytic activity is the result of easy reduction and oxidation between the multiple oxidation states of vanadium in the V2O5 [14]. It was recently
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reported that V2O5 possess electrocatalytic activity, where V5+ ions play the dominant role for the electrooxidation reaction [15]. V2O5 nanoparticles will mediate the electrochemical oxidation
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of the target molecule, while the reduced V2O4 can be continuously and simultaneously
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recovered by electrochemical oxidation due to their high surface to volume ratio. But, in contrast with interests focusing on synthetic and battery applications of V2O5, [16-18] reports on the
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electrochemical sensing property of V2O5 nanoparticles are rather rare and little attention has been paid to the detailed study of their electrochemical sensing performance. Therefore, an
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electrochemical sensing property of V2O5 nanoparticles in physiological condition may give
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benefits such as practical enzyme-free biosensor. Doping with different transition metal ions into
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V2O5 lattices will enhances the performance of existing properties [19-21]. In this view, for the first time, we have investigated the dopamine sensing of Ni-doped V2O5 nanoparticles.
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Herein, we report the preparation and dopamine sensing performance of Ni-V2O5 nanoparticles. A selective DA sensor was readily fabricated by immobilizing the prepared nanoparticles on the surface of GCE, and it was found that the Ni-V2O5/GCE showed enhanced electrocatalytic activity for the oxidation of DA compared with that of the pure V2O5 modified GCE. The sensitivity of the proposed sensor along with its improved selectivity will allow for its potential use in the diagnosis of dopamine-related disease.
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2. Experimental 2.1 Material. Ammonium metavanadate (NH4VO3), nickel sulphate (NiSO4.7H2O), oxalic acid, sodium
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dodecyl sulphate (SDS), disodium hydrogen phosphate, sodium dihydrogen phosphate and pararosaniline were purchased from Qualigens and used without further purification. Dopamine
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was purchased from Sigma-Aldrich and used as received. Doubly distilled water was used as the
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solvent thought the experiment. 2.2 Preparation of Ni-V2O5 nanoparticles
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Ni-V2O5 nanoparticles were synthesized using NH4VO3 and NiC2O4 as the V and Ni sources respectively. In order to prepare NiC2O4, 2.5 g of nickel sulphate was dissolved in 50 mL
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of 2% SDS aqueous solution. The resulting solution was heated to 70 °C under constant
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magnetic stirring. 2 M oxalic acid solution was added to the above solution under stirring
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condition which forms a precipitate. The obtained precipitate was filtered-off and dried at room temperature for 24 h. In order to prepare (x)Ni-V2O5 (x = 2-7, wt%) nanoparticles, required
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amount of NH4VO3 and NiC2O4 were taken and ground for 2 h. The resulting mixture was calcined in a muffle furnace at 450 °C for 5 h. Pure V2O5 was synthesized by following the above procedure without the addition of NiC2O4. 2.3 Instrumentation
XRD analysis were performed on Rich Siefert 3000 diffractometer with Cu-Kα1 radiation
(λ = 1.5406 Å). FT-IR analyses were conducted on Schimadzu FT-IR 8300 series instrument. Raman spectrum was recorded using laser Raman microscope, Raman-11 Nanophoton Corporation, Japan. UV-Vis absorption spectra were measured on Perkin-Elmer lambda650 spectrophotometer. The morphology and size of the samples were analyzed by FE-SEM using a
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HITACHI SU6600 field emission-scanning electron microscopy and HR-TEM analysis was carried out by FEI TECNAI G2 model T-30 at an accelerating voltage of 250 kV. The concentration of Ni was estimated by Perkin Elmer AA 700 atomic absorption spectroscopy.
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2.4. Electrochemical experiment
Cyclic voltammetry and chronoamperometry methods were utilized to examine the
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electrochemical sensing properties of Ni-doped V2O5 nanoparticles towards DA. All
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electrochemical sensing experiments were carried out using a CHI 1103A electrochemical instrument connected to a PC. The electrochemical experiments were carried out in 0.1 M
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phosphate buffer solution (PBS), pH 7.4 in a conventional three-electrode system using the bare and modified GCE as the working electrode. Platinum wire and saturated calomel electrode (SCE) were
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used as the counter electrode and reference electrode respectively. For cyclic voltammetric
measurements, the sensors were immersed in 30 mL of 0.1 M PBS containing 1×10−4 M DA,
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applying the potential in the range of -0.3 V to +1.0 V. For the chronoamperometric measurements, the sensor was immersed in the stirred PBS, applying the proper potential. When
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a stable baseline was reached, 0.2 mL of 0.1 mM DA was added successively, followed by recording the steady-state current.
All solutions used in these sensing experiments were prepared with double distilled water. All electrochemical experiments were carried out at room temperature and the potentials were referred to SCE.
Preparation of the modified electrode is as follows: The dispersion containing 1 mg of sample in 3 mL of ethanol was prepared using ultrasonication for 30 min. The highly polished GCE was coated with 5 μL of the above suspension by drop coating method. The modified GCE was activated using 0.1 M phosphate buffer solution (PBS, pH = 7.4) by successive cyclic scans
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between -0.2 and +1.0 V. Before and after each experiment, the modified GCE was washed with double distilled water and reactivated by the method mentioned above. 3. Results and discussion
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3.1 Characterization of Ni-doped V2O5
XRD patterns of Ni-V2O5 (Fig. 1A) were well resembled with orthorhombic V2O5
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(JCPDS file no. 89-0612). No characteristic peaks of Ni or nickel oxide are detected. Further, the
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diffraction peaks of Ni-doped samples are slightly shifted to lower 2θ values with broadening than the pure V2O5 (Fig. S1). Further, the calculated lattice constants are increased linearly with
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increase in Ni concentration (Table. S1). These results conclude that, Ni2+ is well doped within the V2O5 lattice because the ionic radius of Ni2+ (0.70 Å) is similar to that of V5+ (0.58 Å).
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Moreover, the average crystallite size significantly decreases by Ni doping process (Table. S1). It
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implies that the doping of Ni2+ can effectively inhibit the orthorhombic V2O5 crystalline grain
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growth and hence the decrease in intensity of the diffraction peaks was also observed [22]. Fig. 1B shows characteristic Raman pattern of orthorhombic V2O5. The band at 139 cm-1 provides an
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evidence for the layered structure of orthorhombic V2O5 [23]. Band present at 990 cm-1 corresponding to the stretching of V=O. A small shoulder band observed at 910 cm-1 corresponds to V4+-O1 stretching. Hence, the observation of V4+-O1 stretching mode confirms the presence of V4+ ion in the sample [24]. There is no Raman bands corresponding to Ni-O vibration are observed which may due to the doping of Ni into V2O5 lattice. Further, the band intensities of doped samples are remarkably lower than those of pure V2O5, which may be attributed to the low crystallinity of the doped samples [25]. This result suggested that Ni-doping might increase the disorder of the V2O5 surface and prevent the growth of the V2O5 crystallite size. It also suggests that the Ni ions may occupy the substituent sites in the V2O5 lattice as discussed in XRD
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analysis. Fig. 1C shows FTIR spectra of (x)Ni-V2O5 nanoparticles. The band at 1019 cm−1 is assigned to unshared V=O stretching vibration [26]. The band located at 836 cm−1 is characteristic of V–O–V vibrations. The band at 487 cm−1 has been attributed to the stretching
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modes of the oxygen, which are shared between three vanadium atoms. The bands observed in the range of 1030 to 450 cm-1 are all slightly shifted to higher wave number with decrease in
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intensity when compared with the bands of pure V2O5. The shift in band position with decrease
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in intensity of V-O bands are due to the presence of Ni2+ in the vicinity of oxygen and to the distortion of V=O bonds in (x)Ni-V2O5 nanoparticles. The UV-Vis absorption spectra of (x)Ni-
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V2O5 show (Fig. 1D) two intense absorption bands at 262 and 435 nm, due to the V2O5 charge-transfer bands [27]. The main absorption edge has been shifted to 501 nm, indicating that
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the substitution of Ni2+ in to the V2O5 lattices, which significantly reduced the band gap. It can
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3.2 Morphology
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be found that the 7%Ni-V2O5 has reduced band gap (Fig. S2).
The SEM images of 2%, 5%, and 7%Ni-V2O5 are shown in Fig. 2a-c. It can be seen that
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the 2% and 5%Ni-V2O5 have rod-like morphology whereas, 7%Ni-V2O5 has plate-like morphology. The rod-like particles have a diameter in the range of 20-50 nm and length upto several µm ranges. The formation of nanoplate was further confirmed by HRTEM (Fig. 2d). The well dispersed nanorods or nanoplates will have potential applications in electrochemistry due to larger available surface area. Since the morphology of the pure V2O5 and (x)Ni-V2O5 are different, the addition of Ni has significant effect on the morphology of the V2O5. Shwarsctein et al. [28] reported that the aluminum dopant significantly changes the morphology of α-Fe2O3. The EDS analysis (Fig. 2e) of 7%Ni-V2O5 shows the presence of V, Ni and O only. It shows that only 4.2% Ni present on the surface of the particles. The actual concentrations of Ni doped into
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V2O5 nanoparticles were determined by an atomic absorption spectrophotometer. The percentage of Ni in the samples is listed in Table S1. When compared with the EDS result, the concentration
on the surface but also well dispersed into the lattice of V2O5. 3.3 Electrochemical sensing of dopamine
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3.3.1 Cyclic voltammetry of DA at (x)Ni-V2O5 /GCE
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of Ni is lower on the surface of the particles than the bulk. It suggests that the Ni not only present
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The dopamine sensing property of (x)Ni-V2O5 nanoparticles modified GCE was investigated using CV in presence 1×10−4 M DA and is shown in Fig. 3A. At the (x)Ni-
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V2O5/GCE, a pair of quasi-reversible anodic and cathodic peaks caused by the redox process of DA was observed. Interestingly, for the initial scanning in the potential range of −0.3 to 1 V,
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well defined oxidation peak was observed. However from the third scan onwards, cathodic peak
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has also appeared, thus there was one pair of redox peak (Fig. 3B). This is due to the oxidation of
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dopamine into dopaminequinone [29, 30]. The irreversible process becomes quasi-reversible on continuous scan. Particularly, 7%Ni-V2O5/GCE shows enhanced anodic peak current (23.4 µA)
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with lower oxidation potential (0.4 V) at the scan rate of 100 mVs-1 than the other modified electrodes. This DA oxidation potential is less or comparable with phosphotungstic acid (PWA)– (ZnO)/Pt electrode, [31], CoHCFe film modified GCE [32], and copper dispersed sol–gel composite (Cu/SGC) electrode [33]. Results showed that the immobilized (x)Ni-V2O5 nanoparticles exhibited excellent electrocatalytic responses to DA oxidation. This enhanced electrocatalytic activity was mainly attributed to (i) the larger electroactive sites of the modifying layer due to the nanometer size of the sample. (ii) Ni-V2O5 nanoparticles are electroactive due to the presence of Ni-V5+2O5/Ni-V4+2O5 redox couple. Therefore V sites should actively involve in the electrocatalytic redox behaviour of DA. Therefore, the possible electrochemical redox
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mechanism of DA at Ni-V5+2O5/GCE can be explained by the following way: The Ni-V5+2O5 react with DA which caused electrochemical oxidation of DA and then electrochemically reduced to Ni-V4+2O5, which further donates an electron to the GCE and regenerate Ni-V5+2O5.
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The above discussed mechanism is shown below. The net reaction is compatible with previously
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reported electrochemical redox mechanism of DA.
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3.3.2 Effect of different scan rate
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251658240
Effect of potential scan rate (ν) on the electrochemical response of 1×10-4 M DA at the
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7%Ni-V2O5/GCE was investigated by CV (Fig. 4). The peak-to-peak separation (∆E) increases with increase in scan rate (ν). It can be noticed that the anodic and cathodic peak current increase simultaneously with increase in scan rates (scan rates ranged from 25 to 500 mVs−1). As in Fig. 4, the anodic peak current is more pronounced than the cathodic peak current, suggesting that the potential sweep favors electrooxidation of DA. This observed non-symmetrical redox peaks of DA in 0.1 M PBS (pH 7.0) was reported [34, 35]. The plots of both anodic and cathodic peak currents versus square root of scan rate (inset in Fig. 4) were linear, signifying a diffusioncontrolled redox process. The obtained linear regression equations are given below: Ipa (µA) = 1.5902ν1/2 (mVs-1)1/2 + 8.5116 (R2 = 0.9911)
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Ipc (µA) = -1.8232ν1/2 (mVs-1)1/2 + 10.2941 (R2 = 0.9978) 3.3.3 Determination of DA Due to its higher current sensitivity compared with CV, CA was used for the
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determination of DA. After the addition of DA into the electrochemical cell with a 7%NiV2O5/GCE as working electrode, an obvious increase of the peak current was observed (Fig. 5).
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The calibration graph for the determination of DA by the 7%Ni-V2O5/GCE is shown as an inset
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in Fig. 5. The linear range is found between of 6.6 to 62.6 µM with the corresponding regression equation I(µA) = 0.132CDA + 0.844 (R2 = 0.99). The obtained sensitivity was 132 nA/µM.
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The limit of detection (LOD) was calculated using IUPAC (International Union of Pure and Applied Chemistry) definitions,
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LOD = 3S/q
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Where S is the standard deviation and q is the slope of the calibration curve. The
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calculated LOD of 7%Ni-V2O5/GCE is found to be 28 nM. The comparison of DA determination on the proposed sensor with previously reported sensors was given in Table-1 [36-41]. The
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7%Ni-V2O5/GCE exhibits improved or comparable performance for DA determination. 3.3.4 Interference study
DA in the central nervous systems coexists with UA. The presence of electroactive UA will affect the detection of DA due to its oxidation potential which is closer to that of DA in bare electrode [42]. Therefore, we further investigate the CV and CA of 7%Ni-V2O5/GCE for the interfering substance UA. Fig. 6A and B clearly show that there is enough difference exists between the DA and UA oxidation potentials. The electrochemical oxidation of DA with different concentrations in the presence of 0.1 mM UA at 7%Ni-V2O5/GCE was studied by CA (Fig. 6C). The anodic peak current of DA increased with the different concentration of DA in
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presence of 0.1 mM UA. The experimental results showed that there was no decrease in anodic peak current. The 7%Ni-V2O5/GCE was able to determine DA even in the presence of higher concentration of UA. The obtained result indicated that the 7%Ni-V2O5/GCE possess high
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selectivity to DA. Interference studies were also carried out with other possible interfering substances. The experimental results shows that 200-fold concentration of Na+, K+, Ca2+, Mg2+,
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hardly have any influence on the determination of 1.0 µM DA.
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Cl-, nitrate, glucose, sucrose, 150 fold concentration of urea, 100-fold excess of ascorbic acid,
3.3.5 Stability, reproducibility and repeatability
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The stability of 7%Ni-V2O5/GCE was examined by CV at the scanning rate of 50 mVs-1 for 40 cycles. After each experiment, the 7%Ni-V2O5/GCE was washed in 40 mL 0.1 M PBS
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(pH 7.4) thoroughly and used for examination in next day. A gradual decrease of the anodic and
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cathodic peak currents (9.6%) was found. The reproducibility and repeatability of the present DA
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sensor is determined and the RSD of chronoamperometric current responses recorded by 10 injections of 0.1 mM DA in 0.1 M PBS is calculated to be about 3.9%.
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3.3.6 Samples analysis
In order to evaluate the analytical application of the proposed DA sensor, DPV was used for measuring the concentration of dopamine hydrochloride injection solutions. Table 2 summarizes the results obtained for the determination of DA in three independent dopamine hydrochloride injection solutions. The recovery of DA from the sample solutions was 98.7%, 98.3% and 99.7%, respectively. The results confirmed that the developed DA sensor is reliable for the determination of DA in real samples.
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4. CONCLUSION To conclude, Ni-V2O5 nanoparticles were prepared by a simple thermal decomposition method. The characterization techniques show that Ni is well doped within the lattices of V2O5.
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Further, we developed Ni-V2O5/GCE as a DA sensor by a drop coating method. The proposed Ni-V2O5/GCE exhibited high electrocatalytic activity toward DA oxidation due to the
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electroactive V5+/V4+ redox couple which was promoted by Ni2+. The 7%Ni-V2O5/GCE
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displayed wide linear range with better sensitivity in physiological condition. The easy fabrication procedure, high electrocatalytic activity and good selectivity in the presence of
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common interfering substances favor the 7%Ni-V2O5/GCE as a potential DA sensor. ACKNOWLEDGMENT
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One of the authors (RS) acknowledges the CSIR, New Delhi, India for the financial
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assistance in the form of Senior Research Fellowship. We acknowledge the FE-SEM, HR-TEM,
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University of Madras.
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and Raman facility provided by the National Centre for Nanoscience and Nanotechnology,
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26. S.Weber, R. Czerw, R. Nesper, J. DiMaio, J.F. Xu, J. Ballato, D.L. Carroll, Optical
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28. A. K. Shwarsctein, M. N. Huda, A. Walsh, Y. Yan, G. D. Stucky, Y. S. Hu, M. M. A. Jassim, E. W. McFarland, Electrodeposited Aluminum-doped α-Fe2O3 photoelectrodes: experiment
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H.E. Toma, Vanadium oxide-porphyrin nanocomposites as gas sensor interfaces for probing low water content in ethanol, Sens. Actuators B, 146 (2010) 61–68.
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30. S.Q. Liu, W.H. Sun, F.T. Hu, Graphene nano sheet-fabricated electrochemical sensor for the determination of dopamine in the presence of ascorbic acid using cetyltrimethylammonium bromide as the discriminating agent, Sens. Actuators B, 173 (2012) 497-504. 31. J. Wu, F. Yin, Studies on the electrocatalytic oxidation of dopamine at phosphotungstic acid– ZnO spun fiber-modified electrode, Sens. Actuators B, 185 (2013) 651-657. 32. S.S.L. Castro, R.J. Mortimer, M.F. de Oliveira, N.R. Stradiotto, Electrooxidation and determination of dopamine using a nafion®-cobalt hexacyanoferrate film modified electrode, Sensors, 8 (2008) 1950-1959.
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33. D. Ravi Shankaran, K. Iimura, T. Kato, Simultaneous determination of ascorbic acid and dopamine at a sol–gel composite electrode, Sens. Actuators B, 94 (2003) 73-80. 34. V.S. Vasantha, S.M. Chen, Electrocatalysis and simultaneous detection of dopamine and
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ascorbic acid using poly(3,4-ethylenedioxy)thiophene film modified electrodes, J. Electroanal. Chem., 592 (2006) 77-87.
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35. T.V. Sathisha, B.E. Kumara Swamy, Mark Schell, B. Eswarappa, Synthesis and
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characterization of carbon nanoparticles and their modified carbon paste electrode for the determination of dopamine, J. Electroanal. Chem.,720-721 (2014) 1–8.
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36. F.S. Damos, M.D.P.T. Sotomayor, L.T. Kubota, S.M.C.N. Tanaka, A.A. Tanaka, Iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin as a biomimetic catalyst of horseradish peroxidase on
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the electrode surface: an amperometric sensor for phenolic compound determinations,
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Analyst 128 (2003) 255–259.
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37. L.C. Jiang, W.D. Zhang, Electroanalysis of dopamine at RuO2 modified vertically aligned carbon nanotube electrode, Electroanalysis, 21 (2009) 1811–1815.
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38. A. Rahim, S.B.A. Barros, L.T. Kubota, Y. Gushikem, SiO2/C/Cu(II) phthalocyanine as a biomimetic catalyst for dopamine monooxygenase in the development of an amperometric sensor, Electrochim. Acta, 56 (2011) 10116–10121. 39. W. Lv, F.M. Jin, Q. Guo, Q.H. Yang, F. Kang, DNA-dispersed graphene/NiO hybrid materials for highly sensitive non-enzymatic glucose sensor, Electrochim. Acta, 73 (2012) 129-135. 40. D.X. Han, T.T. Han, C.S. Shan, A. Ivaska1, L. Niu, Simultaneous determination of ascorbic acid, dopamine and uric acid with chitosan-graphene modified electrode, Electroanalysis 22 (2010) 2001-2008.
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41. K. Min, Y.J. Yoo, Amperometric detection of dopamine based on tyrosinase–SWNTs–Ppy composite electrode, Talanta, 80 (2009) 1007-1011. 42. R.E. Sabzi, K. Rezapour, N. Samadi, Polyaniline–multi-wall-carbon nanotube
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nanocomposites as a dopamine sensor, J. Serb. Chem. Soc., 75 (2010) 537–549.
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Figure caption Fig. 1: (A) XRD patterns , (B) FTIR spectra, (C) Raman spectra and (D) DRSUV-Visible spectra of Ni doped V2O5 nanoparticles.
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Fig. 2: FE-SEM images of (a) 2%Ni-V2O5, (b) 5%Ni-V2O5, (c) 7%Ni-V2O5. (d) TEM image of 7%Ni-V2O5 and (e) EDS spectrum of 7%Ni-V2O5 nanoparticles.
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Fig. 3: Cyclic voltammograms of (a) bare GCE, (b) V2O5/GCE, (c) 2%Ni-V2O5/GCE, (d) 5%NiV2O5/GCE, and (e) 7%Ni-V2O5/GCE in presence of 1×10-4 M DA at scan rate of 50 mVs-1 (A) and 100 mVs-1 (B).
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Fig. 4: Cyclic voltammograms of 7%Ni-V2O5/GCE in 1×10-4 M DA (pH = 7.4) at the scan rate of (a) 50, (b) 70, (c) 100, (d) 150, (e) 200, (f) 250, (g) 300, (h) 350, (i) 400, (j) 450 and (k) 500 mVs-1. Inset Figure: (A) The linear relationship between anodic current (Ipa) versus scan rate. (B) Plot of square root of scan rate versus Ipa.
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Fig. 5: Chronoamperometric responses of 7%Ni-V2O5/GCE for the successive additions of 0.2 mL of 1×10-4 M DA to 30 mL of 0.1 M PBS. Applied potential is 0.4 V. Inset is the plot of current versus concentration of UA.
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Fig. 6: (A) Cyclic voltammograms of 0.1 mM M DA and 0.1 mM UA at 7%Ni-V2O5/GCE. (B) Chronoamperometric responses of 7%Ni-V2O5/GCE for the successive additions of 0.2 mL of (a, b) 0.1 mM DA and (c, d) 0.1 mM UA to 30 mL of 0.1 M PBS. Applied potential for DA and UA is 0.4 V and 0.55 V respectively. (C) Chronoamperometric response of 7%Ni-V2O5/GCE for the successive additions of 0.2 mL of 0.1 mM DA in presence of 0.1 mM UA.
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Table – 1: Comparison of the analytical performance of the proposed dopamine sensor with
Sensitivity
Reference
0.6–6.0
0.061 nA µM-1
[36]
RuO2/MWNT
0.6–360
0.084 nA µM-1
[37]
SiO2/C/CuPc
10–140
0.630 nA µM-1
[38]
GNS/NiO/DNA
1 µM–8 mM
9.0 nA mM-1
[39]
1 –200 1-24
Tyr-SWNTs–Ppy
5.0 –50.0
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Chitosan-graphene
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FeIIIT4MpyP-His
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Linear range (µM)
6.6 - 62.6
-1
-
[40]
-
[41]
132 nA µM-1
This work
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7%Ni-V2O5/GCE
14.3 nA mM
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Sensor
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previously reported dopamine sensors.
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FeIIIT4MpyP-His: iron tetra-(N-methyl-4-pyridyl)porphyrin-histidine.
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MWNT: multiwalled carbon nanotubes. C: carbon, CuPc: Cu(II) phthalocyanine GNS: graphene nanosheet, Tyr: tyrosinase, SWNTs: single walled carbon nanotubes Ppy: polypyrrole, GCE: glassy carbon electrode.
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Added
Found
Recovery
(µM)
(µM)
(µM)
(%)
I
12.1
25.0
36.6
98.7
II
13.6
25.0
37.8
III
11.7
25.0
36.6
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Detected
98.3
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99.7
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Samples
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Table - 2 Results of determination of DA in dopamine hydrochloride injections
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Research highlights Ni-doped V2O5 nanoparticles have been prepared by thermal decomposition method.
Possible dopamine sensing mechanism has been proposed.
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Ni-doped V2O5 exhibits highly sensitive and selective dopamine sensing property.
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Ni-V2O5 sensor shows good linear range, reproducibility, repeatability and stability.
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Biography R. Suresh is a Ph.D., student in Dr. V. Narayanan Group, working on the electrochemical sensor and photocatalysis based on metal oxide nanoparticles. He has received M.Sc., from the Department of Inorganic Chemistry, University of Madras, India.
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K. Giribabu is a Ph.D., student in Dr. V. Narayanan Group, working on graphene based nanocomposites. His research interest is mainly on environmental sensor and photocatalysis. He has received M.Sc., from Department of Analytical Chemistry, University of Madras, India.
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R. Manigandan is a Ph.D., student in Dr. V. Narayanan Group, working on d- and fblock metal oxide nanoparticles. He has received M.Sc., from Department of Physical Chemistry, University of Madras, India.
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S. Praveen Kumar is a Ph.D., student in Dr. V. Narayanan Group. His research interest is bioinorganic chemistry and he is working on the electrochemical sensor based on metal complexes. He has received M.Sc., from Department of Chemistry, Annamalai University, India.
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S. Munusamy is a Ph.D., student in Dr. V. Narayanan Group, working conducting polymer based nanocomposites. He has received M.Sc., from Department of Inorganic Chemistry, University of Madras, India
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S. Muthamizh is a Ph.D., student in Dr. V. Narayanan Group, working on metal tungstates and molybdates nanoparticles. She has received M.Sc., from Department of Chemistry, Thiruvalluvar University, India
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Dr. A. Stephen is an Assistant Professor, Department of Nuclear Physics, University of Madras, India. He is a physicist and his group is working in the field of materials science.
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Dr. V. Narayanan is an Assistant Professor, Department of Inorganic Chemistry, University of Madras, India. He has published more than 120 research papers and 8 books. His group is working in the field of bioinorganic chemistry and materials chemistry.
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Graphical Abstract (for review)
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S0925-4005(14)00634-0 http://dx.doi.org/doi:10.1016/j.snb.2014.05.095 SNB 16969
To appear in:
Sensors and Actuators B
Received date: Revised date: Accepted date:
28-2-2014 13-5-2014 22-5-2014
Please cite this article as: R. Suresh, K. Giribabu, R. Manigandan, S.P. Kumar, S. Munusamy, S. Muthamizh, A. Stephen, V. Narayanan, New electrochemical sensor based on Ni-doped V2 O5 nanoplates modified glassy carbon electrode for selective determination of dopamine at nanomolar level, Sensors and Actuators B: Chemical (2014), http://dx.doi.org/10.1016/j.snb.2014.05.095 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.
1
New electrochemical sensor based on Ni-doped V2O5 nanoplates modified glassy carbon electrode for selective determination of dopamine at
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nanomolar level R. Suresh1, K. Giribabu1, R. Manigandan1, S. Praveen Kumar1, S. Munusamy1, S. Muthamizh1, A. Stephen2, and V. Narayanan1*
Department of Inorganic Chemistry, University of Madras, Guindy Maraimalai Campus,
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Chennai 600 025, India.
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1
Department of Nuclear Physics, University of Madras, Guindy Maraimalai Campus, Chennai
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600 025, India
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Address for Correspondence*
Assistant Professor, School of Chemical Sciences,
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Department of Inorganic Chemistry,
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Dr. V. Narayanan,
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University of Madras, Guindy Maraimalai Campus, Chennai 600 025, Tamil Nadu, India. Phone: 91 44 22202793; Fax: 91 44 22300488. Email: [email protected] (V. Narayanan).
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Abstract Ni-doped(0, 2, 5 and 7 wt%)V2O5 nanoparticles were prepared by thermal decomposition method. The as-prepared nanoparticles are characterized by X-ray diffraction (XRD), Fourier infrared
spectroscopy
(FTIR), Raman spectroscopy, UV-Vis absorption
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transformed
spectroscopy, scanning electron microscopy (SEM) and high resolution-transmission electron
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microscopy (HR-TEM). The results indicated that the Ni2+ ions are well doped within V2O5
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lattices. Compared with pure V2O5, Ni-doped V2O5 (Ni-V2O5) nanoparticles exhibit enhanced dopamine (DA) sensing property. Particularly, 7%Ni-V2O5 nanoplates modified glassy carbon
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electrode (7%Ni-V2O5/GCE) showed a good response to the DA concentration in the range of 6.6 to 96.4 µM with sensitivity of 132 nAµM-1. The obtained limit of detection (LOD) is 28 nM
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(S/N = 3). A possible mechanism related to the electrochemical oxidation of DA was proposed.
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Further, the proposed method was successfully utilized to determine DA in dopamine
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hydrochloride solution (11 to 13 µM) and reasonable results were obtained. The results showed that the exhibits an excellent electrocatalytic activity, good sensitivity, reproducibility,
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repeatability and long-term stability.
Keywords: Ni-doped V2O5, thermal decomposition, nanoplates, dopamine, modified electrode
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1 Introduction Dopamine (DA) is an electroactive neurotransmitter and plays a vital role in the function of the central nervous system in mammalian [1]. Abnormal levels of DA will lead to
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neurological disorders, like schizophrenia and Parkinson’s disease. Therefore, sensitive and selective determination of DA has an important value in clinical disease diagnosis. Different
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methods have been used for the determination of DA such as high performance liquid
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chromatography [2], fluorescence method [3], spectrophotometry [4] and electrochemical method [5]. Among these analytical methods, electrochemical method has a number of
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advantages, including simple, cost effective and high sensitivity. However, the redox potential of DA is closer to UA and its concentration is much lowered than UA in biological samples. Hence,
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the electrochemical detection of DA is quite a significant challenge. Hence, there is need to
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develop an efficient biosensor for DA determination. In this regard, highly sensitive enzyme
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based biosensors have been developed and explained their sensing mechanism [6]. The main drawback of enzyme based biosensors is the structural instability over the long time and wide
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range of temperature. Therefore, for the past few decades, as a substitute of enzyme, nanomaterials have utilized in the manufacture of highly sensitive biosensor, although these may encounter technical limits. Hence, nanofabrications [7] based on concepts such as biomimetic approaches should be developed for the next generation of microdevices. In order to develop a highly sensitive and selective DA sensor, various materials including metal oxide nanoparticles [8], conducting polymer [9], carbon based materials [10, 11], nanocomposites [12, 13] etc., have been used for the modification of electrodes. Among them, metal oxide nanoparticles, have considerable attention because of their easy synthesis, large scale production, low cost, high surface reaction activity, high catalytic efficiency and long term stability.
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Vanadium oxide (V2O5) nanoparticle is an attractive material due to its good catalytic, electrical and optical properties. The good catalytic activity is the result of easy reduction and oxidation between the multiple oxidation states of vanadium in the V2O5 [14]. It was recently
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reported that V2O5 possess electrocatalytic activity, where V5+ ions play the dominant role for the electrooxidation reaction [15]. V2O5 nanoparticles will mediate the electrochemical oxidation
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of the target molecule, while the reduced V2O4 can be continuously and simultaneously
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recovered by electrochemical oxidation due to their high surface to volume ratio. But, in contrast with interests focusing on synthetic and battery applications of V2O5, [16-18] reports on the
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electrochemical sensing property of V2O5 nanoparticles are rather rare and little attention has been paid to the detailed study of their electrochemical sensing performance. Therefore, an
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electrochemical sensing property of V2O5 nanoparticles in physiological condition may give
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benefits such as practical enzyme-free biosensor. Doping with different transition metal ions into
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V2O5 lattices will enhances the performance of existing properties [19-21]. In this view, for the first time, we have investigated the dopamine sensing of Ni-doped V2O5 nanoparticles.
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Herein, we report the preparation and dopamine sensing performance of Ni-V2O5 nanoparticles. A selective DA sensor was readily fabricated by immobilizing the prepared nanoparticles on the surface of GCE, and it was found that the Ni-V2O5/GCE showed enhanced electrocatalytic activity for the oxidation of DA compared with that of the pure V2O5 modified GCE. The sensitivity of the proposed sensor along with its improved selectivity will allow for its potential use in the diagnosis of dopamine-related disease.
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2. Experimental 2.1 Material. Ammonium metavanadate (NH4VO3), nickel sulphate (NiSO4.7H2O), oxalic acid, sodium
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dodecyl sulphate (SDS), disodium hydrogen phosphate, sodium dihydrogen phosphate and pararosaniline were purchased from Qualigens and used without further purification. Dopamine
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was purchased from Sigma-Aldrich and used as received. Doubly distilled water was used as the
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solvent thought the experiment. 2.2 Preparation of Ni-V2O5 nanoparticles
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Ni-V2O5 nanoparticles were synthesized using NH4VO3 and NiC2O4 as the V and Ni sources respectively. In order to prepare NiC2O4, 2.5 g of nickel sulphate was dissolved in 50 mL
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of 2% SDS aqueous solution. The resulting solution was heated to 70 °C under constant
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magnetic stirring. 2 M oxalic acid solution was added to the above solution under stirring
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condition which forms a precipitate. The obtained precipitate was filtered-off and dried at room temperature for 24 h. In order to prepare (x)Ni-V2O5 (x = 2-7, wt%) nanoparticles, required
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amount of NH4VO3 and NiC2O4 were taken and ground for 2 h. The resulting mixture was calcined in a muffle furnace at 450 °C for 5 h. Pure V2O5 was synthesized by following the above procedure without the addition of NiC2O4. 2.3 Instrumentation
XRD analysis were performed on Rich Siefert 3000 diffractometer with Cu-Kα1 radiation
(λ = 1.5406 Å). FT-IR analyses were conducted on Schimadzu FT-IR 8300 series instrument. Raman spectrum was recorded using laser Raman microscope, Raman-11 Nanophoton Corporation, Japan. UV-Vis absorption spectra were measured on Perkin-Elmer lambda650 spectrophotometer. The morphology and size of the samples were analyzed by FE-SEM using a
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HITACHI SU6600 field emission-scanning electron microscopy and HR-TEM analysis was carried out by FEI TECNAI G2 model T-30 at an accelerating voltage of 250 kV. The concentration of Ni was estimated by Perkin Elmer AA 700 atomic absorption spectroscopy.
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2.4. Electrochemical experiment
Cyclic voltammetry and chronoamperometry methods were utilized to examine the
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electrochemical sensing properties of Ni-doped V2O5 nanoparticles towards DA. All
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electrochemical sensing experiments were carried out using a CHI 1103A electrochemical instrument connected to a PC. The electrochemical experiments were carried out in 0.1 M
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phosphate buffer solution (PBS), pH 7.4 in a conventional three-electrode system using the bare and modified GCE as the working electrode. Platinum wire and saturated calomel electrode (SCE) were
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used as the counter electrode and reference electrode respectively. For cyclic voltammetric
measurements, the sensors were immersed in 30 mL of 0.1 M PBS containing 1×10−4 M DA,
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applying the potential in the range of -0.3 V to +1.0 V. For the chronoamperometric measurements, the sensor was immersed in the stirred PBS, applying the proper potential. When
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a stable baseline was reached, 0.2 mL of 0.1 mM DA was added successively, followed by recording the steady-state current.
All solutions used in these sensing experiments were prepared with double distilled water. All electrochemical experiments were carried out at room temperature and the potentials were referred to SCE.
Preparation of the modified electrode is as follows: The dispersion containing 1 mg of sample in 3 mL of ethanol was prepared using ultrasonication for 30 min. The highly polished GCE was coated with 5 μL of the above suspension by drop coating method. The modified GCE was activated using 0.1 M phosphate buffer solution (PBS, pH = 7.4) by successive cyclic scans
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between -0.2 and +1.0 V. Before and after each experiment, the modified GCE was washed with double distilled water and reactivated by the method mentioned above. 3. Results and discussion
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3.1 Characterization of Ni-doped V2O5
XRD patterns of Ni-V2O5 (Fig. 1A) were well resembled with orthorhombic V2O5
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(JCPDS file no. 89-0612). No characteristic peaks of Ni or nickel oxide are detected. Further, the
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diffraction peaks of Ni-doped samples are slightly shifted to lower 2θ values with broadening than the pure V2O5 (Fig. S1). Further, the calculated lattice constants are increased linearly with
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increase in Ni concentration (Table. S1). These results conclude that, Ni2+ is well doped within the V2O5 lattice because the ionic radius of Ni2+ (0.70 Å) is similar to that of V5+ (0.58 Å).
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Moreover, the average crystallite size significantly decreases by Ni doping process (Table. S1). It
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implies that the doping of Ni2+ can effectively inhibit the orthorhombic V2O5 crystalline grain
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growth and hence the decrease in intensity of the diffraction peaks was also observed [22]. Fig. 1B shows characteristic Raman pattern of orthorhombic V2O5. The band at 139 cm-1 provides an
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evidence for the layered structure of orthorhombic V2O5 [23]. Band present at 990 cm-1 corresponding to the stretching of V=O. A small shoulder band observed at 910 cm-1 corresponds to V4+-O1 stretching. Hence, the observation of V4+-O1 stretching mode confirms the presence of V4+ ion in the sample [24]. There is no Raman bands corresponding to Ni-O vibration are observed which may due to the doping of Ni into V2O5 lattice. Further, the band intensities of doped samples are remarkably lower than those of pure V2O5, which may be attributed to the low crystallinity of the doped samples [25]. This result suggested that Ni-doping might increase the disorder of the V2O5 surface and prevent the growth of the V2O5 crystallite size. It also suggests that the Ni ions may occupy the substituent sites in the V2O5 lattice as discussed in XRD
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analysis. Fig. 1C shows FTIR spectra of (x)Ni-V2O5 nanoparticles. The band at 1019 cm−1 is assigned to unshared V=O stretching vibration [26]. The band located at 836 cm−1 is characteristic of V–O–V vibrations. The band at 487 cm−1 has been attributed to the stretching
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modes of the oxygen, which are shared between three vanadium atoms. The bands observed in the range of 1030 to 450 cm-1 are all slightly shifted to higher wave number with decrease in
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intensity when compared with the bands of pure V2O5. The shift in band position with decrease
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in intensity of V-O bands are due to the presence of Ni2+ in the vicinity of oxygen and to the distortion of V=O bonds in (x)Ni-V2O5 nanoparticles. The UV-Vis absorption spectra of (x)Ni-
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V2O5 show (Fig. 1D) two intense absorption bands at 262 and 435 nm, due to the V2O5 charge-transfer bands [27]. The main absorption edge has been shifted to 501 nm, indicating that
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the substitution of Ni2+ in to the V2O5 lattices, which significantly reduced the band gap. It can
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3.2 Morphology
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be found that the 7%Ni-V2O5 has reduced band gap (Fig. S2).
The SEM images of 2%, 5%, and 7%Ni-V2O5 are shown in Fig. 2a-c. It can be seen that
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the 2% and 5%Ni-V2O5 have rod-like morphology whereas, 7%Ni-V2O5 has plate-like morphology. The rod-like particles have a diameter in the range of 20-50 nm and length upto several µm ranges. The formation of nanoplate was further confirmed by HRTEM (Fig. 2d). The well dispersed nanorods or nanoplates will have potential applications in electrochemistry due to larger available surface area. Since the morphology of the pure V2O5 and (x)Ni-V2O5 are different, the addition of Ni has significant effect on the morphology of the V2O5. Shwarsctein et al. [28] reported that the aluminum dopant significantly changes the morphology of α-Fe2O3. The EDS analysis (Fig. 2e) of 7%Ni-V2O5 shows the presence of V, Ni and O only. It shows that only 4.2% Ni present on the surface of the particles. The actual concentrations of Ni doped into
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V2O5 nanoparticles were determined by an atomic absorption spectrophotometer. The percentage of Ni in the samples is listed in Table S1. When compared with the EDS result, the concentration
on the surface but also well dispersed into the lattice of V2O5. 3.3 Electrochemical sensing of dopamine
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3.3.1 Cyclic voltammetry of DA at (x)Ni-V2O5 /GCE
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of Ni is lower on the surface of the particles than the bulk. It suggests that the Ni not only present
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The dopamine sensing property of (x)Ni-V2O5 nanoparticles modified GCE was investigated using CV in presence 1×10−4 M DA and is shown in Fig. 3A. At the (x)Ni-
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V2O5/GCE, a pair of quasi-reversible anodic and cathodic peaks caused by the redox process of DA was observed. Interestingly, for the initial scanning in the potential range of −0.3 to 1 V,
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well defined oxidation peak was observed. However from the third scan onwards, cathodic peak
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has also appeared, thus there was one pair of redox peak (Fig. 3B). This is due to the oxidation of
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dopamine into dopaminequinone [29, 30]. The irreversible process becomes quasi-reversible on continuous scan. Particularly, 7%Ni-V2O5/GCE shows enhanced anodic peak current (23.4 µA)
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with lower oxidation potential (0.4 V) at the scan rate of 100 mVs-1 than the other modified electrodes. This DA oxidation potential is less or comparable with phosphotungstic acid (PWA)– (ZnO)/Pt electrode, [31], CoHCFe film modified GCE [32], and copper dispersed sol–gel composite (Cu/SGC) electrode [33]. Results showed that the immobilized (x)Ni-V2O5 nanoparticles exhibited excellent electrocatalytic responses to DA oxidation. This enhanced electrocatalytic activity was mainly attributed to (i) the larger electroactive sites of the modifying layer due to the nanometer size of the sample. (ii) Ni-V2O5 nanoparticles are electroactive due to the presence of Ni-V5+2O5/Ni-V4+2O5 redox couple. Therefore V sites should actively involve in the electrocatalytic redox behaviour of DA. Therefore, the possible electrochemical redox
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mechanism of DA at Ni-V5+2O5/GCE can be explained by the following way: The Ni-V5+2O5 react with DA which caused electrochemical oxidation of DA and then electrochemically reduced to Ni-V4+2O5, which further donates an electron to the GCE and regenerate Ni-V5+2O5.
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The above discussed mechanism is shown below. The net reaction is compatible with previously
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reported electrochemical redox mechanism of DA.
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3.3.2 Effect of different scan rate
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Effect of potential scan rate (ν) on the electrochemical response of 1×10-4 M DA at the
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7%Ni-V2O5/GCE was investigated by CV (Fig. 4). The peak-to-peak separation (∆E) increases with increase in scan rate (ν). It can be noticed that the anodic and cathodic peak current increase simultaneously with increase in scan rates (scan rates ranged from 25 to 500 mVs−1). As in Fig. 4, the anodic peak current is more pronounced than the cathodic peak current, suggesting that the potential sweep favors electrooxidation of DA. This observed non-symmetrical redox peaks of DA in 0.1 M PBS (pH 7.0) was reported [34, 35]. The plots of both anodic and cathodic peak currents versus square root of scan rate (inset in Fig. 4) were linear, signifying a diffusioncontrolled redox process. The obtained linear regression equations are given below: Ipa (µA) = 1.5902ν1/2 (mVs-1)1/2 + 8.5116 (R2 = 0.9911)
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Ipc (µA) = -1.8232ν1/2 (mVs-1)1/2 + 10.2941 (R2 = 0.9978) 3.3.3 Determination of DA Due to its higher current sensitivity compared with CV, CA was used for the
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determination of DA. After the addition of DA into the electrochemical cell with a 7%NiV2O5/GCE as working electrode, an obvious increase of the peak current was observed (Fig. 5).
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The calibration graph for the determination of DA by the 7%Ni-V2O5/GCE is shown as an inset
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in Fig. 5. The linear range is found between of 6.6 to 62.6 µM with the corresponding regression equation I(µA) = 0.132CDA + 0.844 (R2 = 0.99). The obtained sensitivity was 132 nA/µM.
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The limit of detection (LOD) was calculated using IUPAC (International Union of Pure and Applied Chemistry) definitions,
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LOD = 3S/q
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Where S is the standard deviation and q is the slope of the calibration curve. The
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calculated LOD of 7%Ni-V2O5/GCE is found to be 28 nM. The comparison of DA determination on the proposed sensor with previously reported sensors was given in Table-1 [36-41]. The
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7%Ni-V2O5/GCE exhibits improved or comparable performance for DA determination. 3.3.4 Interference study
DA in the central nervous systems coexists with UA. The presence of electroactive UA will affect the detection of DA due to its oxidation potential which is closer to that of DA in bare electrode [42]. Therefore, we further investigate the CV and CA of 7%Ni-V2O5/GCE for the interfering substance UA. Fig. 6A and B clearly show that there is enough difference exists between the DA and UA oxidation potentials. The electrochemical oxidation of DA with different concentrations in the presence of 0.1 mM UA at 7%Ni-V2O5/GCE was studied by CA (Fig. 6C). The anodic peak current of DA increased with the different concentration of DA in
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presence of 0.1 mM UA. The experimental results showed that there was no decrease in anodic peak current. The 7%Ni-V2O5/GCE was able to determine DA even in the presence of higher concentration of UA. The obtained result indicated that the 7%Ni-V2O5/GCE possess high
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selectivity to DA. Interference studies were also carried out with other possible interfering substances. The experimental results shows that 200-fold concentration of Na+, K+, Ca2+, Mg2+,
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hardly have any influence on the determination of 1.0 µM DA.
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Cl-, nitrate, glucose, sucrose, 150 fold concentration of urea, 100-fold excess of ascorbic acid,
3.3.5 Stability, reproducibility and repeatability
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The stability of 7%Ni-V2O5/GCE was examined by CV at the scanning rate of 50 mVs-1 for 40 cycles. After each experiment, the 7%Ni-V2O5/GCE was washed in 40 mL 0.1 M PBS
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(pH 7.4) thoroughly and used for examination in next day. A gradual decrease of the anodic and
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cathodic peak currents (9.6%) was found. The reproducibility and repeatability of the present DA
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sensor is determined and the RSD of chronoamperometric current responses recorded by 10 injections of 0.1 mM DA in 0.1 M PBS is calculated to be about 3.9%.
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3.3.6 Samples analysis
In order to evaluate the analytical application of the proposed DA sensor, DPV was used for measuring the concentration of dopamine hydrochloride injection solutions. Table 2 summarizes the results obtained for the determination of DA in three independent dopamine hydrochloride injection solutions. The recovery of DA from the sample solutions was 98.7%, 98.3% and 99.7%, respectively. The results confirmed that the developed DA sensor is reliable for the determination of DA in real samples.
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4. CONCLUSION To conclude, Ni-V2O5 nanoparticles were prepared by a simple thermal decomposition method. The characterization techniques show that Ni is well doped within the lattices of V2O5.
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Further, we developed Ni-V2O5/GCE as a DA sensor by a drop coating method. The proposed Ni-V2O5/GCE exhibited high electrocatalytic activity toward DA oxidation due to the
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electroactive V5+/V4+ redox couple which was promoted by Ni2+. The 7%Ni-V2O5/GCE
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displayed wide linear range with better sensitivity in physiological condition. The easy fabrication procedure, high electrocatalytic activity and good selectivity in the presence of
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common interfering substances favor the 7%Ni-V2O5/GCE as a potential DA sensor. ACKNOWLEDGMENT
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One of the authors (RS) acknowledges the CSIR, New Delhi, India for the financial
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assistance in the form of Senior Research Fellowship. We acknowledge the FE-SEM, HR-TEM,
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University of Madras.
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and Raman facility provided by the National Centre for Nanoscience and Nanotechnology,
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41. K. Min, Y.J. Yoo, Amperometric detection of dopamine based on tyrosinase–SWNTs–Ppy composite electrode, Talanta, 80 (2009) 1007-1011. 42. R.E. Sabzi, K. Rezapour, N. Samadi, Polyaniline–multi-wall-carbon nanotube
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Figure caption Fig. 1: (A) XRD patterns , (B) FTIR spectra, (C) Raman spectra and (D) DRSUV-Visible spectra of Ni doped V2O5 nanoparticles.
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Fig. 2: FE-SEM images of (a) 2%Ni-V2O5, (b) 5%Ni-V2O5, (c) 7%Ni-V2O5. (d) TEM image of 7%Ni-V2O5 and (e) EDS spectrum of 7%Ni-V2O5 nanoparticles.
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Fig. 3: Cyclic voltammograms of (a) bare GCE, (b) V2O5/GCE, (c) 2%Ni-V2O5/GCE, (d) 5%NiV2O5/GCE, and (e) 7%Ni-V2O5/GCE in presence of 1×10-4 M DA at scan rate of 50 mVs-1 (A) and 100 mVs-1 (B).
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Fig. 4: Cyclic voltammograms of 7%Ni-V2O5/GCE in 1×10-4 M DA (pH = 7.4) at the scan rate of (a) 50, (b) 70, (c) 100, (d) 150, (e) 200, (f) 250, (g) 300, (h) 350, (i) 400, (j) 450 and (k) 500 mVs-1. Inset Figure: (A) The linear relationship between anodic current (Ipa) versus scan rate. (B) Plot of square root of scan rate versus Ipa.
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Fig. 5: Chronoamperometric responses of 7%Ni-V2O5/GCE for the successive additions of 0.2 mL of 1×10-4 M DA to 30 mL of 0.1 M PBS. Applied potential is 0.4 V. Inset is the plot of current versus concentration of UA.
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Fig. 6: (A) Cyclic voltammograms of 0.1 mM M DA and 0.1 mM UA at 7%Ni-V2O5/GCE. (B) Chronoamperometric responses of 7%Ni-V2O5/GCE for the successive additions of 0.2 mL of (a, b) 0.1 mM DA and (c, d) 0.1 mM UA to 30 mL of 0.1 M PBS. Applied potential for DA and UA is 0.4 V and 0.55 V respectively. (C) Chronoamperometric response of 7%Ni-V2O5/GCE for the successive additions of 0.2 mL of 0.1 mM DA in presence of 0.1 mM UA.
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Table – 1: Comparison of the analytical performance of the proposed dopamine sensor with
Sensitivity
Reference
0.6–6.0
0.061 nA µM-1
[36]
RuO2/MWNT
0.6–360
0.084 nA µM-1
[37]
SiO2/C/CuPc
10–140
0.630 nA µM-1
[38]
GNS/NiO/DNA
1 µM–8 mM
9.0 nA mM-1
[39]
1 –200 1-24
Tyr-SWNTs–Ppy
5.0 –50.0
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Chitosan-graphene
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FeIIIT4MpyP-His
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Linear range (µM)
6.6 - 62.6
-1
-
[40]
-
[41]
132 nA µM-1
This work
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7%Ni-V2O5/GCE
14.3 nA mM
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Sensor
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previously reported dopamine sensors.
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FeIIIT4MpyP-His: iron tetra-(N-methyl-4-pyridyl)porphyrin-histidine.
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MWNT: multiwalled carbon nanotubes. C: carbon, CuPc: Cu(II) phthalocyanine GNS: graphene nanosheet, Tyr: tyrosinase, SWNTs: single walled carbon nanotubes Ppy: polypyrrole, GCE: glassy carbon electrode.
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Added
Found
Recovery
(µM)
(µM)
(µM)
(%)
I
12.1
25.0
36.6
98.7
II
13.6
25.0
37.8
III
11.7
25.0
36.6
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Detected
98.3
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99.7
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Table - 2 Results of determination of DA in dopamine hydrochloride injections
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Research highlights Ni-doped V2O5 nanoparticles have been prepared by thermal decomposition method.
Possible dopamine sensing mechanism has been proposed.
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Ni-doped V2O5 exhibits highly sensitive and selective dopamine sensing property.
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Ni-V2O5 sensor shows good linear range, reproducibility, repeatability and stability.
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Biography R. Suresh is a Ph.D., student in Dr. V. Narayanan Group, working on the electrochemical sensor and photocatalysis based on metal oxide nanoparticles. He has received M.Sc., from the Department of Inorganic Chemistry, University of Madras, India.
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K. Giribabu is a Ph.D., student in Dr. V. Narayanan Group, working on graphene based nanocomposites. His research interest is mainly on environmental sensor and photocatalysis. He has received M.Sc., from Department of Analytical Chemistry, University of Madras, India.
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R. Manigandan is a Ph.D., student in Dr. V. Narayanan Group, working on d- and fblock metal oxide nanoparticles. He has received M.Sc., from Department of Physical Chemistry, University of Madras, India.
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S. Praveen Kumar is a Ph.D., student in Dr. V. Narayanan Group. His research interest is bioinorganic chemistry and he is working on the electrochemical sensor based on metal complexes. He has received M.Sc., from Department of Chemistry, Annamalai University, India.
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S. Munusamy is a Ph.D., student in Dr. V. Narayanan Group, working conducting polymer based nanocomposites. He has received M.Sc., from Department of Inorganic Chemistry, University of Madras, India
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S. Muthamizh is a Ph.D., student in Dr. V. Narayanan Group, working on metal tungstates and molybdates nanoparticles. She has received M.Sc., from Department of Chemistry, Thiruvalluvar University, India
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Dr. A. Stephen is an Assistant Professor, Department of Nuclear Physics, University of Madras, India. He is a physicist and his group is working in the field of materials science.
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Dr. V. Narayanan is an Assistant Professor, Department of Inorganic Chemistry, University of Madras, India. He has published more than 120 research papers and 8 books. His group is working in the field of bioinorganic chemistry and materials chemistry.
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Graphical Abstract (for review)
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