A glassy carbon electrode modified with a copper

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magnetic nanoparticles for the extraction of flavonoids from tea, wine and urine ... rutin, quercetin, and adenosine in flos carthami by capillary elec- trophoresis.
Microchimica Acta425:81) 02( https://doi.org/10.1007/s00604-018-3071-4

ORIGINAL PAPER

A glassy carbon electrode modified with a copper tungstate and polyaniline nanocomposite for voltammetric determination of quercetin Sathish Kumar Ponnaiah 1 & Prakash Periakaruppan 1 Received: 25 July 2018 / Accepted: 24 October 2018 # Springer-Verlag GmbH Austria, part of Springer Nature 2018

Abstract A binary nanocomposite of type copper tungstate and polyaniline (CuWO4@PANI) is described that was obtained by single step polymerization on the surface of a glassy carbon electrode (GCE). The resulting electrode is shown to be a viable tool for voltammetric sensing of quercetin (Qn) in blood, urine and certain food samples. The nanocomposite was characterized by UVvisible absorption spectroscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction and highresolution transmission electron microscopy. Differential pulse voltammetry was applied to quantify Qn, typically at the relatively low working potential of 0.15 V (vs. Ag/AgCl). The modified GCE has a wide analytical range (0.001–0.500 μM) and a low detection limit (1.2 nM). The sensor is reproducible, selective and stable. This makes it suitable for determination of Qn in real samples without complicated sample pretreatment. Keywords Copper tungstate/polyaniline . Nanocomposite . Electrochemical sensor . Quercetin . Differential pulse voltammetry

Introduction In biochemistry, clinical medicine, natural pharmaceutical chemistry and nutrition science, the appropriate level of The analytical quantitation of quercetin (Qn) is important in areas such as biochemistry, clinical medicine, natural pharmaceutical chemistry and nutrition science [1–4]. An excess intake of Qn may lead to headache, kidney cancer and stomach upset. Glutathione S-transferase activity is decreased by an overdose of Qn, and this can cause DNA damage. In the absence of long-standing safety data, generally it is not advisable for pregnant women and breast-feeding mothers to take Qn.Though various analytical techniques have been advanced hitherto to detect Qn including capillary electrophoresis [5],

Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00604-018-3071-4) contains supplementary material, which is available to authorized users. * Prakash Periakaruppan [email protected]; [email protected] 1

Department of Chemistry, Thiagarajar College, Madurai, Tamil Nadu 625 009, India

fluorescence [6], high performance liquid chromatography [7], and spectrophotometry [8], the electrochemical techniques are proven to be better for the determination of Qn due the benefits accrued which include accuracy, credibility, high sensitivity and selectivity, rapid response and simplicity [9, 10]. Yet here also, the bare electrodes show less electrochemical activity, poor sensitivity and reproducibility [11]. Consequently, in order to improve the electro-sensing performance, considerable attention is focused on the modification of bare electrodes. One of such modifications use transition metal oxides based nanocomposites [10]. Metal oxides such as Fe2O3, WO3 and TiO2 have long been studied for electrochemical sensing. But again the main drawback associated with metal oxides is poor stability during sensing process [2, 10]. Hence it is imperative to design and develop a nanocomposite with high surface area, long-term stability, high electrocatalytic activity, and reusability, which should be able to promote the kinetics of electron transfer reactions. These features are able to be achieved using CuWO4 which has been used hitherto in photo catalytic applications. Moreover it is in vogue that the sensitivity and selectivity of the electrode materials are boosted by doping metal oxides with conducting polymers [12–15]. Among them, polyaniline (PANI) has received much attention due to its low cost, unique redox

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behavior, good environmental and chemical stability, relatively high conductivity and ease of blending with other materials [16–18]. The present manuscript reports the synthesis of CuWO4/PANI nanocomposite by chemical oxidative one step polymerization. The prepared material was characterized by UV-Vis, FT-IR, TGA, XRD and HR-TEM analysis. The fabricated nanocomposite material was applied for the construction of Qn sensor which shows extensive detection range, good performance, high selectivity and fast detection.

Experimental section Reagents and materials Ammonium persulfate ((NH4)2S2O8), aniline (C6H5NH2), copper nitrate trihydrate (Cu(NO3)2.3H2O), polyethylene glycol (PEG) (C 2nH4n + 2On + 1), polyvinyl pyrrolidone (C6H9NO)n, and Sodium tungstate dihydrate (Na 2 WO 4 .2H 2 O) were procured from Sigma-Aldrich

Scheme 1 Synthesis of CuWO4@PANI nanocomposite and the possible mechanism of oxidation and reduction reaction of the quercetin

(www.sigma-aldrich.com). Buffer was prepared using NaH2PO4 and Na2HPO4 which were purchased from Merck (www.merck.com).

Synthesis of CuWO4 In a typical procedure, 20 mL of 2.0 mM Cu(NO3)2.3H2O (dissolved in water) was mixed with 20 mL PEG and 20 mL of 2.0 mM Na2WO4.2H2O (dissolved in water). When the mixture was sonicated for 20 min, a green color suspension was obtained. This colloidal suspension was stirred at room temperature for 24 h, which was then kept in an autoclave at 200 °C ± 3 for 8 h, resulting in the formation of CuWO4. It was washed with absolute ethanol and distilled water, and dried at 400 °C for 2 h.

Synthesis of the CuWO4@PANI composite The CuWO4/PANI nanocomposite was synthesized at room temperature (35 °C) by chemical oxidative one

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step polymerization using (NH 4 ) 2 S 2 O 8 as oxidizing agent. The synthesized (2 mg) CuWO4 was dispersed in an ethanol solution (15 mL) in to which PVP (0.2 g), aniline (0.2 mL) and 0.2 M HCl were added. Then to the above solution, ammonium persulfate (20 mL, 0.05 g) was added whereupon the oxidative polymerization started under ultra-sonication. The solution was stirred for 6 h. The precipitate was filtered under vacuum and washed with water and ethanol. The product, CuWO4@PANI dried in a vacuum oven at 80 °C for 2 h.

Fig. 1 HR-TEM of CuWO4@PANI with different magnifications (a–d), SAED pattern of CuWO4@PANI (e) and EDX image of CuWO4@PANI (f)

Fabrication of modified glassy carbon electrodes Earlier, using aluminum oxide powder, the bare GCE (working electrode) was polished and ultrasonically cleaned with water and ethanol. Ag|AgCl as a reference electrode and Pt wire as an auxiliary electrode were used. All measurements were carried out at room temperature in an inert atmosphere in phosphate buffer (pH 6.0). The CVs were performed in the potential range between −0.3 to 0.5 V at the scan rate of 50 mVs−1. The CuWO4@PANI was dispersed ultrasonically in double distilled water. Then the solution of CuWO4@PANI

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c

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f

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(5 μL) was drop casted on the GCE surface, which was dried in an air oven. The CuWO4@PANI modified GCE obtained was washed carefully by deionized water and dried at room temperature. Simultaneously another two modified electrodes, CuWO4/GCE and PANI/GCE were also prepared following the same procedure. The synthesis of nanocomposite material and the mechanism of Qn sensing are illustrated schematically in Scheme 1.

Instrumentation CHI electrochemical workstation (Shanghai CH Instruments, Model CHI-660E) with conventional three electrode system was used for electrochemical measurements.The morphology of CuWO4@PANI was studied by TEM, FEI TECNAI T20 G2. TGA was carried out with TGA-50, HIMADZU. XRD analysis used JEOL JDX 8030 X-ray diffracto meter. FT-IR and UV-Vis spectra were obtained using JASCO FT-IR 460 Plus spectrophotometer and Jasco (V-560) model respectively.

Fig. 2 Cyclic voltammetry curves for the CuWO4@PANI modified GCE in the absence (a) and presence of 10 μM Qn with bare GCE (b), CuWO4/ GCE (c), PANI/GCE (d) and CuWO4@PANI/GCE (e) in phosphate buffer pH 6.0, at scan rate set at 50 mVs−1 in potential range of −0.3 to 0.5 V

Materials characterization The characterization of the materials using UV-Vis spectra, FT-IR spectra, XRD patterns and TGA analysis of CuWO4, PANI, CuWO4@PANI nanocomposite and the respective texts are given in the Electronic Supporting Materials (ESM). Fi gur e 1 sh ows t he HR- TEM imag es of CuWO4@PANI nanocomposite which exhibits a complete spherical morphology of CuWO4 and it is well bordered on PANI external. The TEM images of CuWO4@PANI with different magnifications are shown in Fig. 1a–d. The CuWO4 spheres are covered by a wall of PANI with an average diameter of 220 nm, as shown in Fig. 1c, d. The well crystalline nature of the nanocomposite, CuWO4@PANI is revealed by the selected area electron diffraction pattern as shown in (Fig. 1e). Figure 1f shows the energy dispersive X-ray analysis of the synthesized CuWO4@PANI nanocomposite which confirms the presence of Cu, W, O, C and N.

a

b

Electrochemical behavior of Qn Figure 2 shows the cyclic voltammograms of CuWO4@PANI/GCE (curve-a) at pH 6.0 in the absence of Qn. The observed major peak at the anodic and cathodic position indicates the redox reaction of Cu 2+ /Cu3+ at the CuWO4@PANI modified electrodes. Figure 2 (curve-b) shows the cyclic voltammogram in the presence of 10 μM Qn for bare GCE, CuWO 4 /GCE (curve-c), PANI/GCE (curve-d) and CuWO4@PANI/GCE (curve-e).The anodic peak current (Ipa) for the oxidation of Qn different electrodes are, 2.20 ± 0.10, 15.80 ± 0.02, 9.05 ± 0.03 μA, and 22.01 ± 0.003 μA respectively at GCE, CuWO4/GCE, PANI/GCE

Fig. 3 a DPV response of CuWO4@PANI/GCE in phosphate buffer (pH 6.0) at scan rate of 50 mV s−1 in the absence (curve a) and presence of a wide range of concentrations from 0.001 to 0.500 μM of Qn, at the working voltage of 0.15 V (vs. Ag/AgCl), (b) the calibration plot of the oxidation peak currents vs the concentrations of Qn

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Table 1 Comparison of the electrocatalytic oxidation of Qn using various electrode materials

Electrode materials

Method of detection

Linear range (μM)

LOD (μM)

Ref.

Fe3O4@ZnO/GCE MIP/MIL-101 (Cr)/MoS2/GCE g-C3N4/NiO/GCE

CV DPV DPV

0.79–610 0.1–700 0.010–230

0.16 0.02 0.002

[3] [4] [10]

Bare GCE MnWO4/GCE

DPV Chronoamperometric

0.1–15 16.7–74.4

0.0031 –

[20] [21]

Flower like Co3O4 /GCE CuWO4@PANI /GCE

SDV DPV

0. 5–330 0.010–0. 500

0.1 0.0012

[22] Present work

and CuWO4@PANI/GCE. In addition, the electroactive surface areas of the modified electrodes were calculated using the Randles− Sevcik equation [11] which are found to be 0.051, 0.092, 0.068, and 0.130 cm2 for bare GCE, CuWO4/GCE, PANI/GCE and CuWO4@PANI/GCE respectively. The current is almost 10 times enhanced due to the larger surface area provided by the CuWO4 embedded on PANI. The study on the effect of Qn concentration, scan rate, pH and interference can be found in ESM.

Calibration plot Figure 3a (curve-a) shows the differential pulse voltammetry (DPV) of CuWO4@PANI/GCE (pH 6.0) at scan rate of 50 mV s−1 in the absence of Qn. When Qn concentration is increased (0.001–0.500 μM), the peak current density observed at 0.142 V increases linearly as shown in Fig. 3a (curves b-g) & b, which suggests that the GCE modified with synthesized CuWO4@PANI can very well be used as a most promising electrode material for the detection of Qn. The

value of limit of detection (LOD) for this sensor is found to be 1.2 nM, with the correlation coefficient of 0.9989. LOD was calculated using the formula [19], LOD = 3.3S/b, where S is the standard deviation of the lowest concentration of Qn, and b is the slope of calibration plot obtained from the DPV. The sensitivity of the CuWO4@PANI/GCE is calculated to be 1.6025 μA μM−1 cm−2. The CuWO4@PANI nanocomposite has an outstanding sensing performance, good linear relationship, lower LOD and higher stability as illustrated in Table 1. [3, 4, 10, 20–22]. The improved electro-sensing performance of the electrode is able to be achieved by modifying it with the nanocomposite, CuWO4@PANI. Notwithstanding many binary metal oxides have been studied for electrochemical sensing, this is for the first time that CuWO4 has been used as a sensing material. The binary nanocomposite exhibits a strong synergistic effect which arises due to the interactions between CuWO4 and PANI resulting in the improvement of the electron transfer with enhanced electro chemical performance [11, 18].

Validation of the sensor Table 2 GCE Samples

Determination of Qn in various samples using CuWO4@PANI/ Added (nM)

Green Tea 0.5 Honey 0.5 Pear juice 0.5 Onion 0.5 Apple juice 0.5 Grape juice 0.5 Pregnant woman urine 0.5 blood 0.5 Adult man urine 0.5 blood 0.5

Found (nM)

Recovery (%)

*RSD (%)

0.5035 0.5065 0.5035 0.4930 0.4920 0.4960

100.7 101.3 100.7 98.6 98.4 99.2

0.86 0.94 0.99 1.61 2.73 1.36

0.5420 0.5820

108.4 116.4

0.98 0.54

0.5180 0.5410

103.6 108.20

0.87 0.91

*Related standard deviation (RSD) of three independent experiments

Real sample analysis was done on natural samples such as apple juice, grape juice, green tea, honey, onion and pear juice and blood and urine samples of pregnant woman and adult man. DPV was used for the real sample analysis and the standard addition method was used for the recovery calculation. Green tea, onion, honey were obtained from local market (Madurai, Tamilnadu).The best brand of tea (originated from Moonar, Tamilnadu) was purchased. Pear juice, apple juice and grape juice were purchased from local grocery stores (Madurai, Tamilnadu). Sample preparation: green tea (1.0 g), onion (2.0 g), honey (20 g) and pear, apple and grape juice (10 mL each), was taken in a flask and 40 mL of ethanol and 5 mL of HCl (6 mol.L−1) were added. After the mixture was stirred at 90 °C for 2 h in a water bath, it was cooled and filtered. Then the filtrate was diluted with ethanol. The standard addition experiments were carried out with three spiked levels of Qn (0.5 nM) and the results are shown in Table 2. The ability of the modified electrode for the detection of Qn

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Page 6 of 7 Scheme 2 Schematic representation of Qn sensing using CuWO4@PANI/GCE

was ascertained also in the blood and urine samples of a pregnant woman and an adult man (samples were diluted 100 times with buffer (pH 6.0)). The experimental conditions for the determination of Qn are similar to that stated above in the DPV study. The results tabulated in Table 2 suggest that the present sensor can be efficaciously applied for the detection of Qn in various real samples with reasonable recoveries. The probable mechanism of electron transfer for the detection of Qn at CuWO4@PANI nanocomposite is shown in Scheme 2.

samples. Thus this sensor can be very much used for the monitoring of Qn level in blood, urine and natural samples without much complicated pretreatment.

Compliance with ethical standards

References 1.

Conclusion In summary, the CuWO4@PANI nanocomposite has been synthesized by economical and scalable approach. The glassy carbon electrode coated with CuWO4@PANI nanocomposite was used for the detection of Qn. Not only does the CuWO4@PANI/GCE exhibit an extensive linear concentration range and LOD, but also exceptional reproducibility, selectivity and stability. Also, the experimental results reveal that the prepared sensor system exhibits sensitive signal responses to Qn over potential interferences from real natural

The author(s) declare

that they have no competing interests.

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