Ferricyanide/reduced graphene oxide as electron ...

Sensors and Actuators B 248 (2017) 708–717

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Ferricyanide/reduced graphene oxide as electron mediator for the electrochemical detection of methanol in canned citrus sinensis and citrus limetta Dinesh Kumar Subbiah a,b , Noel Nesakumar a,c , Arockia Jayalatha Kulandaisamy a,b , John Bosco Balaguru Rayappan a,b,∗ a

Nano Sensors Lab @ Centre for Nanotechnology and Advanced Biomaterials (CeNTAB), SASTRA University, Thanjavur 613401, Tamil Nadu, India School of Electrical & Electronics Engineering, SASTRA University, Thanjavur 613401, Tamil Nadu, India c School of Chemical & Biotechnology, SASTRA University, Thanjavur 613401, Tamil Nadu, India b

a r t i c l e

i n f o

Article history: Received 13 December 2016 Received in revised form 28 March 2017 Accepted 31 March 2017 Available online 8 April 2017 Keywords: Methanol Reduced graphene oxide Chitosan Ferricyanide ions Platinum electrode

a b s t r a c t The quality of exported canned citrus sinensis and citrus limetta degrades slowly owing to the excess liberation of methanol from the pectin of canned citrus sinensis and citrus limetta. To detect the methanol liberation, an electroactive inorganic-organic nanocomposite modified working electrode was fabricated by immobilizing reduced graphene oxide/ferricyanide (rGO/Fe(CN)6 3− ) on the surface of Pt electrode via chitosan membrane. The electrocatalytic oxidation of methanol by Fe(CN)6 3− was observed at the anodic potential of 243 mV (vs Ag/AgCl), which was shifted negatively to almost 36 mV when compared with that of direct electrochemical oxidation of Fe(CN)6 4− in the Pt/Chitosan/rGO/Ferricyanide electrode. The developed amperometric sensor could detect methanol concentration down to 12 nM with a linearity of 1–7 mM, sensitivity of 0.479 ␮A mM−1 , reproducibility of 1.2% RSD, repeatability of 1.1% RSD, response time of less than 10 s with the stability of 98% over a period of 20 days. © 2017 Elsevier B.V. All rights reserved.

1. INTRODUCTION Among various fruits, citrus fruits are the highest valued fruit crop in international trade [1,2]. South Asia and Spain are the world’s largest exporters of citrus limetta and citrus sinensis, accounting for 12 and 28.9% of all world citrus limetta and citrus sinensis productions, respectively. Prior to the exportation, citrus sinensis and citrus limetta are processed and sealed in an air tight container to increase its shelf life [3,4]. However, the quality of exported canned citrus sinensis and citrus limetta is being lowered owing to the excess liberation of methanol from the pectin of canned citrus sinensis and citrus limetta [5–7]. Canning may increase methanol concentration up to 560 mg L−1 in fresh citrus limetta and citrus sinensis. The regular consumption of methanol contaminated citrus limetta and citrus sinensis causes low blood pressure, coma, vision blurring, dizziness, headache and nausea in humans [5–7]. Therefore, it is the need of the hour to develop a

∗ Corresponding author at: Centre for Nanotechnology and Advanced Biomaterials (CeNTAB) and School of Electrical & Electronics Engineering, SASTRA University, Thanjavur 613401, India. Tel.: +91 4362264101x255; fax: +91 4362264120. E-mail address: [email protected] (J.B.B. Rayappan). http://dx.doi.org/10.1016/j.snb.2017.03.168 0925-4005/© 2017 Elsevier B.V. All rights reserved.

hand-held sensor for the quantification of methanol contamination in the canned citrus limetta and citrus sinensis. The voltammetric determination of methanol is usually based on its direct electrochemical oxidation on methanol dehydrogenase modified electrode surfaces [8–11]. The drawback of the methanol dehydrogenase modified electrodes are poor stability and high cost. In order to overcome these drawbacks, variety of nanomaterials such as carbon nanotubes (CNTs), platinum (Pt), nickel, reduced graphene oxide (rGO), graphene, nickel oxide, silver oxide, zinc oxide, copper, iron oxide, silica, ceria, titania and tin oxide have been used as electrocatalysts for the determination of methanol [8–11]. However, these modified working electrodes require high working potentials, which lead to poor sensitivity, electrode fouling and low selectivity [8–11]. Incorporation of good electron mediators onto the surface of working electrode could be a solution toward these limitations. In recent years, different organic-inorganic nanocomposites have been employed as electron mediators with the aim of reducing the working potential for the oxidation of methanol and enhancing the electron transfer rate between the surface-confined electroactive methanol and working electrode [12–16]. Copper-polyaniline, platinumpoly([Bvim][Br]-co-acrylonitrile), platinum-graphene, platinum-

D.K. Subbiah et al. / Sensors and Actuators B 248 (2017) 708–717

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Fig. 1. Schematic representation of synthesis of rGO/Fe(CN)6 3− nanocomposites.

poly-oxymethylene-dimethylether, platinum-polyaniline, pentoxide-poly(3,4-ethylenedioxythiophene), vanadium platinum-poly(5-methoxyindole), tin dioxidepolyaniline are the reported organic-inorganic nanocomposites used for methanol determination [12–16]. As a new approach, ferricyanide (Fe(CN)6 3− ) is considered to be the most attractive owing to its good electrochemical characteristics [17–20]. Furthermore, to enhance the performance of the methanol sensor, a greater amount of the immobilized Fe(CN)6 3− with a nanomaterial capable of shuttling electron rapidly between surface confined electroactive methanol and working electrode is preferred. Reduced graphene oxide (rGO) has recently received lot of attention in electrochemical sensors owing to its excellent electrical conductivity, biocompatibility, electrocatalytic ability, large specific surface area, extraordinary electronic property, rapid charge mobility and abundant functional groups for further modification [21–25]. Moreover, rGO can conduct electron through sp2 graphenic regions via Klein tunnelling, which exhibits high conductivity [21–25]. Hence, in this work, an electroactive inorganic-organic nanocomposite modified working electrode was developed for ultrasensitive detection of methanol by immobilizing rGO/Fe(CN)6 3− on the surface of Pt electrode via chitosan membrane. Moreover, the feasibility of the developed electrode for methanol detection in canned citrus sinensis and citrus limetta is also explored.

2. MATERIALS AND METHODS 2.1. Chemicals Graphite was purchased from Alfa Aesar, USA. Sodium nitrate was obtained from Sigma-Aldrich, USA. Chemicals namely mannitol, galactose, xylose, maltose, starch, fructose, sucrose, ethanol, formic acid, formaldehyde, sulfuric acid, dimethylformamide, hydrazine hydrate, ascorbic acid, potassium permanganate, methanol, monobasic sodium phosphate monohydrate, dibasic sodium phosphate dehydrate, hydrogen peroxide, 0.5 w/v% chitosan in 1% acetic acid (degree of deacetylation of 82.5%, molecular weight:140,000 gmol−1 ), hydrochloric acid, potassium hexacyanoferrate, lactic acid, glucose and sucrose were procured from Merck India Ltd., India.

2.2. Apparatus and instruments Scanning electron microscope (TESCAN, Model VEGA3, TESCAN, USA) was employed to observe the morphologies of Pt/Chitosan/GO, Pt/Chitosan/rGO and Pt/Chitosan/rGO/Ferricyanide electrodes’ surface. Amperometric, cyclic voltammetric and electrochemical impedance spectrometric measurements were performed on CHI600 series electrochemical analyzer (CH Instruments, USA). A conventional three electrode system was employed with Ag/AgCl saturated with 0.4 M KCl as reference electrode, platinum wire as auxiliary electrode and Pt/Chitosan/rGO/Ferricyanide as the working electrode.

2.3. Synthesis of rGO/Fe(CN)6 3− Graphene oxide (GO) was synthesized by modified Hummer’s method (Scheme 1) [26–29]. In a typical procedure, 1 g of graphite powder and 0.8 g of sodium nitrate were added to 30 mL of sulfuric acid. The mixture was kept under gentle stirring in an ice bath for 4 h. Then, 4 g of potassium permanganate was added slowly into the solution. The reaction mixture was stirred for 1 h at room temperature. Later, the resulting solution was added to 100 mL of deionized water and heated at 310 K for 1 h. After this, 30 w/v% of hydrogen peroxide (10 mL) was added to terminate the reaction. Immediately, the deep black color of solution changed to brown, which confirmed the formation of GO. The resultant solution was filtered and washed with 5 w/v% of HCl for several times. At last, the as-obtained graphene oxide was dried at room temperature for 24 h and stored for further use. After confirming the formation of GO, 1 g of GO was dispersed in 1 ␮L of hydrazine monohydrate and 100 ␮L of dimethylformamide and stirred at room temperature for 12 h. Subsequently, the mixture was kept under sonication for 2 h and then stirred at 353 K for 1 h. Immediately, the brown color of GO changed to black color, which confirmed the formation of rGO (Fig. 1). To obtain rGO/Fe(CN)6 3− composites, rGO (10 mg mL−1 ) was dispersed in 5 mL of K3 Fe(CN)6 solution and stirred at room temperature for 10 h. After centrifugation, greenish black colored rGO/Fe(CN)6 3− composites were obtained. The rGO/Fe(CN)6 3− composites were filtered and further washed three times with

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Table 1 Estimation of electrochemical parameters of different modified Pt electrodes. Electrochemical process

Anode

Cathode

Parameters

Pt

Pt/Chitosan

Pt/Chitosan/rGO

Pt/Chitosan/rGO/Ferricyanide

Ep (mV) Ret () Ipa (␮A) Ks (s−1 ) Q (␮C) (×10−9 M cm−2 ) Ipc (␮A) Ks (s−1 ) Q (␮C) (×10−9 M cm−2 )

107 1861 13.9 1.67 8.30 2.74 14.03 1.68 8.30 2.74

79 2479 6.98 0.44 15.74 5.19 7.75 0.44 17.53 5.78

133 2254 17.02 2.68 6.34 2.09 16.49 2.76 5.95 1.96

156 1805 18.86 3.65 5.16 1.70 17.69 3.62 4.88 1.61

deionized water. Finally, the as-prepared greenish black colored rGO/Fe(CN)6 3− composite was dried at room temperature (Fig. 1). 2.4. Fabrication of Pt/Chitosan/rGO/Ferricyanide electrode Prior to the beginning of each cyclic voltammetry experiment, the surface of Pt working electrode was polished with 0.05 ␮m alumina powder. After that the Pt working electrode surface was washed with 1 M KOH and later with 10 w/v% of HNO3 and distilled water subsequently. The cleaning procedure was performed to remove the oxide layer and other contaminants on the electrode surface. In order to fabricate Pt/Chitosan/rGO/Ferricyanide electrode (Fig. 2), 1 mg of rGO/Fe(CN)6 3− and 10 ␮L of chitosan were dispersed in PBS (0.1 M, pH 7.0). The mixture was sonicated for 2 h at room temperature. Then, 3 ␮L of the above suspension was drop casted onto the surface of the Pt working electrode. The Pt/Chitosan/rGO/Ferricyanide electrode was dried at room temperature for 4 h. On the other hand, various kinds of modified Pt modified electrodes such as Pt/Chitosan and Pt/Chitosan/rGO were also fabricated with a similar procedure. 2.5. Electrochemical characterization of methanol sensor Cyclic voltammetric experiments were performed in 0.1 M phosphate buffered saline at a scan rate of 0.01 Vs−1 . The amperometric experiments were carried out in a 20 mL electrochemical cell at an applied potential of 243 mV (vs. Ag/AgCl) under magnetic stirring at about 500 rpm/min. Electrochemical impedance spectroscopy (EIS) of the Pt modified electrodes was performed in ac frequency range varying from 0.1 Hz to 100 kHz at the standard reduction potential (Eo = 0.191 V vs. Ag/AgCl) of Fe(CN)6 3− : Fe(CN)6 4− redox couple in 0.1 M KCl solution. 3. RESULTS AND DISCUSSION 3.1. Surface morphologies of GO, rGO and rGO/Ferricyanide modified Pt electrodes The morphologies of Pt/Chitosan/GO, Pt/Chitosan/rGO and Pt/Chitosan/rGO/Ferricyanide electrodes were characterized using SEM (Fig. 3(a–c)). The morphologies of Pt/Chitosan/GO and Pt/Chitosan/rGO were in the form of irregular hexagonal prism, whereas the Pt/Chitosan/rGO/Ferricyanide showed rod-like morphology. 3.2. Electrochemical characterization of GO and rGO modified Pt electrodes To better understand the formation of GO, cyclic voltammetry experiments of bare Pt and Pt/rGO were performed in the potential range between −0.1 and −1.8 V at a scan rate of 0.01 Vs−1

(Fig. 4(a)). No redox peak was observed on bare Pt electrode, while the reduction peak appeared on Pt/GO due to the reduction of oxygen moieties (such as carboxyl, epoxide and hydroxyl) at the GO basal plane. Further, cyclic voltammetry experiment was also carried out using Pt/rGO modified electrode to confirm the formation of rGO. As shown in Fig. 4(a), the reduction peak disappeared completely due to the complete reduction of surface-oxygenated species at the GO basal plane. These results clearly revealed the impact of hydrazine monohydrate in the formation of rGO. 3.3. Electrochemical characterization of Pt/Chitosan/rGO/Ferricyanide electrodes Cyclic voltammetry and electrochemical impedance spectroscopy studies were performed to characterize the interface properties of the Pt modified electrodes. Fig. 4(b) shows the cyclic voltammograms of bare Pt, Pt/Chitosan, Pt/Chitosan/rGO and Pt/Chitosan/rGO/Ferricyanide in a solution of 0.1 M KCl containing 0.5 mM Fe(CN)6 . In the presence of 0.5 mM Fe(CN)6 , the capacitive current of chitosan modified Pt electrode was higher than that of bare Pt electrode, indicating the low electrical conductivity of chitosan membrane. Owing to its low electrical conductivity, chitosan membrane restricted the electron transfer probe ([Fe(CN)6 ]3−/4− ) toward the surface of Pt electrode. As a result, the redox peak current of chitosan modified Pt electrode reduced to one-half of the redox peak current value observed in bare Pt electrode. However, the immobilization of chitosan film on the surface of Pt electrode decreased the value of overpotential. Due to its positive charges, high degree of deacetylation (85%) and porosity, chitosan interacted with [Fe(CN)6 ]3−/4− from the surface of Pt electrode and enhanced the adsorption of electroactive [Fe(CN)6 ]3−/4− at Pt/Chitosan electrode. To further validate the proposed mechanism, amount of charge consumed (Q) and surface coverage () of electroactive [Fe(CN)6 ]3−/4− at bare Pt and Pt/Chitosan electrodes were estimated by integrating area under the redox peaks and employing Eq. (1), respectively. =

Ip (irrev.) 2.718RT n˛na F 2 A

(1)

where, A is the area of Pt working electrode, T is the room temperature, na is the number of electrons involved in the charge transfer step, F is the Faraday’s constant, Ip (irrev.) is the irreversible peak current, ␣ is the electron transfer coefficient, n is the number of electrons in the redox reaction and ␯ is the scan rate. The amount of charge consumed and surface coverage of electroactive [Fe(CN)6 ]3−/4− at Pt/Chitosan electrode were estimated as 15.74–17.53 ␮C and 5.19–5.78 × 10−9 M cm−2 , respectively (Table 1). The amount of charge consumed and surface coverage values of Pt/Chitosan electrode were much higher than that of other modified electrodes, indicating the enhanced adsorption of electroactive [Fe(CN)6 ]3−/4− at Pt/Chitosan electrode. Compared to the bare Pt and Pt/Chitosan electrodes, the Pt/Chitosan/rGO electrode exhibited larger redox peak current in the electrochemical pro-


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Fig. 2. Schematic illustration of sensing mechanism of electrocatalytic oxidation of methanol.

Fig. 3. SEM images of (a) Pt/Chitosan/GO, (b) Pt/Chitosan/rGO and (c) Pt/Chitosan/rGO/Ferricyanide.

cess, confirmed the role of rGO in enhancing the electron transfer between the electrochemical probe ([Fe(CN)6 ]3−/4− ) and Pt electrode (Table 1). The improved conductivity of rGO was due to the restoration of a graphitic network of Sp2 bonds. On the other hand, when ferricyanide was modified onto Pt/Chitosan/rGO electrode surface, the redox current dramatically increased to a greater extent. The increase in redox peak current was due to the high electrical conductivity of immobilized ferricyanide. In order to estimate the rate of electron transfer between the electrochemical probe ([Fe(CN)6 ]3−/4− ) and modified Pt electrodes, electron transfer rate constant (Ks ) was calculated using Eq. (2). Ks =

Ip Q

(2)

When compared with other modified Pt electrodes, Pt/Chitosan/rGO/Ferricyanide electrode showed an enhanced electron transfer rate (in cathode: Ks = 3.62 s−1 ; in anode: Ks = 3.65 s−1 ) in the electrochemical process (Table 1). These results also indicated that the immobilized ferricyanide improved the electron transfer ability of rGO modified Pt electrode. Fig. 4(c) represents the Nyquist plots of different modified Pt electrodes. The electrochemical impedance spectroscopy (EIS) data of the Pt modified electrodes were obtained in the frequency range of 0.1–100 kHz at the standard reduction potential (Eo = 0.191 V vs. Ag/AgCl) of Fe(CN)6 3− :Fe(CN)6 4− redox couple in 0.1 M KCl solution. The electron transfer resistance (Ret ) values of different modified Pt electrodes were obtained from the Warburg impedance equivalent circuit in which Cdl represents the double layer capacitance, Rs represents the electrolyte resistance and W is the Warburg impedance, which represents the diffusion process [30]. The linear part at low frequencies in EIS represents the diffusion process, whereas the semicircle at higher frequencies in

EIS indexes the electron transfer limited process. A small welldefined semicircle at high frequencies for Pt electrode indicated the lower electron transfer resistance (Table 1). Coating chitosan membrane on bare Pt electrode surface resulted in the drastic increase of impedance, depicting that the non-conductive chitosan membrane film greatly restricted the electron transfer from the electrochemical probe ([Fe(CN)6 ]3−/4− ) to the Pt electrode surface. However, compared to Pt/Chitosan electrode, the participation of rGO resulted in the significant decrease of electron transfer resistance for Pt/Chitosan/rGO electrode (Table 1). Owing to the good conductivity and enhanced electroactive area of rGO, rGO modified Pt/Chitosan electrode facilitated the electron transfer between [Fe(CN)6 ]3−/4− and Pt electrode. After immobilizing ferricyanide on the surface of Pt/Chitosan/rGO electrode, the electron transfer resistance decreased distinctively, manifesting that immobilized ferricyanide had accelerated the electron transfer between the electrochemical probe ([Fe(CN)6 ]3−/4− ) and Pt/Chitosan/rGO electrode. 3.4. Electrocatalysis of methanol on Pt/Chitosan/rGO/Ferricyanide electrode Fig. 4(d) shows the cyclic voltammograms of bare Pt, Pt/Chitosan, Pt/Chitosan/rGO and Pt/Chitosan/rGO/Ferricyanide in the absence and presence of 1 mM methanol in 0.1 M PBS (pH 7.0) at a scan rate of 0.1 Vs−1 . There were no redox peaks for bare Pt, Pt/Chitosan and Pt/Chitosan/rGO electrodes in the absence of methanol. However, when the Pt/Chitosan/rGO/Ferricyanide electrode was measured in oxygen dissolved PBS (0.1 M, pH 7.0), a pair of redox peaks was observed at 102 and 279 mV due to the reduction and oxidation of the bound Fe(CN)6 3− and Fe(CN)6 4− ions, respectively. With the addition of 1 mM methanol into the in oxygen dissolved PBS, the oxidation peak current decreased noticeably

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Fig. 4. (a) Cyclic voltammograms of Pt, Pt/GO and Pt/rGO in 0.1 M PBS (pH 7.0) at a scan rate of 0.01 Vs−1 , (b) cyclic voltammograms of bare Pt, Pt/Chitosan, Pt/Chitosan/rGO and Pt/Chitosan/rGO/Ferricyanide in a solution of 0.1 M KCl containing 0.5 mM Fe(CN)6 , (c) EIS for different modified Pt electrodes in a solution of 0.1 M KCl containing 0.5 mM Fe(CN)6 at an applied formal potential of 0.191 V (vs. Ag/AgCl), (d) cyclic voltammograms of bare Pt, Pt/Chitosan, Pt/Chitosan/rGO and Pt/Chitosan/rGO/Ferricyanide in the absence and presence of 1 mM methanol in 0.1 M PBS (pH 7.0) at a scan rate of 0.1 Vs−1 , (e) cyclic voltammograms of Pt/Chitosan/rGO/Ferricyanide electrode in 0.1 M PBS (pH 7.0) containing 1 mM methanol at different scan rates (0.01–0.09 Vs−1 ) and (f) calibration plot of anodic peak current vs. scan rate.

and the reduction peak current completely disappeared, showing a typical electrocatalytic reaction between methanol and Fe(CN)6 3− had occurred [31]. Owing to the presence of dissolved oxygen in PBS (0.1 M, pH 7.4), the electron produced due to the oxidation of CH3 OH to CH2 O was consumed by the dissolved oxygen in PBS at the surface of Pt/Chitosan/rGO/Ferricyanide electrode generating OH− (Eq. 3). 1/2O2 + H2 O + 2e− → 2OH−

(3) (E◦ )

of Ag/AgCl is Generally, the standard reduction potential 222.3 mV. And, the E◦ of 1/2O2 : OH− is 400 mV (vs. SHE). If the electrochemical reaction is performed with Ag/AgCl as reference electrode, then E◦ will shift to 178 mV. Since the formal potential of 1/2O2 : OH− redox couple is near to the oxidation potential of CH3 OH:CH2 O redox couple, dissolved oxygen consumed two elec-

trons, which was produced from the oxidation of CH3 OH to CH2 O. Owing to the presence of dissolved oxygen in 0.1 M PBS, there was a consumption of two electrons by dissolved oxygen. Thus, the two electrons produced from the oxidation of CH3 OH to CH2 O were not completely shuttled directly to Pt electrode via rGO nanointerface, which resulted in reduced anodic current response [32]. The electrocatalytic oxidation of methanol by Fe(CN)6 3− was noticed at the anodic potential of 243 mV, which was shifted negatively to almost 36 mV when compared with that of direct electrochemical oxidation of Fe(CN)6 4− on the Pt/Chitosan/rGO/Ferricyanide electrode. This provided a suitable platform for the estimation of methanol with the low working potential. The mechanism for electrocatalytic oxidation of methanol by Fe(CN)6 3− is given as follows (Fig. 2): CH3 OH + 2Fe(CN)6 3− → CH2 O + 2Fe(CN)6 4− + 2e− + 2H+

(4)


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Fig. 5. (a) Cyclic voltammetric current response of Pt/Chitosan/rGO/Ferricyanide electrode on successively increasing methanol concentrations at a scan rate of 0.01 Vs−1 , (b) linear dependence of the voltammetric current response vs. methanol concentration, (c) complex plane plots on Pt/Chitosan/rGO/Ferricyanide electrode for different concentrations of methanol in PBS (0.1 M, pH 7.0) at an applied potential of 243 mV (vs. Ag/AgCl), (d) linear dependence of Ret vs. methanol concentration (e) amperometric current response of Pt/Chitosan/rGO/Ferricyanide electrode to successive addition of methanol in PBS (0.1 M, pH 7.0) at 243 mV (vs. Ag/AgCl) and (f)) linear dependence of the amperometric current response vs. methanol concentration.

Fe(CN)6 4− → Fe(CN)6 3− + e−

(5)

Methanol was first electrochemically oxidized to formaldehyde by the Fe(CN)6 3− ion trapped in the modified Pt electrode (Eq. (4)). Subsequently, the resulting Fe(CN)6 4− ion electrochemically reoxidized to Fe(CN)6 3− for further participation in the electrocatalytic reaction with methanol. The Ks value obtained for the proposed Pt/Chitosan/rGO/Ferricyanide electrode was 4.4 s−1 , suggesting that rGO/Ferricyanide provided an excellent medium for methanol adsorption and for electrical communication between the adsorbed electroactive methanol and Pt electrode. As a result, the direct electron transfer of adsorbed electroactive methanol was facilitated. The concentration of adsorbed electroactive methanol () on the surface of Pt/Chitosan/rGO/Ferricyanide electrode was calculated using Eq. (1). The calculated value for was about 6.74 × 10−10 mol cm−2 , indicating that the enhanced surface cov-

erage of electroactive methanol was due to large electroactive area of rGO/Ferricyanide composites.

3.5. Effect of scan rate on Pt/Chitosan/rGO/Ferricyanide electrode In electrochemical methanol sensor, the oxidation process may be diffusion or surface controlled. If electroactive methanol gets adsorbed on the surface of Pt/Chitosan/rGO/Ferricyanide electrode, then the oxidation of methanol to formaldehyde by Fe(CN)6 3− ion will occur at the surface of Pt/Chitosan/rGO/Ferricyanide electrode directly. This redox process will be surface confined. As a result, the oxidation peak current will increase with increasing scan rate. However, if electroactive methanol does not get adsorbed on the surface of Pt/Chitosan/rGO/Ferricyanide electrode, then the oxidation of methanol to formaldehyde will be depen-

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Fig. 6. Amperometric current responses for successive addition of 20 ␮L concentrations of (a) canned citrus limetta and (b) citrus sinensis extracts on (i) day 1, (ii) day 2, (iii) day 3, (iv) day 4 and (iv) day 5 in PBS (0.1 M, pH 7.0).

dent on how fast it diffuses from PBS (0.1 M, pH 7.0) toward Pt/Chitosan/rGO/Ferricyanide electrode. In such a case, the anodic oxidation process will be under diffusion controlled. As a consequence, the oxidation peak current will be proportional to square root of the scan rate. Fig. 4(e) shows the cyclic voltammetric responses of the Pt/Chitosan/rGO/Ferricyanide electrode in 0.1 M PBS (pH 7.0) containing 1 mM methanol at different scan rates (0.01–0.09 Vs−1 ). With increasing scan rate (0.01–0.09 Vs−1 ), the oxidation peak current was linearly (Ipa (␮A) = 51.715 [␯] (Vs−1 ) + 0.219, R2 = 0.99) proportional to the scan rate with a correlation coefficient of 0.99 (Fig. 4(f)). Furthermore, the increase in anodic peak-to-peak separation depicted the limitation resulting from electron transfer kinetics rather than diffusion process.

3.6. Cyclic voltammetric, impedimetric and amperometric determination of methanol Fig. 4(a) shows the cyclic voltammetric current response of Pt/Chitosan/rGO/Ferricyanide electrode on successively increasing methanol concentrations at a scan rate of 0.01 Vs−1 . As shown in Fig. 5(a), the intensity of anodic oxidation current response increased with the increase of methanol concentration from 1 to 7 mM. The corresponding calibration curve for the developed electrode toward methanol is shown in Fig. 5(b). The response of the Pt/Chitosan/rGO/Ferricyanide electrode was linear (Ipa (␮A) = 0.474 [methanol] (mM) + 0.128) toward methanol concentration in the range between 1 and 7 mM with a regression coefficient of 0.99 and a sensitivity of 0.474 ␮A mM−1 . Fig. 5(c) shows the complex plane plots obtained on Pt/Chitosan/rGO/Ferricyanide electrode for different concentrations of methanol in PBS (0.1 M, pH 7.0) at an applied potential of 243 mV vs. Ag/AgCl. The EIS data were approximated using well-known Randles model, comprising of a double layer capacitance shunted by Warburg impedance, in series with solution resistance (Fig. 5(d)). As the concentration of methanol increased from 1 to 7 mM, the electron transfer resistance decreased to a greater extent. The respective calibration plot of Ret vs. methanol concentration exhibited a linear (Ret (k) = −0.212 [methanol] (mM) + 2.765) range from 1 to 7 mM with a regression coefficient of 0.99 and sensitivity of −0.212 k mM−1 (Fig. 5(d)). Since the electrocatalytic oxidation of methanol by Fe(CN)6 3− was observed at the anodic potential of 243 mV, an operating potential of 243 mV was applied for the amperometric determination of methanol. The amperometric current response of the Chitosan/rGO/Ferricyanide modified Pt electrode to successive addition of methanol in PBS (0.1 M, pH 7.0) at 243 mV is shown in Fig. 5(e). When the methanol was added to the stirred

PBS (0.1 M, pH 7.0), the Pt/Chitosan/rGO/Ferricyanide electrode responded quickly and 95% of the steady-state current response could be obtained within 10 s. The current increased with the increase of methanol concentration from 1 to 7 mM. Fig. 5(f) shows the calibration curve of the amperometric response of the Pt/Chitosan/rGO/Ferricyanide electrode to the concentration of methanol. The linear range of the developed electrode for the estimation of methanol was found to be in the range of 1–7 mM with a sensitivity of 0.479 ␮A mM−1 and regression coefficient of 0.99. A detection limit of 12 nM was obtained based on 3Sb /S (where Sb is the standard deviation in the blank PBS and S is the slope of the calibration curve). 3.7. Stability, repeatability and reproducibility studies of methanol sensor Stability, reproducibility and repeatability of the developed Pt/Chitosan/rGO/Ferricyanide electrode in the dry state at room temperature were studied. The reproducibility of Pt/Chitosan/rGO/Ferricyanide electrode was assessed by measuring the amperometric current of eight similar independently fabricated electrodes. The amperometric current response of each Pt/Chitosan/rGO/Ferricyanide electrode was measured in PBS (0.1 M, pH 7.0) containing 1 mM methanol. An almost similar amperometric current response was observed for all eight independently fabricated electrodes. A low relative standard deviation (RSD = 1.2%) of modified Pt electrodes amperometric current response confirmed excellent reproducibility of the Pt/Chitosan/rGO/Ferricyanide electrode. The storage stability and repeatability of the methanol sensor was assessed by measuring the amperometric current response to 1 mM methanol solution for every 2 days over the period of 20 days. The electrocatalytic response of Pt/Chitosan/rGO/Ferricyanide electrode could retain 98% of its original response after 20 days with a low relative standard deviation of 1.1%. Thus, the Pt/Chitosan/rGO/Ferricyanide electrode exhibited good repeatability, reproducibility and stability for methanol detection. 3.8. Interference study In this work, interferents such as mannitol, galactose, xylose, maltose, starch, fructose, sucrose, ethanol, formic acid, formaldehyde, ascorbic acid, lactic acid, sucrose and glucose were chosen that often coexist with methanol in citrus sinensis and citrus limetta and could impact the accurate determination of methanol. The influence of interferents was examined via amperometry it curve at the Pt/Chitosan/rGO/Ferricyanide with 1 mM methanol


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Table 2 Quantification of methanol in the canned citrus sinensis and citrus limetta extracts. Day

1 2 3 4 5

Canned citrus limetta

Canned citrus sinensis

Spiked amount

Measured Current

Methanol found

Spiked amount

Measured Current

Methanol found

(␮L) 20 20 20 20 20

(␮A) 0.914 0.974 1.055 1.149 1.268

(mM) 1.162 1.288 1.457 1.653 1.901

(␮L) 20 20 20 20 20

(␮A) 0.979 1.052 1.138 1.247 1.497

(mM) 1.298 1.450 1.630 1.858 2.379

Table 3 Comparision of previously reported electrochemical methanol sensors with the proposed methanol sensor. Working electrode

Detection technique

Linear range (mM)

LOD (␮M)

Reference

CEF-Ni(II)/Chitosan/GC Pt/CNTs Methanol dehydrogenase/GC Pd–Ni/SiNWs Ni(II)-BS complex/CPE Ni(II)-DHS/GC Ni-Pd/Si-MCP Pt/GC Ferricyanide/rGO/Chitosan/Pt

Amperometry Cyclic voltammetry Amperometry Amperometry Differential pulse voltammetry Amperometry Amperometry Chronoamperometry Amperometry

0.02–12 25–100 0–0.2 0–75 0.5 × 10−3 –0.1 0.05 × 10−3 –0.3 × 10−3 2.5–27.5 0.25–10000 1–7

5.24 >60 0.5 25 0.19 0.026 12 100 0.012

[34] [32] [33] [37] [35] [38] [38] [36] Present work

in the absence and presence of 0.1 mM of mannitol, galactose, xylose, maltose, starch, fructose, sucrose, ethanol, formic acid, formaldehyde, ascorbic acid, lactic acid, sucrose and glucose. The amperometric current responses to 1 mM methanol before and after spiking of 0.1 mM of tested interferents were mostly constant. Thus, these tested interferents did not affect the amperometric response of Pt/Chitosan/rGO/Ferricyanide toward methanol. 3.9. Application Quantification of methanol present in the canned citrus sinensis and citrus limetta extracts was investigated by intermittently measuring the current response to 20 ␮L of canned citrus sinensis and citrus limetta extracts every day over a period of five days. Fig. 6(a and b) shows the amperometric current responses for successive addition of 20 ␮L concentrations of canned citrus sinensis and citrus limetta extracts on (i) day 1, (ii) day 2, (iii) day 3, (iv) day 4 and (iv) day 5 in PBS (0.1 M, pH 7.0) under optimized experimental conditions. There was just background current for Pt/Chitosan/rGO/Ferricyanide in the absence of 20 ␮L of canned citrus sinensis and citrus limetta extracts. With the addition of 20 ␮L of canned citrus sinensis and citrus limetta extracts in PBS (0.1 M, pH 7.0), the amperometric current response showed a welldefined signal in the form of current steps and attained 95% of its steady state value within 10 s, reflecting the rapid response of Pt/Chitosan/rGO/Ferricyanide to methanol. Upon successive addition of 20 ␮L of canned citrus sinensis and citrus limetta extracts individually to PBS (0.1 M, pH 7.0) from day 1 to day 5, the amperometric current response increased to a greater extent. The calibrated linear regression equation from the amperometric current response is given as follows (Eq. (6)), I (A) = 0.479 [Methanol] mM + 0.357 A

By knowing the value of amperometric current, quantification of methanol in the canned citrus sinensis and citrus limetta extracts can be determined. The unknown concentration of methanol in the canned citrus sinensis and citrus limetta extracts was determined using Eq. (6) and given in Table 2. The concentrations of methanol present in canned citrus sinensis and citrus limetta extracts measured from day 1 to day 5 were in the range of 1.298–2.379 and 1.162–1.901 mM, respectively, suggesting that the developed Pt/Chitosan/rGO/Ferricyanide electrode can be used for the determination of methanol in citrus fruits. In addition, the performance of the fabricated Pt/Chitosan/rGO/Ferricyanide electrode was compared with other electrochemical methanol sensors. As depicted in Table 3, it was apparent that the Pt/Chitosan/rGO/Ferricyanide electrode possessed lower detection limit than other reported electrochemical methanol sensors [33–39]. 4. CONCLUSIONS An electroactive inorganic-organic nanocomposite modified working electrode was fabricated by immobilizing reduced graphene oxide/ferricyanide (rGO/Fe(CN)6 3− ) on the surface of Pt electrode via chitosan membrane. The prepared rGO/Fe(CN)6 3− material acted as a good electron mediator for the electrocatalytic oxidation toward methanol in canned citrus sinensis and citrus limetta. The fabricated Pt/Chitosan/rGO/Ferricyanide electrode exhibited good performance with enhanced selectivity and low detection limit. In addition, the proposed fabrication strategy exhibited a large potential toward the electrocatalytic detection of biomolecules in canned food stuffs aside from methanol. Since the electrochemically synthesized rGO has high electrical conductivity, it can be also fabricated on the surfaces of cotton to produce the electrically conductive fabrics.

(6) ACKNOWLEDGMENTS

Keeping methanol concentration on the left hand side of the Eq. (7), we get, [Methanol] (mM) =

I (A) − 0.357 A 0.479 A mM −1

(7)

The authors are grateful to the Department of Science & Technology, New Delhi for their financial support (SR/NM/NT1039/2015, DST/TM/WTI/2K14/197(a)(G)), (SR/FST/ETI-284/2011 (C)), (SR/FST/LSI-453/2010), and (SR/NM/PG-16/2007). We also

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acknowledge SASTRA University, Thanjavur for extending infrastructure support to carry out the study. References [1] T. Defraeye, P. Verboven, U.L. Opara, B. Nicolai, P. Cronjé, Feasibility of ambient loading of citrus fruit into refrigerated containers for cooling during marine transport, Biosyst. Eng. 134 (2015) 20–30, doi:http://dx.doi.org/10.1016/j.biosystemseng.2015.03.012. [2] A. Gordon, Chapter 1 - Exporting traditional fruits and vegetables to the United States: trade, food science, and sanitary and phytosanitary/technical barriers to trade considerations, in: A. Gordon (Ed.), Food Saf. Qual. Syst. Dev. Ctries., Academic Press, San Diego, 2015, pp. 1–15, doi:http://dx.doi.org/10.1016/B978-0-12-801227-7.00001-9. [3] C.H. Zhu, E.R. Gertz, Y. Cai, B.J. Burri, Consumption of canned citrus fruit meals increases human plasma ␤-cryptoxanthin concentration, whereas lycopene and ␤-carotene concentrations did not change in healthy adults, Nutr. Res. 36 (2016) 679–688, http://dx.doi.org/10.1016/j.nutres.2016.03.005. [4] Y. Shan, Canned citrus processing: techniques, equipment, and food safety, 2015. [5] H. Zegota, High-performance liquid chromatography of methanol released from pectins after its oxidation to formaldehyde and condensation with 2,4-dinitrophenylhydrazine, J. Chromatogr. A. 863 (1999) 227–233, doi:http://dx.doi.org/10.1016/S0021-9673(99)00985-1. [6] W. PILNIK, A.G.J. VORAGEN, {CHAPTER} 14 - Pectic enzymes in fruit and vegetable juice manufacture, in: T. Nagodawithana, G. Reed (Eds.), Enzym. Food Process., Third Ed., Third Edit, Academic Press, London, 1993, pp. 363–399, doi:http://dx.doi.org/10.1016/B978-0-08-057145-4.50021-9. [7] C.-Y. Hou, Y.-S. Lin, Y.T. Wang, C.-M. Jiang, M.-C. Wu, Effect of storage conditions on methanol content of fruit and vegetable juices, J. Food Compos. Anal. 21 (2008) 410–415, doi:http://dx.doi.org/10.1016/j.jfca.2008.04.004. [8] M.M. Rahman, M.A. Hussein, K.A. Alamry, F.M. Al Shehry, A.M. Asiri, Sensitive methanol sensor based on PMMA-G-CNTs nanocomposites deposited onto glassy carbon electrodes, Talanta. 150 (2016) 71–80, http://dx.doi.org/10. 1016/j.talanta.2015.12.012. [9] S.H. Patil, B. Anothumakkool, S.D. Sathaye, K.R. Patil, Architecturally designed Pt-MoS2 and Pt-graphene composites for electrocatalytic methanol oxidation, Phys. Chem. Chem. Phys. 17 (2015) 26101–26110, http:// dx.doi.org/10.1039/c5cp04141d. [10] Z. Mousavi, A. Benvidi, S. Jahanbani, M. Mazloum-Ardakani, R. Vafazadeh, H.R. Zare, Investigation of electrochemical oxidation of methanol at a carbon paste electrode modified with Ni(II)-BS complex and reduced graphene oxide nano sheets, Electroanalysis. (2016), http://dx.doi.org/10.1002/elan.201501183. [11] A. Afraz, A.A. Rafati, A. Hajian, M. Khoshnood, Electrodeposition of Pt nNanoparticles on new porous graphitic carbon nanostructures prepared from biomass for fuel cell and methanol sensing applications, Electrocatalysis. 6 (2015) 220–228, http://dx.doi.org/10.1007/s12678-014-0234-x. [12] M.U.A. Prathap, T. Pandiyan, R. Srivastava, Cu nanoparticles supported mesoporous polyaniline and its applications towards non-enzymatic sensing of glucose and electrocatalytic oxidation of methanol, J. Polym. Res. 20 (2013), http://dx.doi.org/10.1007/s10965-013-0083-y. [13] C. Pan, L. Qiu, Y. Peng, F. Yan, Facile synthesis of nitrogen-doped carbon-Pt nanoparticle hybrids via carbonization of poly([Bvim][Br]-co-acrylonitrile) for electrocatalytic oxidation of methanol, J. Mater. Chem. 22 (2012) 13578–13584, http://dx.doi.org/10.1039/c2jm31973j. [14] T. Maiyalagan, B. Viswanathan, Synthesis, characterization and electrocatalytic activity of Pt supported on poly (3,4-ethylenedioxythiophene)-V2O5 nanocomposites electrodes for methanol oxidation, Mater. Chem. Phys. 121 (2010) 165–171, http://dx.doi. org/10.1016/j.matchemphys.2010.01.003. [15] B. Habibi, M.H. Pournaghi-Azar, Methanol oxidation on the polymer coated and polymer-stabilized Pt nano-particles: a comparative study of permeability and catalyst particle distribution ability of the PANI and its derivatives, Int. J. Hydrogen Energy. 35 (2010) 9318–9328, http://dx.doi.org/ 10.1016/j.ijhydene.2010.01.088. [16] M. Babaei, N. Alizadeh, Methanol selective gas sensor based on nano-structured conducting polypyrrole prepared by electrochemically on interdigital electrodes for biodiesel analysis, Sens. Actuators B Chem. 183 (2013) 617–626, http://dx.doi.org/10.1016/j.snb.2013.04.045. [17] C. Qin, W. Wang, C. Chen, L. Bu, T. Wang, X. Su, et al., Amperometric sensing of nitrite based on electroactive ferricyanide–poly(diallyldimethylammonium)–alginate composite film, Sens. Actuators B Chem. 181 (2013) 375–381, doi:http://dx.doi.org/10.1016/j.snb.2013.01.052. [18] S. He, Q. Wang, Y. Yu, Q. Shi, L. Zhang, Z. Chen, One-step synthesis of potassium ferricyanide-doped polyaniline nanoparticles for label-free immunosensor, Biosens. Bioelectron. 68 (2015) 462–467, doi:http://dx.doi.org/10.1016/j.bios.2015.01.018. [19] P. Gros, H. Durliat, M. Comtat, Use of polypyrrole film containing Fe(CN)3 3as pseudo-reference electrode: application for amperometric biosensors, Electrochim. Acta. 46 (2000) 643–650.

[20] P. Gros, M. Comtat, A bioelectrochemical polypyrrole-containing Fe(CN)63interface for the design of a NAD-dependent reagentless biosensor, Biosens. Bioelectron. 20 (2004) 204–210, http://dx.doi.org/10.1016/j.bios.2004.02.023. [21] Ö.A. Yokus¸, F. Kardas¸, O. Akyildirim, T. Eren, N. Atar, M.L. Yola, Sensitive voltammetric sensor based on polyoxometalate/reduced graphene oxide nanomaterial: application to the simultaneous determination of l-tyrosine and l-tryptophan, Sens. Actuators B Chem. 233 (2016) 47–54, http://dx.doi. org/10.1016/j.snb.2016.04.050. [22] J. Wang, B. Yang, K. Zhang, D. Bin, Y. Shiraishi, P. Yang, et al., Highly sensitive electrochemical determination of sunset yellow based on the ultrafine Au-Pd and reduced graphene oxide nanocomposites, J. Colloid Interface Sci. 481 (2016) 229–235, http://dx.doi.org/10.1016/j.jcis.2016.07.061. [23] M. Rosy, R.N. Raj, Goyal, A facile method to anchor reduced graphene oxide polymer nanocomposite on the glassy carbon surface and its application in the voltammetric estimation of tryptophan in presence of 5-hydroxytryptamine, Sens. Actuators B Chem. 233 (2016) 445–453, http:// dx.doi.org/10.1016/j.snb.2016.04.097. [24] Y. Luo, F.-Y. Kong, C. Li, J.-J. Shi, W.-X. Lv, W. Wang, One-pot preparation of reduced graphene oxide-carbon nanotube decorated with Au nanoparticles based on protein for non-enzymatic electrochemical sensing of glucose, Sens. Actuators B Chem. 234 (2016) 625–632, http://dx.doi.org/10.1016/j.snb.2016. 05.046. [25] S. Jampasa, W. Siangproh, K. Duangmal, O. Chailapakul, Electrochemically reduced graphene oxide-modified screen-printed carbon electrodes for a simple and highly sensitive electrochemical detection of synthetic colorants in beverages, Talanta. 160 (2016) 113–124, http://dx.doi.org/10.1016/j. talanta.2016.07.011. [26] H. Saleem, A. Habib, Study of band gap reduction of TiO2 thin films with variation in GO contents and use of TiO2/Graphene composite in hybrid solar cell, J. Alloys Compd. 679 (2016) 177–183, http://dx.doi.org/10.1016/j.jallcom. 2016.03.240. [27] B. Paul, D.D. Purkayastha, S.S. Dhar, S. Das, S. Haldar, Facile one-pot strategy to prepare Ag/Fe2O3 decorated reduced graphene oxide nanocomposite and its catalytic application in chemoselective reduction of nitroarenes, J. Alloys Compd. 681 (2016) 316–323, http://dx.doi.org/10.1016/j.jallcom.2016.04.229. [28] Y. Liu, Y. Zhang, L. Duan, W. Zhang, M. Su, Z. Sun, et al., Polystyrene/graphene oxide nanocomposites synthesized via Pickering polymerization, Prog. Org. Coatings. 99 (2016) 23–31, http://dx.doi.org/10.1016/j.porgcoat.2016.04.034. [29] R. Atchudan, T.N.J.I. Edison, S. Perumal, D. Karthikeyan, Y.R. Lee, Facile synthesis of zinc oxide nanoparticles decorated graphene oxide composite via simple solvothermal route and their photocatalytic activity on methylene blue degradation, J. Photochem. Photobiol. B Biol. 162 (2016) 500–510, http:// dx.doi.org/10.1016/j.jphotobiol.2016.07.019. [30] B. Kowalewska, K. Jakubow, The impact of immobilization process on the electrochemical performance, bioactivity and conformation of glucose oxidase enzyme, Sens. Actuators B Chem. 238 (2017) 852–861, http://dx.doi. org/10.1016/j.snb.2016.07.138. [31] F. Li, C. Tang, S. Liu, G. Ma, Development of an electrochemical ascorbic acid sensor based on the incorporation of a ferricyanide mediator with a polyelectrolyte–calcium carbonate microsphere, Electrochim. Acta. 55 (2010) 838–843, doi:http://dx.doi.org/10.1016/j.electacta.2009.09.049. [32] N. Nesakumar, K. Thandavan, S. Sethuraman, U.M. Krishnan, J.B.B. Rayappan, An electrochemical biosensor with nanointerface for lactate detection based on lactate dehydrogenase immobilized on zinc oxide nanorods, J. Colloid Interface Sci. 414 (2014) 90–96, doi:http://dx.doi.org/10.1016/j.jcis.2013.09.052. [33] D.W. Kim, J.S. Lee, G.S. Lee, L. Overzet, M. Kozlov, E.a. Aliev, et al., Carbon nanotubes based methanol sensor for fuel cells application, J. Nanosci. Nanotechnol. 6 (2006) 3608–3613, http://dx.doi.org/10.1166/jnn.2006.066. [34] Q. Liu, J.R. Kirchhoff, Amperometric detection of methanol with a methanol dehydrogenase modified electrode sensor, J. Electroanal. Chem. 601 (2007) 125–131, http://dx.doi.org/10.1016/j.jelechem.2006.10.039. [35] Y. Liu, S. Luo, W. Wei, X. Liu, X. Zeng, Methanol sensor based on the combined electrocatalytic oxidative effect of chitosan-immobilized nickel(II) and the antibiotic cefixime on the oxidation of methanol in alkaline medium, Microchim. Acta. 164 (2009) 351–355, http://dx.doi.org/10.1007/s00604-0080064-8. [36] Z. Mousavi, A. Benvidi, S. Jahanbani, M. Mazloum-ardakani, Investigation of electrochemical oxidation of methanol at a carbon paste electrode modified with Ni (II) -BS complex and reduced graphene oxide nano sheets, 2016, pp. 1–9, http://dx.doi.org/10.1002/elan.201501183. [37] D.S. Park, M.S. Won, R.N. Goyal, Y.B. Shim, The electrochemical sensor for methanol detection using silicon epoxy coated platinum nanoparticles, Sens. Actuators B Chem. 174 (2012) 45–50, http://dx.doi.org/10.1016/j.snb.2012.08. 017. [38] B. Tao, J. Zhang, S. Hui, X. Chen, L. Wan, An electrochemical methanol sensor based on a Pd-Ni/SiNWs catalytic electrode, Electrochim. Acta. 55 (2010) 5019–5023, http://dx.doi.org/10.1016/j.electacta.2010.04.013. [39] P. Taylor, F. Miao, B. Tao, P.K. Chu, Nickel-palladium nanoparticles for nonenzymatic methanol detection, Anal. Lett. 45 (2012) 37–41, http://dx.doi. org/10.1080/00032719.2012.675495.


Biographies

Dinesh Kumar Subbiah received M.Tech. in Nanoelectronics from SASTRA University, Thanjavur in 2016 and B.E. Electrical and Electronics Engineering in 2014, from Anna University. He is currently working as Research Scholar in the Centre for Nanotechnology and Advanced Biomaterials (CeNTAB) and School of Electrical & Electronics Engineering, SASTRA University, Thanjavur, India. His current research interests are modification of nanostructured textiles for UV filter applications. His research areas include Textile Technology, Chemiresistive gas sensors and Electrochemical biosensors. Noel Nesakumar gained a B.E. in Bio-medical Instrumentation at Anna University in 2010 and a M. Tech. degree in Medical Nanotechnology from SASTRA University in 2012. He received his Ph.D degree in School of Electrical & Electronics Engineering, SASTRA University, Thanjavur, India, in 2016. His area of focus as a researcher is the development of electrochemical biosensors for early detection of harmful chemicals in agroproducts.

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Arockia Jayalatha Kulandaisamy received her M.Sc. and Ph.D. degrees in Physics during 2002 and 2010 from Madurai Kamaraj University, Madurai and Bharathidasan University, Tiruchirappalli, respectively. She is currently working as Assistant Professor in the School of Electrical & Electronics Engineering, SASTRA University, Thanjavur, India. Her research interests include theoretical characterization of nanoparticles, nanosystem modelling and nanosensors.

John Bosco Balaguru Rayappan received his M.Sc. and Ph.D. degrees in Physics from Bharathidasan University, Tiruchirapalli, India in 1996 and 2003, respectively. He is currently working as a Professor in School of Electrical & Electronics Engineering and Centre for Nanotechnology and Advanced Biomaterials (CeNTAB), SASTRA University. His current research interests include lattice dynamics, fabrication of thin film based chemical & biosensors and functional nanomaterials. He is also working in the field of embedded systems and steganography.