Hydrogen peroxide sensor: Uniformly decorated silver nanoparticles on polypyrrole for wide detection range

Applied Surface Science 357 (2015) 1565–1572

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Hydrogen peroxide sensor: Uniformly decorated silver nanoparticles on polypyrrole for wide detection range Pooria Moozarm Nia ∗ , Woi Pei Meng, Y. Alias ∗ Department of Chemistry, University of Malaya, Kuala Lumpur 50603, Malaysia

a r t i c l e

i n f o

Article history: Received 25 July 2015 Received in revised form 1 October 2015 Accepted 5 October 2015 Keywords: Electrodeposition Polypyrrole Silver nanoparticles Hydrogen peroxide Sensor

a b s t r a c t Electrochemically synthesized polypyrrole (PPy) decorated with silver nanoparticles (AgNPs) was prepared and used as a nonenzymatic sensor for hydrogen peroxide (H2 O2 ) detection. Polypyrrole was fabricated through electrodeposition, while silver nanoparticles were deposited on polypyrrole by the same technique. The field emission scanning electron microscopy (FESEM) images showed that the electrodeposited AgNPs were aligned along the PPy uniformly and the mean particle size of AgNPs is around 25 nm. The electrocatalytic activity of AgNPs-PPy-GCE toward H2 O2 was studied using chronoamperometry and cyclic voltammetry. The first linear section was in the range of 0.1–5 mM with a limit of detection of 0.115 ␮mol l−1 and the second linear section was raised to 120 mM with a correlation factor of 0.256 ␮mol l−1 (S/N of 3). Moreover, the sensor presented excellent stability, selectivity, repeatability and reproducibility. These excellent performances make AgNPs-PPy/GCE an ideal nonenzymatic H2 O2 sensor. © 2015 Elsevier B.V. All rights reserved.

1. Introduction In the recent decades, the hydrogen peroxide (H2 O2 ) detection has gained huge interest due to its important role in the biochemical, chemical, pharmaceutical and various other fields [1]. Many different methods have been developed for detecting H2 O2 , such as spectrophotometry [2], titrimetry [3], chemiluminescence [4], chromatography [5], spectrofluorometry [6], and electrochemistry [7–10]. The electrochemical nonenzymatic sensors have been extremely used in determination of H2 O2 due to their high sensitivity and their good selectivity. The composites containing metal nanoparticles and conducting polymers (CPs) are very interesting materials due to their easy preparation, high conductivity and good environmental stability as well as their catalytic properties [11–20]. The electrodeposition of conducting polymers and metallic particles can be carried out independently in the same solution containing both components [11,21] or in two different solutions (one containing the monomer and the other the metal salt) [14,22,23]. Through electrochemical techniques, by controlling electrodeposition time, current and potential, the composition and the structure of composites can be modified. The amount, dispersion and method of incorporating

∗ Corresponding authors. E-mail addresses: [email protected] (P.M. Nia), [email protected] (W.P. Meng), [email protected] (Y. Alias). http://dx.doi.org/10.1016/j.apsusc.2015.10.026 0169-4332/© 2015 Elsevier B.V. All rights reserved.

particles of metal into the conducting polymer film have a considerable effect on the catalytic properties of these materials [24,25]. The combination of conducting polymers with metal particles gives a promising way to strengthen the CPs as well as introducing electrical properties based on the electrical synergy between the two components. By reducing the size of the materials to nanoscale, the conducting polymer–metal composite properties further increased [26–29]. In nanocomposites, the electrocatalytic activities increased with reducing the material sizes [11,30–32]. The conducting polymers can prevent the aggregation of metal nanoparticles along with easing the electron transfer which increases the sensitivity and selectivity [33]. Among the CPs, polypyrrole (PPy) is one of the most favorable conducting polymers due to excellent redox properties, ease of synthesis, high conductivity, and superior environmental stability [14,15]. The conjugated bonds in the polymer backbone, high electron affinities and low oxidation potential are the fundamental properties of polypyrrole for their unique electrical properties. By a doping process, the conductivity of polypyrrole can be increased which results in the incorporation of counter ions or dopants including inorganic anions and cations, organic molecules, etc. [34]. Polypyrrole’s particular properties such as flexibility, high electrical conductivity and ease of fabrication make it an interesting matrix for composites. Polypyrrole has been favorably electropolymerized as the conducting matrix of composite materials for incorporating noble metals such as Ag, Au, Pt, Ru and Pd [35–39]. In recent years, due to their multifunctional abilities,

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the composites of polypyrrole decorated with metal nanoparticle have thus been drawn a huge attention of several research groups [40,41]. Among the mentioned nanocomposites, the composite of polypyrrole which was decorated with silver nanoparticles (AgNPs) has been constantly investigated since they are effective for various applications [36,42,43]. Excellent catalytic activity for the hydrogen peroxide reduction is one of the important characteristics of the Ag nanoparticles (AgNPs) [44]. Electrochemical data revealed that the presence of silver nanoparticles was responsible for high sensitivity of the modified electrode toward the reduction of H2 O2 [45,46]. Although numerous publications have focused on developing new ways for the preparation of the metal nanoparticles and conducting polymers composites, most of them involved a complicated fabrication method. The preparation for the metal nanoparticlesCP composites with controlled nanostructure in a simple and cost-effective way is still a novel challenge. In the present work, in order to prepare a high sensitive hydrogen peroxide sensor, the electrochemical deposition of polypyrrole–silver nanoparticles (PPy-AgNPs) with increased sensing ability toward hydrogen peroxide (H2 O2 ) is presented. By decorating silver nanoparticles (25 nm) on the surface of polypyrrole, a novel modified electrode based on conducting polymer–metal nanoparticles with intricate structure was formed. The electrochemical properties, morphology, chemical composition and electrocatalytic activity of the prepared polypyrrole decorated with Ag nanoparticles were studied in details. 2. Materials and methods 2.1. Chemicals and reagents Ammonia solution, silver nitrate (99%), potassium permanganate (99%), sulfuric acid (99.99%), sodium hydroxide (98%), hydrochloric acid (38%), hydrogen phosphate potassium (70%), lithium perchlorate (99%), potassium dihydrogen phosphate (99%), pyrrole (99.5%) and hydrogen peroxide (30%) were purchased from Sigma–Aldrich. Before using, pyrrole monomer was distillated. All the chemicals were of analytical grade purity. The solutions were deoxygenated and all the experiments were carried out at room temperature. 2.2. Instruments All the electrochemical measurements including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and chronoamperometry (AMP) were performed using a potentiostat/galvanostat (PGSTAT-302N, Autolab). A working (glassy carbon), reference (saturated calomel) and counter (platinum) electrode formed a three-electrode compartment cell. The EIS measurements were carried out over a frequency ranging from 10 mHz to 100 kHz, with an acquisition of 10 points per decade, and with a signal amplitude of 5 mV around the open circuit potential. EIS data analysis was performed by fitting the experimental results to equivalent circuits using the nonlinear least-square fitting procedure with the chi-squared value minimized to 10−4 . To carry out Fourier transform infrared spectroscopy (FT-IR), a spectrum 400 FT-IR spectrometer was exploited. The composition and structure of the AgNPs-PPy composites were studied using field emission scanning electron microscopes (FESEM) equipped with an energydispersive spectrometer (Quanta 200F). 2.3. Preparation of Ag solution The solution of silver-ammonia [Ag(NH3 )2 OH] was acquired by addition of ammonia (1 wt%) to the silver nitrate (50 mM) solution until the precipitates were completely dissolved. The synthesized

Ag(NH3 )2 OH concentration was around 40 mM [47]. AgNPs solutions were prepared using the solution of [Ag(NH3 )2 OH] at three concentrations i.e. 1 mM, 5 mM and 10 mM, which were then called AgNPs-1, AgNPs-2 and AgNPs-3, respectively. Previously, AgNO3 is used as the source of AgNPs for most nanocomposites [11,48]. To check the effect of using [Ag(NH3 )2 OH] instead of AgNO3 , the solution of AgNPs has been prepared by the concentration of 1 mM which was then labeled as AgNPs-4. 2.4. Fabrication of modified electrode In order to fabricate the nonenzymatic sensor, glassy carbon electrode was chosen to act as the base electrode. To be ready for use, it was dried under high purity of N2 gas flow. A threeelectrode system was used for performing all the electrochemical experiments. A large-area platinum electrode and a 3.0 mm diameter glassy carbon electrode (GCE) were employed as the counter and working electrodes, respectively. By polishing with 1.0 and 0.3 mm alumina powders and rinsing with deionized water before each experiment, the GCE was prepared. 2.5. Preparation of polypyrrole The polypyrrole layer was electrodeposited by amperometric method on the glassy carbon electrode (GCE) at different potential values (0.5–1 V) under high-purity nitrogen atmosphere. The electropolymerization was conducted in a solution containing 0.1 M monomer and 0.1 M LiClO4 . The electrodeposited polypyrrole on the surface of GCE was rinsed with deionized water. Then, in order to eliminate residual monomers and oligomers present in the polypyrrole, the modified electrode was transferred to a monomer-free 0.1 M phosphate buffer solution (PBS) using cyclic voltammetry technique with potential ranging from 0 to 0.8 V at 50 mV s−1 [48]. 2.6. Electrodeposition of silver nanoparticles on the polypyrrole surface Through cyclic voltammetry (CV) method, the electrodeposition of silver nanoparticles on the polypyrrole surface was carried out with the potential ranging from 0.6 to −0.3 V and in Ag(NH3 )2 OH solution at different concentrations (1, 5 and 10 mM). The initial potential for all silver electrodeposition was 0.6 V. AgNPs-PPy was prepared by using solution of Ag(NH3 )2 OH at three different concentrations i.e. 1 mM, 5 mM and 10 mM, which were then nominated to AgNPs-1-PPy, AgNPs-2-PPy and AgNPs-3-PPy, respectively. Previously, AgNO3 was used as the source of silver nanoparticles for most nanocomposites [49,50]. To check the effect of using Ag(NH3 )2 OH instead of AgNO3 , the AgNPs-PPy composite has been prepared by using 0.04 M AgNO3 with the concentration of 1 mM, which was then labeled as AgNPs-4-PPy. 3. Results and discussion A field emission scanning electron micrograph (FESEM) and particle size distribution of the AgNPs-1-PPy, AgNPs-2-PPy, AgNPs3-PPy and AgNPs-4-PPy/GCE are shown in Fig. 1. As depicted in Fig. 1a and b, the AgNPs with an average size of 25 nm and particle size with a narrow distribution have been decorated, uniformly dispersed on the polypyrrole surface and anchored on most parts of the polypyrrole surface. As can be seen in Fig. 1c–f, as the concentration of Ag(NH3 )2 OH increased, the average size of particles increased and consequently the particle size distribution of deposited Ag widened. As previously reported, the size and coverage density of electrodeposited silver nanoparticles on the polypyrrole surface are affected by the types of Ag precursors [51]. The average particle

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Fig. 1. FESEM images and particle size distribution of (a, b) AgNPs-1-PPy/GCE, (c, d) AgNPs-2-PPy/GCE, (e, f) AgNPs-3-PPy/GCE and (g, h) AgNPs-4-PPy/GCE.

size increased to 725 nm and the particle size distribution widened, when AgNO3 was used as a precursor of Ag as shown in Fig. 1g and h. The plausible reason is that Ag(NH3 )2 OH has a higher stability than AgNO3 and has resistance to reduction, preventing the growth of Ag into large particles [47,52].

Fig. 2A (inset) shows the X-ray diffractions of AgNPs-PPy deposited on GCE. As can be seen, a broad peak exists at 24–27◦ , due to the periodically aligned polypyrrole chains [53]. The intense peaks at 38.3◦ , 44.2◦ , 64.4◦ , and 77.5◦ correspond to (1 1 1), (2 0 0) and (2 2 0) planes of cubic phase of silver, respectively [47,54]. The

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Fig. 2. (A) EDX spectra of AgNPs-1-PPy/GCE and (inset) XRD spectrum of AgNPs-1-PPy/GCE. (B) Cyclic voltammograms of (a) AgNPs-1-PPy/GCE, (b) AgNPs-2-PPy/GCE, (c) AgNPs-3-PPy/GCE, (d) AgNPs-4-PPy/GCE in the presence of 1 mM H2 O2 in phosphate buffer solution (pH 6.5) at scan rates of 50 mV s−1 and (e) Ppy/GCE. (C) Nyquist plots of (a) AgNPs-1-PPy/GCE, (b) AgNPs-2-PPy/GCE, (c) AgNPs-3-PPy/GCE and (inset) equivalents circuits. (D) (a) AgNPs-1-PPy/GCE, (b) AgNPs-2-PPy/GCE, (c) AgNPs-3-PPy/GCE and (inset) equivalents circuits.

diffractograms of AgNPs-PPy composites presented the peaks due to the existence of PPy and silver nanoparticles. EDX analysis was employed to prove the elemental composition of Ag nanoparticles on the surface of PPy. Fig. 2A displays the EDX spectra of AgNPs-1-PPy/GCE. Elemental Ag is detected in AgNPsPPy/GCE. This supports the point that Ag was able to be successfully deposited onto PPy nanofibers. High electrocatalytic activity for the reduction of H2 O2 is one of the most promising characteristics of AgNPs. In order to investigate the electrochemical performance of nonenzymatic AgNPs electrodeposited on the surface of polypyrrole, CV of all AgNPs-PPy/GCE electrodes was carried out in a 0.1 M phosphate buffer solution (PBS) at pH 6.5 in the presence and absence of 1 mM hydrogen peroxide. For the PPy/GC electrode (Fig. 2B(e)), no electrochemical activity was recorded under the presence of hydrogen peroxide at the selected potential range. When silver nanoparticles are electrodeposited on the surface of PPy, the modified electrodes show a remarkable electrocatalytic behavior toward H2 O2 reduction. PPy decorated with AgNPs is different from individual PPy, not only in the synergistic amplification effect between PPy and AgNPs but also in the electrocatalytic reduction effect of Ag toward hydrogen peroxide. Fig. 2B(a, d) shows the CVs of AgNPs-1-PPy electrode in the presence and absence of 1 mM H2 O2 at a scan rate of 50 mV s−1 . In the absence of H2 O2 , a little reduction peak occurred at about 0.15 V at AgNPs-1-PPy-GC electrode (Fig. 2B(d)). When H2 O2 was added in the solution, the reduction peak increased dramatically, suggesting that AgNPs-1-PPy/GCE exhibited high electrocatalytic activity toward the reduction of H2 O2 . Therefore, a highly increased

reduction peak at AgNPs-1-PPy-GC electrode in the presence of H2 O2 revealed the synergistic effect of Ag and polypyrrole which can greatly improve the electrocatalytic reduction of H2 O2 . With increasing the concentration of Ag(NH3 )2 OH solution, the particle size increased and consequently the agglomeration takes place which causes to reduce the reduction of H2 O2 . Finally, it can be concluded that after addition of H2 O2 to the solution, silver nanoparticles which are decorated on the surface of the PPy surface react chemically with H2 O2 according to the following equations: 2Ppy-AgNPs(0) + H2 O2 → 2Ppy-AgNPs(I)-OH +

−

2Ppy-AgNPs(I)-OH + 2H + 2e → 2Ppy-AgNPs(0) + 2H2 O

(1) (2)

In the phosphate buffer solution, the H2 O2 was reduced via following mechanism: H2 O2 + e− ↔ OH + OH−

(3)

OH + e− ↔ OH−

(4)

2OH− + 2H+ ↔ 2H2 O

(5)

After electrodepositing of the AgNPs on the surface of PPy, as shown below, the reduction of H2 O2 becomes more irreversible: Ag 1 H2 O2 −→ O2 + H2 O 2 Electrode

O2 + 2e− + 2H+ −→ H2 O2

(6) (7)

Then, the generated O2 would turn into the detection signal on electrode suggesting that the electrochemical reduction of O2 on

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Table 1 EIS parameters achieved by equivalent circuits modified electrodes in 0.1 M KCl solution containing 1 mM Fe(CN)6 3−/4− (1:1). Electrode

Rs ()

Rct ()

Q (␮Mho)

W (mMho)

n

AgNPs-1-Ppy AgNPs-2-Ppy AgNPs-3-Ppy

185 199 210

1423 689 140

130 84 1.01e+03

3.35 6.32 4.08

0.53 0.55 0.45

the electrode occurs [46,55]. Due to a low applied potential, the background current decreased, which can minimize the response of common interference species and reduce the O2 reduction current [46]. In order to analyze the impedance changes of the modified electrode, electrochemical impedance spectroscopy was employed. Fig. 2C depicts the Nyquist plots in 0.1 M KCl solution containing 1 mM Fe(CN)6 3−/4− (1:1). The Nyquist plot of impedance spectra consists of semicircle portion which at higher frequencies correlates to the electron transfer limited process, while on the other hands, a linear portion at lower frequencies correlates to the diffusion process. The electron transfer resistance (Rct ) can be evaluated by using the diameter of the semicircle diameter. As previously discussed, with increasing the concentration of Ag(NH3 )2 OH solution, the size of the electrodeposited AgNPs increased and consequently, agglomeration takes place. Moreover, with increasing the density of electrodeposited AgNPs, the charge transfer resistance (Rct ) of

the modified electrodes decreases. This can be attributed to the low resistance properties of AgNPs. The comparison between the semicircle diameters from the Nyquist diagrams of AgNPs-1-PPy (1423 ), AgNPs-2-PPy (689 ) and AgNPs-3-PPy (140 ) shows the direction of Rct : GCE > AgNPs-1-PPy > AgNPs-2-PPy > AgNPs-3-PPy In order to figure out the impedance parameters, the NOVA software is employed in the simulations. The Rs (CPE[Rct W]) equivalent circuit model was employed in the simulation of the impedance behavior of all the modified electrodes, from the experimentally gained impedance data. By exploiting the series components, the model was developed. The first component is ohmic resistance of the solutions (Rs ) and the second one is a set of constant phase elements (CPE) and the resistance of layer (Rct ). Rct indicates the conductivity of the samples that are in the parallel position with CPE. Additionally, from the diffusion impedance, W which stands

Fig. 3. (a) Current–time responses of AgNPs-1-PPy/GCE with the subsequent addition of H2 O2 into 0.1 M PBS (pH 6.5) at 0.025 V. (Inset) Effect of the applied potential on the current response of 1 mM H2 O2 on the AgNPs-1-PPy/GCE in 0.1 M PBS (pH 6.5). (b) Long term stability of the AgNPs-1-PPy/GCE studied in 3 weeks, and (inset) shows amperometric response of AgNPs-1-PPy/GCE upon the successive addition of 1 mM uric acid, glucose, ascorbic acid, and fructose into 0.1 M PBS (pH 6.5) with an applied potential +0.025 V. Calibration curve of (c) lower (0.1–5 mM) and (inset: calibration curve) and (d) higher (10–120 mM) concentration range.

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Table 2 H2 O2 determination in real samples. Sample number

Added (mM)

SD

RSD%

Measured by biosensor (mM)

Recovery%

1 2 3 4 5

0.1 1 5 10 50

0.000811 0.02085 0.2948 0.1083 0.8238

0.810 1.655 6.296 1.890 1.517

0.097 0.964 5.129 9.605 48.628

97.45 96.48 102.58 96.05 97.25

for the Warburg element is a series connection to Rct (Table 1). Fig. 2D shows the phase plot that is in agreement with the results obtained from Nyquist plot.

of quantification (LOQ) and the limit of detection (LOD) of AgNPs1-PPy/GCE were determined by using the following equations: LOQ =

10SB b

(8)

3.1. Sensor optimization

LOD =

3SB b

(9)

The mentioned experimental results confirm that H2 O2 can electrochemically be reduced in the presence of AgNPs-1-PPy on the surface of GCE. To develop the performance of the sensor, various factors influencing the current response of the sensor were investigated. Fig. 3a (inset) shows the influence of operating potential on the amperometric response of the AgNPs-1-PPy and the reduction current studied under batch conditions ranging from 0.0 to 0.1 V in a solution containing 1 mM H2 O2 in 0.1 M phosphate buffer solution (pH 6.5). As can be seen, the potential value of 0.025 V was determined as the operating potential.

where b is the slope of the calibration curve and SB is the standard deviation of the blank solution and, as shown in Fig. 3c and d for two linear parts, the LOD and LOQ (S/N = 3) were calculated to be 0.115 ␮M, 0.383 ␮M and 0.256 ␮M, 0.854 ␮M, respectively. As listed in Table 3, the detection limit and the linear range of AgNPs-1-PPy are better and wider than other modified electrodes based on polypyrrole and silver nanoparticles. The main reason for these excellent properties is the synergistic effect of PPy and silver nanoparticles which can intensively improve the electrocatalytic reduction of H2 O2 . Moreover, AgNPs can intensively increase the electron transfer reactivity of the AgNPs-1-PPy-GC electrode, thus the H2 O2 reduction is accelerated by the catalyst effect of AgNPs [56,57]. Additionally, Welch et al. revealed that the H2 O2 reduction could be accelerated by incorporating the smaller nanosized silver particles [44]. Nanosized silver particles provide a huge available surface area for reduction of H2 O2 .

3.2. Amperometric detection of H2 O2 Amperometric i–t curve is the regularly utilized technique to assess the electrocatalytic activities of electrochemical sensors. Fig. 3a (inset) shows the amperometric responses of the AgNPs-1PPy/GC electrode at 0.025 V versus SCE as a result of the successive addition of H2 O2 to the continuously stirred 0.1 M phosphate buffer solution (pH 6.5) at 25 ◦ C. The experiments were carried out with freshly prepared electrode. As shown in Fig. 3a, the AgNPs-1PPy/GCE was very sensitive to the changes in the concentration of H2 O2 and responded rapidly. The response time was fast (less than 2 s) and with increasing the concentration of H2 O2 from 0.1 mM to 120 mM, the current increased linearly. In calibration curve, the sensor shows two linear sections for the response to H2 O2 . Based on the first linear section, the linear regression equation of I = 62.6 (␮A mM−1 ) + 260.6 (R2 = 0.999) is determined, increasing from 0.1 mM to 5 mM (Fig. 3b), while in a higher concentration of H2 O2 , the second linear section raised up to 120 mM (Fig. 3c) with a linear equation of I = 28.1 (␮A mM−1 ) + 402.7 (R2 = 0.999). The limit

3.3. Repeatability, reproducibility and stability The repeatability, reproducibility and stability of the prepared sensor were studied. Five modified electrodes were prepared under the same condition and relative standard deviation (RSD) of the current response toward 1 mM H2 O2 was found to be 3.5%, confirming that the results can be reproducible. The repeatability of one sensor to determine 1 mM H2 O2 was fairly good. The RSD was 4.23% for 10 successive assays. In order to investigate the stability of AgNPs-1-PPy electrode, the modified electrode was stored in ambient condition and the current was periodically monitored for 21 days (Fig. 3b). The current response did not have considerable decrease by the first week, and as can be seen from Fig. 3b, the sensor retains around 89% of its initial response after 3 weeks (I0 and I are the response current in the first and following days,

Table 3 Comparison between LOD and linear range of different nonenzymatic H2 O2 sensors. Modify electrode

Performance −1

LOD (␮mol l Ag NPs-NFs/GCE AgNP/rGO-benzylamine ERGO-Ag/GCE PPy/Mn NWs Ag NPs-MWCNT/Au PQ11-AgNPs/GCE Graphene–AgNPLs Ag NPs/PPy/Fe3 O4 /GCE PDDA-rGO/AgNPs/GCE AgNP–CPNBs AgNPs-1-PPy/GCE

62 31.3 1.6 2.12 0.5 33.9 3 1.7 35 0.9 0.115 0.256

References )

Liner range (mmol−1 ) 0.1–80 0.1–100 0.1–100 0.005–0.09 0.05–17 0.1–180 0.02–10 0.005–11.5 0.1–41 0.1–70 0.1–5 10–120

[53] [54] [44] [55] [33] [56] [57] [37] [44] [58] This work

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respectively). The overall performance concluded that AgNPs-1PPy shows a good repeatability, reproducibility and stability. 3.4. Interference study Fig. 3b (inset) demonstrates the selectivity and anti-interference advantages by comparing the amperometric responses of relevant electroactive species. The amperometric response of the AgNPs-1PPy toward the successive addition of 1 mM H2 O2 was measured and this is followed by glucose, ascorbic acid, ethanol and uric acid into 0.1 M PBS at pH 6.5 at a working potential of 0.025 V. As can be seen, the current response of the mentioned electroactive interfering species is quite negligible which confirms that AgNPs-1-PPy has a superior selectivity toward H2 O2 . The good ability of antiinterference is largely attributed to the low working potential of 0.025 V used in the determination of H2 O2 [58]. To prove the accuracy of the sensor, a lens-cleaning solution was used for performing the detection of H2 O2 . The H2 O2 determination in the samples of the mentioned solution was carried out on the modified sensor employing standard addition method. The dilution of samples has been done through using phosphate buffer solution (pH 6.5) prior to determining the current response. Later, H2 O2 solutions were successively added to the system in order to determine the current response through standard addition method. All the measurements were carried out four times. Table 2 lists the average recoveries. According to Table 2 and considering the relative standard deviation (RSD) values and calculated recovery, it can be observed that the developed sensor holds possible applications for evaluating specific concentration range of H2 O2 . 4. Conclusion AgNPs-1-PPy/GCE has been successfully prepared via an in situ electrochemical deposition process. XRD, FT-IR, EDX and EIS results confirmed the presence of AgNPs and PPy. The FESEM images of the modified electrode revealed that PPy and AgNPs were uniformly formed and PPy was decorated with small particle size of AgNPs (25 nm). The electrochemical behavior of GCE coated with the AgNPs-1-PPy/GCE film showed the highest electrocatalytic activity as compared with other modified GCEs. AgNPs-1-PPy/GCE electrochemical sensor had a wide linear range up to 120 mM H2 O2 concentration, a high sensitivity and a low detection limit of 0.115 and 0.256 ␮M. These great performances, including high selectivity and sensitivity, easy fabrication and especially wide linear range, make AgNPs-1-PPy/GCE an excellent amperometric sensor for determining H2 O2 concentration. Acknowledgments Pooria Moozarm Nia wishes to thank Mahtab Mahdavifar for precious reviews and Dr. Mehrdad Gholami and Dr. Farnaz Lorestani for their help and support. This research is supported by High Impact Research MoE Grant UM.C/625/1/HIR/MoE/SC/04 from the Ministry of Education Malaysia, UMRG Program RP012A-14SUS, PRGS grant PR0022014A and University Malaya Centre for Ionic Liquids (UMCiL). References [1] E.A. Veal, A.M. Day, B.A. Morgan, Hydrogen peroxide sensing and signaling, Mol. Cell 26 (2007) 1–14, http://dx.doi.org/10.1016/j.molcel.2007.03.016. [2] K. Zhang, Stopped-flow spectrophotometric determination of hydrogen peroxide with hemoglobin as catalyst, Talanta 51 (2000) 179–186, http://dx. doi.org/10.1016/S0039-9140(99)00277-5. [3] E.C. Hurdis, H. Romeyn, Accuracy of determination of hydrogen peroxide by cerate oxidimetry, Anal. Chem. 26 (1954) 320–325, http://dx.doi.org/10.1021/ ac60086a016.

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