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Non-enzymatic electrochemical

sensing of hydrogen peroxide based

on Polyaniline-MnO2 nanofibers

modified electrode

- i -

CONTENT

List of Table ⅲ

List of Figures ⅳ

Abstract ⅵ

Non-enzymatic electrochemical sensing of hydrogen peroxide based on Polyaniline-MnO2

nanofibers modified electrode

1. Introduction 2

2. Experimental 5

2.1. Chemicals and reagents 5

2.2. Apparatus and measurements 5

2.3. Synthesis of PANI nanofibers 6

2.4. Synthesis of PANI-MnO2 nanofibers 6

2.5. Electrode modification 7

- ii -

3. Results and Discussion 8

3.1. Characterization of the synthesized PANI and PANI-MnO2

nanofibers 8

3.2. Electrochemical impedance spectroscopy (EIS) characterization 12

3.3. Voltammetric behaviors of H2O2 at PANI-MnO2/GCE 14

3.4. Amperometric response of H2O2 at PANI-MnO2/GCE 21

3.5. Selectivity, reproducibility, and stability 25

4. Conclusions 27

5. References 28

- iii -

List of Table

Table 1. Electroanalytical characteristics of various modified electrodes

toward hydrogen peroxide. 24

- iv -

List of Figures

Figure 1. SEM images of (A) PANI, (B) PANI-MnO2 nanofibers, and

(C) XRD pattern of PANI-MnO2 nanofibers. 9

Figure 2. (A) XPS survey spectra of PANI, and PANI-MnO2, (B) XPS

spectrum of the Mn 2p core level at a higher resolution. 11

Figure 3. Nyquist plots of (a) bare GCE, (b) PANI/GCE, and (c)

PANI-MnO2/GCE in 0.1 M PBS (pH 7.4) containing 5 mM [Fe(CN)6]3－

and 5 mM [Fe(CN)6]4－. 13

Figure 4. CVs of (a) bare GCE, (b) PANI/GCE, and (c)

PANI-MnO2/GCE in N2-saturated 0.1 M PBS (pH 7.4) containing 1 mM

H2O2 at a scan rate of 50 mV s-1. 15

Figure 5. CVs of PANI-MnO2/GCE in (a, b) N2-saturated, and (c)

O2-bubbled 0.1 M PBS (pH 7.4) in the (a, c) absence and (b) presence

of 1 mM H2O2 at a scan rate of 50 mV s-1. Inset: Magnified plot of

curve a. 17

- v -

Figure 6. CVs of PANI-MnO2/GCE in N2-saturated 0.1 M PBS (pH

7.4) in the presence of H2O2 with different concentrations (from a to e:

1, 2, 3, 4, and 5 mM) at a scan rate of 50 mV s-1. Inset: plot of the

cathodic peak current versus the H2O2 concentration. 19

Figure 7. CVs of PANI-MnO2/GCE in N2-saturated 0.1 M PBS (pH

7.4) in the presence of 1 mM H2O2 at different scan rates (from a to

j: 20, 40, 60, 80, 100, 120, 140, 160, 180, 200 mV s-1). Inset: plot of

the cathodic peak current of H2O2 versus the scan rate. 20

Figure 8. (A) Amperometric response of PANI-MnO2/GCE on

successive injections of H2O2 into stirred N2-saturated 0.1 M PBS (pH

7.4) at -0.4 V. (B) The corresponding calibration curves of the current

response versus H2O2 concentration. Inset: calibration curve in the lower

concentration region (from 5 M to 50 M). μ μ 23

Figure 9. Amperometric response of PANI-MnO2/GCE on successive

injections of H2O2, AA, UA, L-Cys, and glucose (each at 0.1 mM) in

N2-saurated 0.1 M PBS (pH 7.4) at 0.4 V. – 26

- vi -

Abstract

Non-enzymatic electrochemical sensing of hydrogen peroxide based

on Polyaniline-MnO2 nanofibers modified electrode

Jong-Hyeok LeeChemistry Education Major

Department of Science EducationThe Graduate School

Seoul National University

In this study, we synthesized polyaniline-manganese dioxide (PANI-MnO2)

nanofibers and investigated an electrochemical application of the

determination of the hydrogen peroxide (H2O2) level. PANI-MnO2

nanofibers were synthesized by a one-step mixing process from a

prepared PANI nanofibers aqueous dispersion and a KMnO4 aqueous

- vii -

solution. The morphology and chemical composition of the synthesized

PANI-MnO2 nanofibers were characterized by field-emission scanning

electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS),

and X-ray diffraction (XRD). Subsequently, we fabricated a facile

electrochemical hydrogen peroxide sensor based on a PANI-MnO2

modified glassy carbon electrode (PANI-MnO2/GCE) by a drop-casting

method, and its electrochemical behavior was investigated using

electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV),

and amperometry. The results clearly exhibited the good electrocatalytic

activity of the PANI-MnO2/GCE toward H2O2 reduction in pH 7.4

phosphate buffer solution (PBS). The non-enzymatic H2O2 sensor

displayed a wide linear range (5-50 M and 0.05-10 mM), a low μ

detection limit (0.8 M at S/N=3), high sensitivity (403.3 and 152.1 A μ μ

mM-1 cm-2), and negligible interference from ascorbic acid, uric acid,

L-cysteine and glucose at an applied potential of -0.4 V (vs. Ag/AgCl).

Key words: Hydrogen peroxide, Manganese dioxide,

Polyaniline, Amperometry, Sensor

Student Number : 2012-21433

- 1 -

Non-enzymatic electrochemical

sensing of hydrogen peroxide based

on Polyaniline-MnO2 nanofibers

modified electrode

- 2 -

1. Introduction

Hydrogen peroxide (H2O2) is not only the most commonly used

oxidizing agent in many fields, but it is also naturally produced by

living organisms as a by-product of oxidative metabolism. It is

therefore one of the most important analytes in pharmaceutical, clinical,

environmental, and food manufacturing applications [1]. Various

techniques for an accurate determination of H2O2 levels have been

studied, such as titrimetry [2], chemiluminescence [3], fluorescence [4],

and spectrophotometry [5]. Among these techniques, the electrochemical

approach has attracted extensive attention due to its instrumental

simplicity, moderate cost, portability, and possibility for real-time

detection [6]. For instance, electrochemical sensors based on enzymes

such as horseradish peroxidase [7], catalase [8], cytochrome c [9], and

hemoglobin [10] show high selectivity and sensitivity for H2O2

determinations. However, enzyme-based sensors are unstable, relatively

expensive to manufacture, and highly sensitive to environmental

conditions [11]. Consequently, many researchers have studied the

development of non-enzymatic electrochemical H2O2 sensors using

various inorganic nanomaterials. In particular, transition metal oxides are

very promising as electrocatalysts for H2O2 determination because they

are active, inexpensive, and thermodynamically stable [12]. For example,

copper oxide [13], iron oxide [14], cadmium oxide [15], and zinc oxide

[16] modified electrodes display high sensitivity, low detection limits,

and rapid response for H2O2 determination.

In recent years, manganese dioxide has been widely used as an

- 3 -

electrode material for H2O2 determination [17 27] owing to its excellent –

catalytic activity toward the decomposition of hydrogen peroxide [28]

and the fact that it is an environmentally friendly material [29].

However, the poor intrinsic electronic conductivity [30] is the main

problem associated with a performance improvement of the MnO2-based

electrochemical sensors. Furthermore, since MnO2 dissolution reaction is

facilitated by not only proton insertion, but also by a negative potential

[31], the operating conditions of several MnO2-based electrochemical

H2O2 sensors are restricted under a strong alkaline medium condition

[26] in a high positive potential region [17 24]. In particular, at a –

positive working potential, oxidizable substances which exist in the

blood, such as ascorbic acid and uric acid, can interfere with the H2O2

determination. To offset these shortcomings of MnO2, various

conducting materials, such as noble metal nanoparticles and carbon

nanomaterials, have been applied during the fabrication of the

MnO2-based electrochemical H2O2 sensors [18,23,25 27]. Among these –

conducting nanomaterials, polyaniline (PANI), which is one of the most

commonly studied conducting polymers, is a promising material for

chemical sensors owing to its facile synthesis, environmental stability,

and simple acid/base doping/dedoping chemistry [32]. Moreover, the

emeraldine salt produced from doping an emeraldine base with an acid,

i.e., the half-oxidation state of PANI, shows high electrical conductivity

such that the salt is a good candidate for an electrochemical sensor

[33]. However, the electrical conductivity of PANI depends on the

proton concentration because the acid-doping of PANI results from its

protonation. Hence, its main disadvantage for use as an electrochemical

- 4 -

sensor is a great decrease in its electrical conductivity above pH 4. For

this reason, doping PANI samples with metals or metal oxides, such as

gold nanoparticle-doped PANI [34], has been widely researched,

showing good electrocatalytic activity at a neutral pH.

Along these lines, the synergetic effect of a combination of MnO2

and PANI will be promising and fascinating for application to

electrochemical sensors to determinate H2O2. Recently, a study reported

H2O2 sensing at glassy carbon electrode modified by MnO2-carbonized

nanostructured polyaniline in a pH 7 phosphate buffer solution (PBS)

[35], but it was operated at a very high anodic applied potential (+0.75

V vs. saturated calomel electrode). Moreover, there were no discussions

about the sensitivity, linear range, or the effects of interfering

contaminants such as ascorbic acid.

To the best of our knowledge, there are rare reports on the

application of electrochemical H2O2 sensor based on conducting

polymer-MnO2 at a cathodic applied potential. In this study, we

synthesized uniform PANI-MnO2 nanofibers using prepared PANI

nanofibers aqueous dispersion and KMnO4 aqueous solution by one-step

mixing method. Then, fabricated PANI-MnO2 nanofibers modified GCE

as electrochemical sensor to determinate H2O2. It exhibited good

electrocatalytic activity toward the reduction of H2O2 at pH 7.4.

Moreover it displayed wide linear range, low detection limit, high

sensitivity, and negligible interference from ascorbic acid, uric acid,

L-cysteine and glucose.

- 5 -

2. Experimental

2.1. Chemicals and reagents

Hydrogen peroxide (H2O2, 30 wt. % in H2O), potassium

permanganate (KMnO4), aniline (C6H5NH2), ammonium persulfate

((NH4)2S2O8, APS), potassium ferricyanide (K3Fe(CN)6), potassium

ferrocyanide (K4Fe(CN)6), Nafion (~5% in a mixture of lower aliphatic

alcohols and water), ascorbic acid, uric acid and glucose were

purchased from Sigma-Aldrich Co. (USA). L-cysteine was purchased

from Yakuri Pure Chemicals Co. (Japan). Hydrochloric acid was

obtained from Daejung Chemicals Co. (Korea). Methylene chloride was

purchased from J.T. Baker (USA). 0.1 M phosphate buffer solution

(PBS) was prepared by mixing stock solutions of dipotassium hydrogen

phosphate (K2HPO4) and monopotassium phosphate (KH2PO4), both of

which were obtained from Junsei Chemical Co. (Japan). All chemicals

were of analytical reagent grade and were used without further

purification. All solutions were prepared with deionized water (DIW)

obtained from an ultra-pure water purification system (Human Co.,

Korea) with a resistivity of not less than 18.2 M cm. All Ω

measurements were carried out at room temperature.

2.2. Apparatus and measurements

The electrochemical experiments were conducted using a CHI Model

- 6 -

842B (C.H. Instruments, Inc., USA) device with a conventional

three-electrode cell. The working electrode was a bare or modified

glassy carbon electrode (GCE, 3mm in diameter). The counter and

reference electrodes used were a platinum wire and an Ag/AgCl

electrode filled with 3 M KCl, respectively. The synthesized nanofibers

were characterized by FE-SEM (S-4800, Hitachi, Japan), XPS (AXIS−

Hsi, Kratos Inc., Japan), and XRD (New D8-Advance, Bruker, China).

All ultrasonic cleaning was done using a US-2510 Ultrasonic Cleaner

(Branson, USA).

2.3. Synthesis of PANI nanofibers

Polyaniline nanofibers were prepared using an interfacial

polymerization method [36]. An amount of 3.2 mmol of aniline was

dissolved in 10 mL of methylene chloride. Ammonium persulfate (0.8

mmol) was dissolved in 10 mL of 1 M HCl, after which the prepared

aniline solution was added to a 20 ml glass vial, and HCl acid solution

was then slowly added with a dropping pipette. In about an hour, the

polymerization reaction was complete and an aqueous layer turned dark.

Subsequently, 6 mL of the aqueous solution was centrifuged, filtered,

washed with DIW several times and dried in an oven at 40 °C for 12 h.

2.4. Synthesis of PANI-MnO2 nanofibers

The PANI-MnO2 nanofibers were synthesized according to the

- 7 -

reported method with a slight modification [37]. In a typical procedure,

5 mg of the as-synthesized PANI nanofibers were dispersed in 2.5 mL

of DIW. Then, 2.5 mL of a 0.07 M KMnO4 aqueous solution was

added to the above suspension while stirring for an hour. The

precipitation was then washed with ethanol and DIW by centrifugation

at 4000 rpm for 15 min and re-dispersed into 5 mL of DIW.

2.5. Electrode modification

A glassy carbon electrode was polished with aqueous slurries of

successively finer alumina powders (particle size: 0.3 and 0.05 m) on μ

a polishing pad. The GCE was washed and then sonicated in deionized

water for 2 min. After the electrode was dried under a gentle stream

of N2 gas, 6 L of this PANI-MnOμ 2 dispersion was dropped onto a

purified GCE surface and dried in an oven at 40 °C for an hour. Next,

6 L of Nafion (0.5 wt % in ethanol) was also placed on the above μ

electrode surface and dried in an oven at 40 °C, again for an hour.

- 8 -

3. Results and Discussion

3.1. Characterization of the synthesized PANI and

PANI-MnO2 nanofibers

The morphologies of the PANI and PANI-MnO2 nanofibers were

characterized by field-emission scanning electron microscopy (FE-SEM),

as shown in Fig. 1. As shown in Fig. 1A, the average diameter of the

uniform PANI nanofibers was about 65 nm. After the MnO2 coating

process, the structures of the nanofibers were well preserved and the

average diameter of the PANI-MnO2 nanofibers was about 105 nm,

showing an increase of about 60 percent (Fig. 1B). This indicated that

the PANI nanofibers acted as a substrate for the growth of the MnO2

layer. Additionally, these average diameters of the PANI-MnO2

nanofibers are relatively small compared to recent reports with respect

to applications of other PANI-MnO2 nanofibers [37,38]. Hence, the

surface-area-to-volume ratio and the active sites of the PANI-MnO2

could be larger, giving it an advantage for signal enhancement as an

electrode nanomaterial for electrochemical sensing. Fig. 2C shows the

X-ray diffraction (XRD) pattern of the PANI-MnO2 nanofibers.

According to earlier research, the peaks of the XRD pattern are

indexed to monoclinic K birnessite MnO− 2 (JCPDS No. 80-1098), which

consists of 2D edge-sharing MnO6 octahedral layers with K+ cations

and water molecules in the interlayer space [37].

- 9 -

Figure 1. SEM images of (A) PANI, (B) PANI-MnO2 nanofibers, and

(C) XRD pattern of PANI-MnO2 nanofibers.

- 10 -

To investigate the chemical composition of the synthesized nanofibers

and the oxidation state of manganese, they were examined by X-ray

photoelectron spectroscopy (XPS). As shown in Fig. 2A, Mn 2p peaks

appeared after the MnO2 coating of PANI, indicating that MnO2 was

immobilized on the PANI nanofiber surface. The high-resolution Mn 2p

core-level spectrum (Fig. 2B) shows that Mn 2p3/2 and Mn 2p1/2 peaks

have binding energies centered at 641.5 eV and 653.3 eV, respectively.

The spin-energy separation is 11.8 eV, and these results coincide with

the reported data of MnO2 [39,40].

- 11 -

Figure 2. (A) XPS survey spectra of PANI, and PANI-MnO2, (B) XPS

spectrum of the Mn 2p core level at a higher resolution.

- 12 -

3.2. Electrochemical impedance spectroscopy (EIS)

characterization

Electrochemical impedance spectroscopy (EIS) provides important

information about the interfacial properties of electrodes [41]. Nyquist

plots of bare GCE, PANI/GCE, and PANI-MnO2/GCE in 0.1 M PBS

(pH 7.4) containing 5 mM [Fe(CN)6]3－ and 5 mM [Fe(CN)6]4－ at

+0.22 V (vs. Ag/AgCl) are displayed in Fig. 3. Generally, the

semicircle diameter of the Nyquist plot is equal to the electron transfer

resistance (Rct). As shown, the Rct values of the bare GCE (curve a)

and the PANI/GCE (curve b) were about 100 and 200 , respectively. Ω

After PANI-MnO2 was modified on the GCE, however, Rct dramatically

increased to about 1200 , owing to the presence of semiconductive Ω

MnO2. Consequently, the PANI-MnO2 nanofibers were well immobilized

on the GCE.

- 13 -

Figure 3. Nyquist plots of (a) bare GCE, (b) PANI/GCE, and (c)

PANI-MnO2/GCE in 0.1 M PBS (pH 7.4) containing 5 mM [Fe(CN)6]3－

and 5 mM [Fe(CN)6]4－.

- 14 -

3.3. Voltammetric behaviors of H2O2 at PANI-MnO2/GCE

We investigated the electrocatalytic activity of PANI-MnO2 for H2O2

determination by cyclic voltammetry. Fig. 4A displays the cyclic

voltammograms (CVs) of bare GCE, PANI/GCE, and PANI-MnO2/GCE

in N2-saturated 0.1 M PBS (pH 7.4) containing 1 mM H2O2. The

MnO2/GCE was fabricated using an electrodeposition method [24] for

comparison, but the MnO2 layer dissolved from GCE surface in this

working condition. At a negative potential, MnO2 dissolution may be

facilitated due to the reduction of Mn(IV) to Mn(III) [31]; therefore,

we could not obtain reproducible data. As shown in Fig. 4, the bare

GCE showed no significant electrochemical response (curve a). For the

PANI/GCE, broad anodic current peak around -0.15 V was observed

(curve b). It is due to the sum of the two transitions from

leucoemeraldine to emeraldine state and from emeraldine to

pernigraniline state [42], but is not related to the redox of H2O2.

However, PANI-MnO2/GCE displayed a high cathodic current peak of

about 30 A at -0.45 V (curve c). This results show that, unlike bare μ

GCE and PANI, PANI-MnO2 has excellent electrocatalytic activity

toward a reduction of H2O2.

- 15 -

Figure 4. CVs of (a) bare GCE, (b) PANI/GCE, and (c)

PANI-MnO2/GCE in N2-saturated 0.1 M PBS (pH 7.4) containing 1

mM H2O2 at a scan rate of 50 mV s-1.

- 16 -

According to earlier study, MnO2 has the catalytic properties of not

only H2O2 decomposition, but also O2 reduction [43]. Fig. 5 shows that

an oxygen reduction reaction (ORR) occurred at the surface of the

PANI-MnO2/GCE in the presence of H2O2. There was no cathodic

current peak in N2-saturated PBS in the absence of H2O2 (curve a, and

the inset in Fig. 5), while a high cathodic current peak appeared in

O2-bubbled PBS in the absence of H2O2 (curve c). Its peak potential

coincides with that in 1 mM H2O2 in N2-saturated PBS (curve b) at

-0.45 V, and the CV shapes are very similar. Most likely, the detection

signal is caused by the following processes. First, H2O2 is decomposed

into H2O and O2 by MnO2 [28]. The generated O2 is then reduced at

the surface of the electrode via the mechanism shown below:

→

(1)

→

(2)

Overall reaction: → (3)

O2 is reduced to HO2－ (reaction 1) and MnO2 facilitates HO2

－

disproportionation (reaction 2). The process consequently increases the

conversion efficiency of an overall four-electron reduction of O2 to OH－

(reaction 3) [44] such that the reduction of the H2O2 current increases

remarkably at the PANI-MnO2/GCE.

- 17 -

Figure 5. CVs of PANI-MnO2/GCE in (a, b) N2-saturated, and (c)

O2-bubbled 0.1 M PBS (pH 7.4) in the (a, c) absence and (b) presence

of 1 mM H2O2 at a scan rate of 50 mV s-1. Inset: Magnified plot of

curve a.

- 18 -

Fig. 6 displays the cyclic voltammograms of PANI-MnO2/GCE in

N2-saturated 0.1 M PBS (pH 7.4) with different concentrations of H2O2.

This result shows the effect of the H2O2 concentration on the current.

The cathodic current peak was gradually increased with each H2O2

injection, showing a linear relationship with the H2O2 concentration with

a correlation coefficient of 0.9920 (inset in Fig. 6). Fig. 7 shows the

correlation between the current and the scan rate. The cathodic peak

current was increased with an increase in the scan rates from 20 to

200 mV s-1 in proportion to the scan rate with a correlation coefficient

of 0.9965 (inset in Fig. 7). This result indicates that the electrocatalytic

reaction is adsorption-controlled.

- 19 -

Figure 6. CVs of PANI-MnO2/GCE in N2-saturated 0.1 M PBS (pH

7.4) in the presence of H2O2 with different concentrations (from a to e:

1, 2, 3, 4, and 5 mM) at a scan rate of 50 mV s-1. Inset: plot of the

cathodic peak current versus the H2O2 concentration.

- 20 -

Figure 7. CVs of PANI-MnO2/GCE in N2-saturated 0.1 M PBS (pH

7.4) in the presence of 1 mM H2O2 at different scan rates (from a to

j: 20, 40, 60, 80, 100, 120, 140, 160, 180, 200 mV s-1). Inset: plot of

the cathodic peak current of H2O2 versus the scan rate.

- 21 -

3.4. Amperometric response of H2O2 at PANI-MnO2/GCE

Fig. 8A displays the amperometric response of PANI-MnO2/GCE

upon successive injections of H2O2 into stirred N2-saturated 0.1 M PBS

(pH 7.4) at an applied potential of -0.4 V. The signal showed a rapid

response to the injection of H2O2 and reached a steady-state current

quickly. The fast amperometric response is ascribed to the excellent

electrocatalytic activity of MnO2 and to the electric conductivity of

PANI toward the reduction of H2O2, though MnO2 is intrinsically a

poor electronic conductor. The corresponding calibration curves of the

current response are shown in Fig. 8B. As shown, the linear response

region is divided into two parts. This result is similar to that of

previously reported Au-MnO2-rGO modified GCE [27]. The sensitivities

of the sensor are 403.3 A mMμ -1 cm-2 in the lower concentration

region with a correlation coefficient of 0.9994 (inset in Fig. 8B, from 5

M to 50 M), and 152.1 A mMμ μ μ -1 cm-2 in the higher concentration

region with a correlation coefficient of 0.9984 (from 0.05 to 10 mM).

The reason for two different sensitivities in the lower and higher

concentration regions may be the oxygen gas which developed during

the electrocatalytic decomposition of H2O2 by MnO2. The molecular

oxygen produced from the decomposition of hydrogen peroxide could

be adsorbed on the electrode surface and reduced according to the

mechanism shown above [28]. However, the adsorbed oxygen deters the

electron transfer such that the sensitivity is lower at a higher

concentration of H2O2 than at a lower concentration. Also, the limit of

detection of PANI-MnO2/GCE was calculated as 0.8 M (S/N=3). There μ

- 22 -

are several analysis parameters of various H2O2 sensors based on MnO2

in Table 1 for the comparison. It is shown that PANI-MnO2/GCE has

high sensitivity, a wide linear range, and a low limit of detection.

These results can be explained by the high surface area, good stability,

and improved electric conductivity at a neutral pH of PANI-MnO2

nanofibers.

- 23 -

Figure 8. (A) Amperometric response of PANI-MnO2/GCE on

successive injections of H2O2 into stirred N2-saturated 0.1 M PBS (pH

7.4) at -0.4 V. (B) The corresponding calibration curves of the current

response versus H2O2 concentration. Inset: calibration curve in the lower

concentration region (from 5 M to 50 M).μ μ

Elec

trod

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pplie

d po

tent

ial

(V)

Sens

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A m

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Line

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(M)

Lim

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de

tect

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(M

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Refe

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MnO

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mon

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CE

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107－

7.5×

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0.15

17

MnO

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P ag

greg

ates

/GC

E+0

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0.05

37.

8×10

7－

8.4×

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0.05

18

-MnO

β2

nano

rods

/GC

E+0

.80

21.7

42.

5×10

6－

4.3×

10–

2－

2.45

19

MnO

2NP-

CN

Fs/G

CE

+0.6

071

1.0×

105－

1.5×

10–

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1.1

20

MnO

2-DH

P/G

CE

+0.6

526

61.

2×10

7－

2.2×

10–

3－

0.08

21

MnO

2/CFM

E+0

.58

10.6

1.2×

105－

2.6×

10–

4－

5.4

22

MnO

2/VA

CN

Ts+0

.45

1080

1.2×

106－

1.8×

10–

3－

0.8

23

MnO

2/OM

C/G

CE

+0.4

580

6.8

5.0×

107－

6.0×

10–

4－

0.07

24

Ag-

MnO

2-MW

CN

T/G

CE

-0.3

082

.55.

0×10

7－

1.0×

10–

2－

1.7

25

MnO

2-GO

/GC

E-0

.30

38.2

5.0×

106－

6.0×

10–

4－

0.8

26

Au-

MnO

2-rG

O/G

CE

-0.2

098

010

1.6

1.0×

107－

2.2×

10–

5－

2.2×

105－

1.26

×10

–2－

0.05

27

PAN

I-MnO

2/GC

E-0

.40

403.

315

2.1

5.0×

10－

65.

0×10

–－

5

5.0×

10－

51.

0×10

–－

20.

8Th

is w

ork

T

able

1.

Elec

troan

alyt

ical

cha

ract

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tics

of v

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us m

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d hy

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en p

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ide

- 25 -

3.5. Selectivity, reproducibility, and stability

There are various electro-active chemical species, such as ascorbic

acid (AA), uric acid (UA), L-cysteine (L-Cys) and glucose, in

biological fluids. These can interfere with the electrochemical

determination of H2O2. Therefore, an interference study is needed for

biological applications of PANI-MnO2/GCE. Fig. 9 displays the

amperometric response of PANI-MnO2/GCE upon successive injections

of H2O2, AA, UA, L-Cys, and glucose (0.1 mM, respectively) in

N2-saurated 0.1 M PBS (pH 7.4) at an applied potential of -0.4 V. As

shown in Fig. 9, the observable amperometric response was only due to

the H2O2 reduction. Several MnO2-based electrochemical sensors were

significantly interfered with by ascorbic acid owing to the high positive

applied potential [17 20]. Hence, PANI-MnO– 2/GCE has an important

advantage when used as an electrochemical sensor for the selective

determination of H2O2.

We measured the current responses of five PANI-MnO2/GCE samples

in N2-saurated 0.1 M PBS (pH 7.4) containing 1 mM H2O2, finding

that the standard deviation of the responses was 3.1%. Furthermore, the

current responses of the electrodes remained at 97.6% after one week

of storage in ambient conditions. Therefore, the PANI-MnO2/GCE

showed good reproducibility and long-term stability.

- 26 -

Figure 9. Amperometric response of PANI-MnO2/GCE on successive

injections of H2O2, AA, UA, L-Cys, and glucose (each at 0.1 mM) in

N2-saurated 0.1 M PBS (pH 7.4) at 0.4 V.–

- 27 -

4. Conclusions

In this study, we fabricated a sensitive non-enzymatic electrochemical

sensor for H2O2 determination based on PANI-MnO2 nanofibers. The

sensor displayed good electrocatalytic activity toward H2O2 reduction in

PBS at pH 7.4. Moreover, it showed a wide linear range, a low

detection limit, high sensitivity, good reproducibility and good stability.

Particularly, the sensor showed excellent selectivity in ascorbic acid,

uric acid, L-cysteine and glucose due to its low applied potential.

Given their great performance, simplicity of fabrication, and low cost,

PANI-MnO2 nanofiber modified electrodes can be considered as

promising non-enzymatic sensors for real applications.

- 28 -

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- 33 -

μ μ

μ

μ