High loading Pt nanoparticles on functionalization of carbon nanotubes for fabricating nonenzyme hydrogen peroxide sensor

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High loading Pt nanoparticles on functionalization of carbon nanotubes for fabricating nonenzyme hydrogen peroxide sensor Xiaoyan Li, Xiuhui Liu, Weiwei Wang, Lin Li, Xiaoquan Lu

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S0956-5663(14)00227-9 http://dx.doi.org/10.1016/j.bios.2014.03.046 BIOS6674

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Biosensors and Bioelectronics

Received date: 21 December 2013 Revised date: 9 March 2014 Accepted date: 24 March 2014 Cite this article as: Xiaoyan Li, Xiuhui Liu, Weiwei Wang, Lin Li, Xiaoquan Lu, High loading Pt nanoparticles on functionalization of carbon nanotubes for fabricating nonenzyme hydrogen peroxide sensor, Biosensors and Bioelectronics, http://dx.doi.org/10.1016/j.bios.2014.03.046 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

High loading Pt nanoparticles on functionalization of carbon nanotubes for fabricating nonenzyme hydrogen peroxide sensor Xiaoyan Li, Xiuhui Liu , Weiwei Wang, Lin Li, Xiaoquan Lu Key Laboratory of Bioelectrochemistry & Environmental Analysis of Gansu Province, College of Chemistry & Chemical Engineering, Northwest Normal University, Lanzhou, 730070, China

Abstract A

very

efficient,

simple

approach

was

developed

to

fabricate

a

high Pt nanoparticles-loading multiwall carbon nanotube (MWCNTs) amperometric sensor for hydrogen peroxide (H2O2) determination. In this strategy, MWCNTs was first functionalized with an anionic surfactant, sodium dodecyl sulfate (SDS); then the Pt nanoparticles (NPs) were loaded on MWCNTs-SDS by electrodepositing. The large amounts of Pt nanoparticles could be well deposited on the surface of the MWCNTs-SDS modified electrode, as revealed by scanning electron microscopy (SEM). In addition, the PtNPs/MWCNTs-SDS composite was also characterized by electrochemical methods including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The experimental results demonstrated that the constructed electrode exhibited good catalytic activity toward the hydrogen peroxide, and obtained a wide linear range from 5.8 × 10-9 to 1.1 × 10-3 M with a limit of detection (LOD) of 1.9 × 10-9 M, which was superior to that obtained with other H2O2 electrochemical sensors reported previously. Moreover, it can also be applied to real samples analysis. The excellent performance of hydrogen peroxide sensor was ascribed to the MWCNTs-SDS composites being used as effective load matrix for the

Correspondingauthor.Tel.:+8609317975276;fax:+8609317971323.Email:[email protected]

Correspondingauthor.Tel.:+8609317971276;fax:+8609317971323.Email:[email protected]

 1

deposition of PtNPs and the synergistic amplification effect of the two kinds of nanomaterials—PtNPs and MWCNTs.

Keywords:

Functionalized

carbon

nanotubes;

sodium

dodecyl sulfate;

Pt

nanoparticles; hydrogen peroxide; amperometric sensor.

1.

Introduction An accurate and reliable method for the determination of hydrogen peroxide (H2O2)

is of interest to many fields but particularly in biosensing because H2O2 is a reactive oxygen species (ROS) and a by-product of the reactions catalyzed by a large number of oxidase enzymes. Moreover, in living organisms, H2O2 also plays an essential role as a signalling molecule in regulating diverse biological processes.(Giorgio et al., 2007; Geiszt and Leto, 2004; Chen et al., 2012) Among various detection techniques for H2O2 (such as titrimetry (Hurdis and Romeyn, 1954), spectrophotometry (Matsubara et al., 1992) and chemiluminescence (Hanaoka et al., 2001)), electrochemical method has attracted considerable interest due to its high sensitivity, fast response, low-cost and convenient operation.(Lin et al., 2010) Recently, numerous

enzymes

modified

electrodes,

especially

horseradish

peroxidase

(HRP)-based electrodes, are frequently used for detecting relatively low concentrations of H2O2. (Kong et al., 2003; Xiang et al., 2009; Yin et al., 2009; Liu et al., 2013 ) However, the relatively of high cost, limited lifetime and the critical operating situationlimit enzyme-biosensors applicability. Therefore, the development of nonenzymatic sensors with low detection limit has drawn more attention recently. (Yuan et al., 2008; Zhang et al., 2009; Bui et al., 2010 ) Nowadays, with the development of nanotechnology, nanomaterials, especially metal nanoparticles(NPs), play an important role in improving sensor performance. During these years, PtNPs have been used as enzyme mimics to catalyze the H2O2 (Bo et al., 2010; Bian et al., 2010᧷Fang et al., 2012; Liu et al., 2011), since the over-potential occurred at unmodified electrodes was decreased a lot. (Lin et al., 2

2010; Chu et al., 2007) Recent studies found that performance of the H2O2 sensor depended strongly on the size, shape and distribution of PtNPs on the electrode. (Peng and Yang, 2009; Chen et al., 2007 ) Therefore, the matrix for the preparation of highly dispersed PtNPs is very important. Carbon nanotubes (CNTs), as another typical nanomaterial, have aroused growing interest in nonenzymatic sensors since they possess relatively large surface area, high chemical stability, strong adsorptive ability, excellent electric conductivity, and outstanding ability to promote electron-transfer reactions. (Nie et al., 2011) In order to take full advantage of the two kinds of nanomaterials, nanocomposites have been widely used in preparing biosensors. (Fang et al., 2012; Zhao et al., 2009; Li et al., 2013) For example, Hrapovic et al. fabricated an electrochemical H2O2 sensors based on platinum nanoparticles and SWCNTs, which yielded good performance toward the detection of H2O2. (Hrapovic et al., 2003) Nevertheless, disaggregation and uniform dispersion of CNTs are critical challenges that must be met to successfully produce such high property materials.(Vaisman et al., 2006) Fortunately, a simple and nondestructive method for improving nanotube solubilization was developed based on noncovalent interactions of sodium dodecyl sulfate (SDS) with nanotube surfaces. (Zhang and Gao, 2007; Lin et al., 2010; Li et al., 2012) The SDS molecules were adsorbed on the surface of CNTs with the formation of hemi micelles, which made each individual carbon nanotubes suspended well in solution and prevented them from the aggregation into bundles and ropes.(Richard et al., 2003; Islam et al., 2004) In addition, the adsorbed SDS molecules on the surface of CNTs, resulting in enhanced hydrophilic nature of the CNTs, could act as anchoring sites for metal nanoparticles. (Fang et al., 2011) Thus, these results showed that SDS-functionalized CNTs is expected to create more opportunity for applications in sensors. The aim in this article is to fabricate a novel nonenzymatic sensor of H2O2 by utilizing SDS-functionalized MWCNTs as the matrix for electrodepositing of PtNPs. By combining the advantages of MWCNTs and PtNPs, the sensor exhibits excellent performance towards H2O2 with low detection limit, wide linear range, excellent selectivity and reproducibility, and can be applied to real samples analysis. Besides, 3

the sensor’s properties were also investigated detailed.

2. Experimental Section 2.1 Apparatus The surface morphology of PtNPs/MWCNTs-SDS composite was characterized by JSM-6701F scanning electron microscopy (SEM, Japan). FT-IR spectra of KBr powder-pressed pellets were recorded on a Fourier Transform-Infrared (FT-IR) spectrophotometer (USA). Electrochemical measurements were performed on a CHI660C electrochemical workstation (Austin, TX, USA) with conventional three-electrode system. A bare or modified glassy carbon electrode (GCE, d = 3.0 mm) was employed as working electrode. A platinum electrode and a saturated calomel electrode (SCE) were served as the auxiliary and reference electrode. All potentials given in this paper were referred to the SCE. Electrochemical impedance spectroscopy (EIS) experiments were performed on Multi-potentiostat (VMP2, Princeton Applied Research, USA). Before each electrochemical measurement, solutions were thoroughly deoxygenated by bubbling nitrogen through the solution for at least 20 minutes to remove dissolved oxygen.

2.2 Reagents The multi-walled carbon nanotubes (MWCNTs) used (diameter: 20– 40 nm, length: 1–2 m, purity: 95%) came from Shenzhen Nanotech Port Co. Ltd. (Shenzhen, China). Before use, MWCNTs were purified according to the reported literature with slight modification. (Liu et al., 2013) Hydrogen peroxide solution (30 wt%) was purchased from Beijing Chemical Reagent (Beijing, China), hexachloroplatinic acid (H2PtCl6·6H2O) was purchased from Aladdin, sodium dodecyl sulfate (SDS᧨C12H25SO4Na) from Tianjin Chemical Reagent (Tianjin, China), Na2SO4 was bought from Shanghai Chemical Reagent (Shanghai, China). PBS (pH 7.0) was prepared by mixing suitable amounts of 0.2M NaH2PO4/Na2HPO4. All chemicals were of analytical grade and solutions were prepared with deionized water.

4

2.3 MWCNTs functionalization SDS functionalized MWCNTs (MWCNTs–SDS) was prepared by previously reported method (Li et al., 2012). In general, 0.1g of MWCNTs were suspended in 400 mL of 0.25 M sodium dodecyl sulfate(SDS) aqueous solution, and then was ultrasonicated for 1 h and stirred for 24 h. After that, MWCNTs–SDS was filtered by nylon membrane with 0.22 <m> pores, thoroughly washed with water to remove the free SDS in the solution, followed by drying in a vacuum oven at 60 C for 24h. So, SDS functionalized MWCNTs were obtained. The structure and composition of the MWCNTs-SDS have been verified by FT-IR.

2.4 Preparation of the H2O2 sensor A GC electrode was polished with 1.0, 0.3 and 0.05˩m alumina slurry to a mirror-like, respectively, followed by rinsing thoroughly with doubly distilled water. Then 10 L of MWCNTs–SDS aqueous solution (0.2mg/mL) was dropped on the surface of a GCE and dried in air, and then the MWCNTs-SDS/GCE was obtained. Next, the electrode was electrodeposited in the solution containing 1.0 mM H2PtCl6 and 0.2 M Na2SO4 for 200s at -0.2V to obtain Pt NPs/MWCNTs-SDS modified electrode.

3. Results and discussion 3.1. Characterization of MWCNTs-SDS 3.1.1. FT-IR characterization of MWCNTs-SDS In order to understand the nature of surface modification of MWCNTs by SDS micelles, the FT-IR transmittance patterns of MWCNTs-SDS (Fig.S1 a) along with SDS samples (Fig.S1 b) and MWCNTs (Fig.S1 c) were shown in Fig. S1. We can see that MWCNTs showed a flat transmittance profile between 2000 and 3000cm1. However, the FT-IR spectrum of MWCNTs-SDS was very similar to that of pure SDS, showing strong bands of asymmetric and symmetric stretching of –CH2– at 2920 and 2854 cm1, respectively (Jiang et al., 2003; Lin et al., 2010), indicating adsorbed surfactant molecules on the MWCNTs surface. 5

3.1.2. Electrochemical characterization of MWCNTs-SDS Cyclic voltammetry (CV) was utilized to monitor the electrochemical behaviors of different electrodes in the solution containing 5.0 mM [Fe(CN)6]3-/4- and 0.1 M KCl as shown in Fig.S2(A). One-electron redox behavior of ferricyanide was observed on the GC electrode (Fig. S2(A) curve a). After modified with MWCNTs, the anodic peak and cathodic peak increased in Fig. S2A curve c, indicating MWCNTs could improve the active surface area of the electrode. While the MWCNTs-SDS modified electrode was scanned in the same solution, the peak current (curve b) decreased a lots compared with the MWCNTs/GCE (curve c). The reason, we think, may be ascribed to the adsorption of the SDS molecules onto the MWCNTs᧨resulting a distribution of negative charges at the tube surfaces, which hindered the diffusion of [Fe(CN)6]3-/4toward the electrode surface owing to the electrostatic repulsion. In order to further confirm above speculation, a comparative study was carried out by using Ru(NH3)63+ as the electrochemical probe, and the typical cyclic voltammograms of different electrodes were shown in Fig.S2(B). A pair of peaks was also observed in each CV, which was ascribed to the redox of Ru(NH3)63+. Different from Fig.S2(A), the highest peak among the three curves was curve b, confirming that the absorbed SDS could improve the diffusion of Ru(NH3)63+ toward the electrode surface owing to the electrostatic attraction.

3.2. Characterization of PtNPs/MWCNTs-SDS/GC electrode 3.2.1. Surface morphology of the sensor Scanning electron microscopy (SEM) was used to characterize and compare the morphologies of MWCNTs-SDS and PtNPs/MWCNTs-SDS. From Fig. 1A, one can see that the MWCNTs-SDS composite formed the network-like structure, suggesting that the SDS used here could serve as good disperser for MWCNTs. The tails of the SDS molecules enable attachment to the inert surface of MWCNTs and the hydrophilic heads with negative charge enable separation/dispersion of MWCNTs into 6

individual tubes.(Lin et al., 2010) After Pt electrodeposited on MWCNTs-SDS composite, it is clearly that small-sized PtNPs (dots in Fig. 1B, roughly spherical in shape with an average diameter of about 50 nm) presented at moderately high density, non-ordered distribution along the walls of nanotubes. In contrast, in the absence of MWCNTs-SDS, PtNPs had rather large mean size (about 100 nm) with low density, and their distribution was also nonuniform as shown in Fig.1C.

3.2.2. Electrochemical behaviors of PtNPs/MWCNTs-SDS/GC electrode Cyclic Voltammetry (CV) is a common and convenient method to characterize the catalytic activities of the as-synthesized electrodes. Figure 2 presents cyclic voltammograms (CVs) of various modified electrodes in N2-saturated 0.2M PBS (pH 7.0), respectively. Compared with bare GCE (curve a) and MWCNTs-SDS/GCE (curve b), one can see that a cathodic peak at 0.091V was obtained on the PtNPs/GCE (curve c) and PtNPs/MWCNTs-SDS/GCE (curve d), respectively, which was attributed to the reduction of platinum oxide, proving the existence of PtNPs on the bare GCE and modified electrode, respectively. It is noticeable that the peak current of curve d is much higher than that of curve c, illustrating great amount of PtNPs loaded on MWCNTs-SDS/GCE. Therefore, MWCNTs-SDS composite film is fit for the effective load matrix for the deposition of PtNPs on GCE. Moreover, two pairs of hydrogen adsorption/desorption peaks in the potential range of -200 to -600 mV were clearly discerned in curves c and d, suggesting the availability of a clean Pt surface for electrocatalyzing the hydrogen-involved reactions. (Zhao et al., 2007) On the other hand, electrochemical impedance spectroscopy (EIS) is also an effective method for probing the features of surface modified electrodes. A typical impedance spectrum includes

a semicircle portion

at higher frequencies

corresponding to the electron transfer-limited process and a linear part at lower frequency range representing the diffusion limited process. The semicircle diameter corresponds to the electron-transfer resistance (Ret), which can be used to describe the interface properties of the electrode. By using [Fe(CN)6]3-/4- as the electrochemical probe, the Nyquist plots of different electrodes were shown in Fig.3 and the inset is 7

the fits of equivalent circuit. The impedance spectra of the bare GCE (Fig. 3a) consisted of a small semicircle (Ret: 100) with an almost straight tail line, which was the characteristic of a diffusion limiting step of the electrochemical process. However, the estimated electron transfer resistance for MWCNTs-SDS/GCE (b) and PtNPs/MWCNTs-SDS/GCE (c) were 48 and 32, respectively. This result indicated that the higher electron conduction pathways were formed on the MWCNTs-SDS and PtNPs/MWCNTs-SDS between the electrode and electrolyte. (Liu et al., 2005; Zou et al., 2008). This was agreed with the result from cyclic voltammetry. Furthermore, the Ret of PtNPs/MWCNTs -SDS-modified GC electrode is the lowest among the three electrodes because Pt nanoparticles play an important role in increasing the electroactive surface area and the synergistic action of the electrocatalytic activity of PtNPs and CNTs.

3.3. Electrochemical response of H2O2 at the PtNPs/MWCNTs-SDS/GCE The comparison investigations of the electrochemical response of H2O2 at different electrodes were demonstrated in Figure 4. For bare GCE (curve a) and MWCNTs-SDS/GCE (curve b), nearly no redox activity is observed for H2O2, illustrating that the redox of H2O2 was hardly achieved at such electrodes due to slow electrode kinetics and high overpotential. (Chen et al., 2012) In contrast, Pt nanoparticles modified electrodes exhibit excellent response signals with the much higher catalytic current and lower over-potential (0.091 V) as shown in curves c-e. This observation is a clear evidence of electrocatalysis of PtNPs, proving that the detection of H2O2 was favored on oxidized Pt surfaces.( Lingane, 1961; Hall et al., 1997) In addition, the peak current (Ipc) of PtNPs/MWCNTs-SDS/GCE (curve e) is 1.6 times and 1.3 times as large as that of PtNPs/GCE (curve c) and PtNPs /MWCNTs/GCE (curve d), respectively, suggesting that PtNPs/MWCNTs-SDS/GCE possesses good catalytic ability to H2O2. The good catalysis property of PtNPs/MWCNTs-SDS/GCE to H2O2 may result from the following three factors. Firstly, as well known, the catalytic property of Pt is size-dependent, and the small-sized Pt nanoparticles will lead to higher catalytic 8

ability for H2O2 because they could provide large active area to contact H2O2 for the electrocatalytic process. Secondly, the presence of MWCNTs-SDS also plays a significant role in the good performance of the modified electrode. The adsorbed SDS molecules on the surface of MWCNTs acted as anchoring sites for Pt nanoparticles electrodeposition, preventing them from aggregation. Moreover, the network-like structure of MWCNTs-SDS composite used here as a supporting matrix could disperse PtNPs well and load on great amount of PtNPs, which could be found in Fig. 1. Finally, MWCNTs-SDS effectively enhanced the conductivity of the modified electrode, and facilitated the electron transfer. In addition, a comparative study was carried out by calculating surface coverage (*) of the three kinds of electrodes: (a) PtNPs/MWCNTs-SDS/GCE, (b) PtNPs/MWCNTs/GCE, (c) PtNPs/GCE. Firstly, the CVs were performed in the presence of redox probe Fe(CN)63/4 at a series of scan rates, respectively, on the electrodes as shown in Fig. S3. The average electroactive surface areas could be calculated according to the Randles–Sevcik equation (Zeng et al., 2007) : Ip=2.69×105×A×D1/2×n3/2×v1/2×c

(1)

where Ip relates to the redox peak current, A is the area of the electrode (cm2), the diffusion coefficient (D) of the molecule in solution is (6.70 ± 0.02) × 106 cm2/s, n represents the transferring electron number, c corresponds to the bulk concentration of the redox probe (mol/cm3 ) and v is the scan rate (V/s). Ip (as well as the current at any other point on the wave) was proportional to vl/2. According to the above equation, we can get the approximate value of A. Then the surface coverage (*) of electroactive PtNPs can be estimated from the equation Q = nFA* (Q is quantity of electric charge(C)). The results from coulometric analysis of Pt reduction peak were shown in Table S1. The surface coverage of the PtNPs depositing on the MWCNTs-SDS/GCE (4.57×10-10mol/cm2) was 1.3 times as large as that of on the MWCNTs/GCE ( 3.56×10-10mol/cm2) , which further prove that the MWCNTs could be considerably untangled with the modified SDS, so as to greatly increase the effective area of the electrode to load more PtNPs. 9

3.4. Performance of the hydrogen peroxide sensor 3.4.1. Optimization of experimental variables In order to obtain an efficient sensor for detection H2O2, the analytical conditions, such as the MWCNTs-SDS concentration, PtNPs electrodeposition time, PtNPs electrodeposition potential and H2PtCl6 concentration, were optimized by the prepared hydrogen peroxide sensor as shown in Fig.S4. The experiment results showed that the PtNPs/MWCNTs-SDS/GCE has the best response current for H2O2 at the following conditions: 10L MWCNTs-SDS (0.2mg/mL), 1.0mM H2PtCl6 concentration, 200s electrodeposition time, and -0.2V electrodeposition potential.

3.4.2. Amperometric response and calibration curve The amperometric responses of PtNPs/MWCNTs-SDS/GCE with the successive additions of H2O2 to N2-saturated 0.2M PBS (pH 7.0) at an applied potential -0.1V, were shown in Fig. 5. The current responses of the sensor increased along with H2O2 concentrations. The response to logarithm of the H2O2 concentration (inset of Fig. 5B) showed linear range from 5.8 × 10-9 to 5.0 × 10-6 mol/L , and the linear regression equation was Ip(A)=0.4493lg[H2O2]+4.0968 with a correlation coefficient of 0.9946. Another linear relationship could be established between the peak current and the concentration of H2O2 in the range from 1.3 × 10-5 to 1.1×10-3mol/L (Fig. 5D), and the linear regression equation was Ip(A)=0.0058[H2O2](M)+1.6421 with a correlation coefficient of 0.9997. The detection limit of as-prepared electrochemical sensor was 1.9 × 10-9 mol/L, at the ratio of signal to noise of 3. Table S2 summarizes this sensor performance based on PtNPs/MWCNTs-SDS composite and other relevant sensor materials collected from literatures. We found that the performance of the proposed sensor was better than other nonenzyme H2O2 sensors or comparable to some enzyme-biosensors (Liu et al., 2013; Wang et al., 2009).

The

result

indicated

that

the

high

electrocatalytic

efficiency

of

PtNPs/MWCNTs-SDS sensor is attributed to the large quantities of Pt nanoparticles, which were well dispersed on the MWCNTs-SDS surface. 10

3.4.3. Selectivity, reproducibility and stability of the H2O2 sensor The influence of common interfering substances such as ascorbic acid (AA), uric acid (UA) was studied. 0.5mM AA and 0.5mM UA were added in 10M H2O2, and the current responses of the sensor were shown in Fig.S5 (Column B, C, D). Compared to H2O2, the interfering species yielded current response ranging from 0.33% (AA) to 1.2% (UA), indicating that the PtNPs/MWCNTs-SDS/GCE could be used for the selective and sensitive detection of H2O2. The reproducibility was estimated from the response to 0.5M H2O2 at five different H2O2 electrodes in Fig.S6, and an acceptable RSD of 2.27% was acquired. Moreover, it could retain 91% of the original value after 50 consecutive measurements as shown in Fig.S7.

3.4.4. Real sample analysis The feasibility of the device for practical applications was carried out by analyzing the 1% human serum. The concentration of hydrogen peroxide in serum samples was determined to be 17.03±0.02 nM (n=3) by chronamperometry measurement, and the recoveries of hydrogen peroxide samples with concentrations of 10nM (sample 2) 20nM (sample 3) and 30nM (sample 4) were obtained in Table 1. These results were consistent with our previously reported. (Li et al., 2013), and showed that the sensor has a potential in detection of hydrogen peroxide directly in biological samples.

4. Conclusion By combining the advantages of MWCNTs and PtNPs, the fabricated sensor in this paper significantly improve the amperometric detection of hydrogen peroxide. This work indicate that the sensor has the potential application in many different fields, ranging from the very low levels of hydrogen peroxide produced in biological systems to the millimolar levels found in some industrial processes.

Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 11

21245004, 20875077)

Supporting Information: Characterization of MWCNTs-SDS, the study of the average electroactive surface areas of modified electrode, optimization of experimental variables, and the study of selectivity, reproducibility and stability of the modified electrode.

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Fig.1. SEM images of differently modified GC substrates: (A) MWCNTs-SDS/GCE; (B) PtNPs/MWCNTs-SDS/GCE; (C) PtNPs/GCE. Fig.2. Cyclic voltammograms of bare GCE (a) and MWCNTs-SDS/GCE (b) PtNPs/GCE (c) and PtNPs/MWCNTs-SDS/GCE (d) in the solution of N2-saturated 0.2 M PBS (pH 7.0) , at 50 mV/s. Fig.3. EIS of (a) bare GCE, (b) MWCNTs-SDS/GCE, (c) PtNPs/MWCNTs -SDS/GCE in 5.0 mM [Fe(CN)6]3-/4- and 0.1M KCl. Fig.4. CVs of different electrodes in 2.0mM H2O2 and N2-saturated 0.2M PBS (pH 7.0):(a)bare GCE, (b)MWCNT-SDS/GCE, (c) PtNPs/GCE, (d) PtNPs/MWCNTs/GCE and (e) PtNPs/MWCNTs–SDS/GCE, at 50 mV/s. Fig.5.(A) The chronoamperometry current–time curve of PtNPs/MWCNTs-SDS/GCE in N2- saturated 0.2M PBS (pH 7.0) containing various concentrations of H2O2 (from a to j: 0 , 5.8 × 10-9 ,1.2 × 10-8 , 2.3× 10-8 , 5.8 × 10-8 , 2.2 × 10-7 , 5.1 × 10-7 , 1.3 × 10-6 , 2.4 × 10-6 and 5 ×10-6 M), at -0.1V; (B) The calibration curve between current and lg[H2O2].(C)The chronoamperometry current–time curve of PtNPs/MWCNTs-SDS /GCE with successive addition of (from k to q: 1.3 × 10-5 ,2.5 × 10-5, 5.7× 10-5 , 1.1 × 10-4 , 2.2 × 10-4 , 5.1 × 10-4 , 1.1 × 10-3 M) to N2- saturated 0.2M PBS (pH 7.0) at -0.1V. (D) The calibration plots illustrating the linear electrode response to H2O2 addition.

14

Table.1 Determination of H2O2 in human serum samples. Sample

Added (nM)

Found (nM)

Recovery (%)

1

0

17.03

2

10

9.01

90.1%

3

20

19.97

99.8%

4

30

30.77

102.6%

Highlights z

A

novel

nonenzymatic

H2O2 sensor

was

constructed

based

on

PtNPs/MWCNTs-SDS modified GCE. z

SDS functionalized carbon nanotube was used as matrices for deposition of PtNPs effectively.

z

High loading and small-sized PtNPs were formed on the MWCNTs-SDS film.

z

PtNPs/MWCNTs-SDS/GCE displayed excellent electrocatalytic activity to H2O2 and applied to real samples.

z

A significant low detection limit of 1.9nM with wide linear range from 5.8 × 10-9 to 1.1 × 10-3 M was achieved at this sensor.

15

Figure1

Figure 2

Figure 3

Figure 4

Figure 5