Electrochemical Sensor for Ascorbic Acid Based on

Graphene/CuPc/P ANI Nanocomposites

Saithip Pakapongpan!, Johannes Philipp Mensing!,2, Tanom Lomas! and Adisorn Tuantranont!

! Nanoelectronics and MEMs Laboratory National Electronics and Computer Technology Center

Pathumthani, Thailand 2 Faculty of Science, Mahidol University

Bangkok, Thailand sai thip. pakapongpan@nectec.or.th

Abstract- In this work, the electrochemical sensor based on

graphenel copper phthalocyanine(CuPc)1 polyaniline(PANI)

nanocomposite modified screen printed electrode(SPE) for

detection of ascorbicacid (AA) was successfully fabricated.

Copper phthalocyanine was immobilized on graphene by using

P ANI as a matrix. The nanocomposites were characterized by

electrochemical techniques such as cyclic voItametry. The sensor

exhibited a linear range from 100 11M to 3.6 mM (a correlation

coefficient of 0.9967). The sensitivity of the sensor was found to

be 22.92 rnA M-1 cm -2 and the limit of detection was 8.3 11M

(SIN = 3). Moreover, this sensor exhibited good electro catalytic

properties and lower the potential for the oxidation of ascorbic

acid which makes it a suitable sensor for detection of ascorbic

acid. The performance of this sensor could provide a promising

platform for the sensor or biosensor designs for AA detection.

Keywords- graphene; P ANI; copper phthalocyanine; ascorbic acid; electrochemical sensor

I. INTRODUCTION

Ascorbic acid (AA), also known as vitamin C, is a water soluble vitamin, widely present in many biological systems, fruits and vegetables. AA is commonly used to supplement inadequate dietary intake, as anti-oxidant and plays an important role in human metabolism as a free-radical scavenger, which may help to prevent radical induced diseases such as cancer and Parkinson's disease. Deficiency of AA will cause scurvy disease. It is administered in the treatment of many disorders, including Alzheimer's disease, atherosclerosis, cancer, infertility and in some clinical manifestations of HIV infections. Consequently, the determination of AA in various natural and prepared foods, drugs and physiological fluids, fruit juices, soft drinks, vegetables, etc. is very important for biological and agro-industry. Many methods have been previously reported to determination of AA, such as chemiluminescence, spectrometry, and luminescent methods. However, most of them have been based on its reducing properties. These methods lack specificity and are prone to interferences by other reducing agents in the sample [1]. Since AA is electroactive compound, electrochemical techniques for their detection have received considerable interest. Electrochemical method has been attention due to their high

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sensitivity, easy operation and low cost. The major problem for the electrochemical determination of AA is the interference from uric acid(UA). Overlapping oxidation of AA and UA has occurred because the oxidation potential they are very close at traditional electrodes. In addition, the oxidation product of UA can catalyze the oxidation of AA, which may lead to the electrode fouling with poor selectivity and reproducibility. Therefore, the selective detection of AA in the presence of UA is a major goal in this research field. For this purpose, various materials such as organic redox mediators, nanoparticles, polymers, self-assembled mono layers, and carbon nanotubes have been used in the modification of electrodes.

Metallophthalocyanines have been intensively studied since they exhibit many chemical and physical properties and electrodes modified with metalphthalocyanines have shown good electrocatalytic activity for many compounds [2].

Graphene, a flat monolayer of carbon atoms closely packed into a honeycomb two-dimensional lattice, has attracted tremendous attention from scientific communities in recent years. Due to its unique electronic properties arising from confinement of electrons in two dimensions, graphene has been considered as potential nanoscale building blocks for various applications such as field-effect transistors, gas sensors, and electromechanical resonators[3]. Polymer-modified electrodes have many advantages in the detection of analytes because of its high selectivity, sensitivity and homogeneity in electrochemical deposition, strong adherence to electrode surface and chemical stability of the film. P ANI is one of the most important conducting polymers due to its remarkable electrical, electrochemical and optical properties as well as good environmental stability. These above advantages make P ANI quite suitable as an electronic material, especially in the fabrication of sensors or biosensors[ 4].

In this paper, a novel sensor for determination of AA, the graphene/CuPc/P ANI nanocomposite was prepared by electrolytic exfoliation method. CuPc act as a catalyst for AA. The electrochemical properties and electrocatalytic activity of AA at modified electrode were characterized by cyclic voltammetry.

II. MATERIALS AND METHODS

A. Reagents and solutions

Graphite rods were purchased from Electron Microscopy Sciences (Hatfield, Pennsylvania). Ascorbic acid, Copper(II) phthalocyanine-tetrasulfonic acid tetrasodium salt and aniline were purchased from Sigma Aldrich. 0.1 M Phosphate buffer saline (PBS, pH 7.0) was prepared by mixing solution of Na2HP04 and NaH2P04. All solutions were prepared with deionized water.

B. Apparatus

All electrochemical experiments were performed with a computer controlled fl-Autolab modular electrochemical system (Eco Chemie Ultecht, The Netherlands). This instrument was operated using the GPES program (Eco Chemie) in a conventional three electrode electrochemical cell using screen printed electrode as working electrode, platinum wire as counter electrode and Ag/ AgCI saturated KCI as the reference electrode.

C. Preparation of graphenelCuPclP ANI composite material

modified electrode

Graphene/CuPc/P ANI has been prepared by the electrolytic exfoliation of graphite anodes in electrolyte containing CuPcTS. 5 mg/ml CuPcTS were dissolved in deionized water and electrolysis was performed with a constant potential of 17.5 V at room temperature for approximately 15 hours, followed by ultrasonication for 1 hour. The obtained suspension was then filtered with filter paper. Subsequently larger particles were removed by centrifugation at 5000 rpm for 30 and discarding of the sediment. Hydrochloric acid (37%) was added to the suspension to obtain an HCI concentration of 1 M. Now aniline was added to the acidic suspension until a concentration of 0.01 M is reached. The mixture was then ultrasonicated again for 30 minutes in order to facilitate J[-J[ bonding between graphene sheets and aniline molecules. To initiate the polymerization of P ANI the suspension was rapidly mixed with an equal volume of a 0.0025 M solution of ammonium persulfate (APS) in 1 M hydrochloric acid and left stirring overnight. After the polymerization the solid product is separated from the liquid by filtration with a 0.22flm pore diameter nitrocellulose membrane and washed with ethanol and DI water. Finally, the product was collected then dispersed in 200 fll of DI water.

The Graphene/CuPclP ANI modified electrode was fabricated by casting 5 fll of the solution on the surface of a screen printed electrode and followed by air drying for 8 hours.

III. RESULT AND DISCUSIONS

A. Electrochemical properties ofGraphene/CuPclP ANI modified electrode

Figure 1 shows cyclic voltamograms of different electrodes (a) bare SPE, (b) CuPc/PANI, (c) Graphene/CuPc/PANI in 0.1

M PBS pH 7.0 at 50 mV/s. No redox peak was observed at bare SPE and compare Graphene/CuPc/P ANI to the bare SPE can be seen that, a pair of redox peaks were clearly observed which indicated that CuPc immobilized on graphene and the backgroud current increases due to its high conductivity of graphene. The anodic and cathodic peak potential (Epa and Epc) were appeared at 0.16 V and 0 V, respectively. The peak-to­peak separation (LlEp) is 160 mY, indicating a fast electron transfer process, which demonstrated the successful immobilization of CuPc on the surface of graphene.

The effect of the scan rates was investigated. Figure 2 shows the cyclic voltamograms of the nanocomposited with different scan rates from 10 to 100 mV/s. The resulting suggested that the electrode reaction was diffusion controlled processes.

8.0x10·5 � _____ ------------, --BareSPE -- Graphene/CuPc/PANI -- CuPc/PANI

4.0x10·5

« 0.0

-4.0x10·5

-8.0x1 0.5 .J....."T"""�--r---r--�---,.---�--,----1 -0.6 -0.3 0.0

E/V

0.3 0.6 0.9

Figure 1 Cyclic voltammograms of (a) bare SPE, (b) CuPc/P ANI, ( c) Graphene/CuPc/P ANI modified SPE at a scan rate of 100 mY/so

« 0

_3x10·5

-0.6 -0.3 0.0 0.3

E/V

0.6

Figure 2 Cyclic voltammograms of Graphene/CuPc/P ANI modified SPE at various scan rates (from inner to outer): 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 mV/s.

B. Electrochemical catalytic toward AA of the modified

elctrode

The determination of AA concentration was performed using cyclic voltammetry method. Figure 3 shows the curves of the different AA concentrations on the Graphene/CuPc/P ANI modified electrode. The electrocatalytic properties of nanocomposites towards AA, cyclic voltammograms obtained using a modified with and without injection of AA. In absence of AA( first curve), the oxidation and reduction peak current did not change. After injection of AA the result shows that the oxidation peak current increased with increasing AA concentration from 100 IlM to 3.6 mM and the reduction peak current was decreased. It indicated that the Graphene/CuPc IP ANI modified electrode shows good electrochemical catalytic toward AA.

1.5x10·4 ,------------------,

1.0x10·4

5.0x10·5

0.0

-0.3 0.0 0.3 0.6

E/V

Figure 3 Cyclic voltamogram of Graphene/CuPc/P ANI modified electrode in the presence 100 IlM to 3.6 mM of AA concentrations in 0.1 M PBS pH 7.0 at a scan rate of 50 mV Is.

75 �-----------------------------,

60

45

30

15

o

o 2 3 4

AA concentration I mM

Figure 4 Calibration curve of the AA concentration vs current response.

C. Calibration

The calibration curve of the current response of the sensor was shown in Figure 4. The measured peak current was proportional to the AA concentration in the range of 100 IlM to 3.6 mM . The linear response range of the sensor spans from 100 IlM to 2.4 mM with the linear equation is obtained y = 22.921x + l.7248 (r2=0.9967) and a detection limit of 8.3 IlM (S/N=3).

IV. CONCLUSION

We have successfully prepared Graphene/CuPc/P ANI nanocomposites modified SPE and used to investigate the electrochemical catalytic of AA. The nanocomposited showed high selectivity, wide range and electrocatalytic activity towards AA. The performance of the Graphene/CuPc/P ANI was evaluated by CV. The results indicate that the graphene and P ANI can promote the electron transfer of AA at the electrode, improve the conductivity and surface volume by graphene. This sensor introduced a selective for AA, which great promise for sensor or biosensor application in the clinical diagnosis, pharmatical analysis and in the field of bio­electrochemistry.

ACKNOWLEDGMENT

This work was supported financially by National Science and Technology Development Agency (NSTDA).

REFERENCES

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[2] X. Zuo, H. Zhang, N. Li, "An electrochemical biosensor for determination of ascorbicacid by cobalt (IT) phthalocyanine-multi­walled carbon nanotubes modified glassy carbon electrode" Sensors and Actuators B: Chemical, vol. 161,2012, pp. 1074-1079.

[3] K. Zhou, Y. Zhu, X. Yang, J. Luoa, C. Li, S. Luan, "A novel hydrogen peroxide biosensor based on Au-graphene-HRP-chitosan biocomposites". Electrochimica Acta, vol. 55, 2010, pp. 3055-3060.

[4] E. Coskun, E.A. Zaragoza-Contreras, H.J. Salavagione, "Synthesis of sulfonated graphene/polyaniline composites with improved electroactivity". Carbon, vol. 50,2012, pp. 2235-2243.