1. A Study of Carbon Paste Electrode Modified with Platinum Particles and Ferrocene and Its Application to Glucose Biosensor Yi-Sheng Wang ( 汪乙生 ), Ting-Li Lin ( 林庭立 ), Hau Lin ( 林浩 ) Department of Chemical and Materials Engineering, Southern Taiwan University 南台科技大學化學工程與材料工程系 ABSTRACT A study was conducted to use the platinum particles and ferrocene to modify the carbon paste electrode which was used as the working electrode to detect the responding current of reduction of hydrogen peroxide and then the concentration of hydrogen peroxide could be obtained from the responding current and consequently, the concentration of the glucose could be determined. The results showed that the responding current for the carbon paste electrode modified with ferrocene was elevated significantly. The optimum weight ratio for ferrocene : graphite carbon powders was 3 : 7. At 30 ℃, -0.2 V operating potential, and in 0.05 M PBS phosphate buffer solution (PBS), the TB (Time Base) graphs for the carbon paste electrode modified with different ratios (0%, 1%, 3%, 5%, and 7%) of platinum particles were plotted to evaluate the effect of platinum particles on the responding current of detection of hydrogen peroxide. At 30 ℃, -0.2V operating potential, and in 0.05 M phosphate buffer solution ( pH = 7.4 ), when the carbon paste electrode was modified with ferrocene [ferrocene : graphite carbon powders = 3 : 7 ( weight ratio )], the detection limit was 0.06 mM C 6 H 12 O 6 ; the linear range was 0.06 ~ 2.0 mM C 6 H 12 O 6 ; R 2 = 0.992 and the sensitivity was 83.1 μA/ cm 2 ． mM C 6 H 12 O 6. INTRODUCTION Nowadays, diabetes is one of the top ten causes of death for the people in Taiwan. Therefore, developing a rapid, convenient, and economical glucose biosensor for detecting the glucose is a very important research subject. The glucose and oxygen can be catalyzed by the glucose oxidase and the glucose is oxidized to gluconic acid and the oxygen is reduced to hydrogen peroxide. Because the ferrocene (Fe(C 5 H 5 ) 2 ) possesses the excellent conductivity and catalytic characteristic, it can be used to elevate the responding current for detection of reduction of hydrogen peroxide. A study was conducted to use the platinum particles and ferrocene to modify the carbon paste electrode which was used as the working electrodes to detect the responding current of reduction of hydrogen peroxide in the phosphate buffer solution(PBS) and then the concentration of hydrogen peroxide could be obtained from the responding current and consequently, the concentration of the glucose could be determined. EXPERIMENTAL SECTION Equipment Electrochemical Analyzer (BAS 100W) was used to measure the activity of electrode by Cyclic Voltammetry ( CV ) and Time Base ( TB ) mode ; pH meter (Metrohm 731); Constant Temperature Thermal Bath (Wisdom BC-2DT 10L); Oven (DENG YNG) ; Electric Stirrer (Fargo); Carbon Paste Electrode was used as the working electrodes, Coiled Platinum Wire was used as the counter electrode and Ag / AgCl was used as the reference electrode. Chemicals and Reagents Ferrocene(Fe(C 5 H 5 ) 2 ); Hydrogen Peroxide (H 2 O 2 ); D(+)-Glucose Monohydrate(C 6 H 12 O 6 ); Glucose Oxidase(EC 1.1.3.4, Type X-S: From Aspergillus Niger, 50000 units/mg); Graphite Carbon Powder; Carbon Paste; Cyclohexanone(C 6 H 10 O); Nafion ; Potassium Dihydrogenphosphate (KH 2 PO 4 ); Potassium Chloride (KCl). Procedure (1) Take one section of 7 cm electric wire with 0.05 cm inside diameter. After depriving the coating 0.5 cm length from both ends, the nake-ended wire was washed, dried and ready for use. 7 cm 0.5 mm 0.5 cm (2) Then the ferrocene powders, graphite carbon powders and carbon paste were mixed with the appropriate ratio (ferrocene : graphite carbon powders : carbon paste = 0.3 : 0.7 : 1). After the mixing was complete, the mixture was evenly coated on the nake- ended electric wire and dried in the oven and then we obtained the carbon paste electrode. The surface area of the carbon paste electrode was 0.0805 cm 2. Ferrocene Mixing with carbon paste Graphite carbon powders Coated on the nake- ended electric wire glucose oxidase1 % Nafion PVC cover (3) After the above mentioned carbon paste electrode was dried, the 2μL glucose oxidase solution( 3mg of glucose oxidase was dissolved in 500μL PBS buffer solution ) was put onto the surface of electrode and the electrode was dried at room temperature. Then 5μL of 1% Nafion solution(in 95% alcohol) was dropped onto the electrode evenly and after the electrode was dried at room temperature, we obtained the glucose biosensor. RESULTS AND DISCUSSION Fig 1. CV graphs for (A) carbon paste electrode modified with ferrocene (B) unmodified carbon paste electrode; the range of scanning potential: -0.8 ～ +0.8 V, scanning rate = 50 mV/s Fig. 3 The platinum particles observed by TEM (Transmission Electron Microscope) Fig. 4 The TB graphs of carbon paste electrodes for detection of H 2 O 2 at different ratios of platinum particles; the ratios of platinum particles are [ (A) 0% (B) 1% (C) 3% (D) 5% (E) 7% ], 10 μL of 50mM H 2 O 2 is injected per 100 seconds Fig.5 The TB graph of glucose biosensor for detection of glucose (ferrocene : graphite carbon powders = 3 : 7); At 30 ℃ ; the operating potential = –0.2 V; in 0.1 M KCl of 5 mL 0.05 M PBS buffer solution ( pH=7.4 ); stirring rate =500 rpm; 3μL, 6μL, 12μL, and 20μL of 100mM glucose are injected at 100 seconds, 200 seconds, 300 seconds, and 400 seconds respectively Fig. 6 The TB graph of glucose biosensor for detection of glucose (ferrocene : graphite carbon powders = 3 : 7); At 30 ℃ ; the operating potential = –0.2 V; in 0.1 M KCl of 5 mL 0.05 M PBS buffer solution ( pH=7.4 ); stirring rate=500 rpm; 20μL of 100mM glucose is injected per 100 seconds CONCLUSIONS The results showed that the responding current for the carbon paste electrode modified with the ferrocene was elevated significantly. The optimum weight ratio for ferrocene : graphite carbon powders was 3 : 7. When the carbon paste electrode was modified with 7% of platinum particles, the responding current was the highest. But because the effect of platinum particles on the responding current of detection of hydrogen peroxide was not significant only the ferrocene was used to modify the carbon paste electrode to apply to glucose biosensor in this study. The optimum operating conditions were -0.2 V operating potential, 500 rpm stirring rate and in 0.05M PBS buffer solution ( pH = 7.4 ). For the glucose biosensor, at 30 ℃, -0.2V operating potential, and in 0.05 M PBS buffer solution( pH = 7.4 ), the detection limit was 0.06 mM C 6 H 12 O 6 ; the linear range was 0.06 ~ 2.0 mM C 6 H 12 O 6 ; R 2 = 0.992 and the sensitivity was 83.1 μA/cm 2 mM C 6 H 12 O 6. REFERENCES 1. P. C. Pandey and S. Upadhyay, “Bioelectrochemistry of Glucose Oxidase Immobilized on Ferrocene Encapsulated Ormosil Modified Electrode,” Sensors and Actuators B, Vol.76,193 (2001). 2. M. A. Kim and W.-Y. Lee, “Amperometric Phenol Biosensor Based on Sol-Gel Silicate/Nafion Composite Film,” Analytica Chimica Acta, Vol.479, 143 (2003). 3. Y.-M. Uang and T.-C. Chou, “Fabrication of Glucose Oxidase/Polypyrrole Biosensor by Galvanostatic Method in Various pH Aqueous Solutions,” Biosensors and Bioelectronics, Vol.19, 141(2003). (A) (B) Fig. 2 TB graphs of the carbon paste electrodes for different ratios of ferrocene to graphite carbon powders; the ratios of ferrocene to graphite carbon powders are 〔 (A) 0:10(unmodified carbon paste electrode) (B)1:9 (C) 2:8 (D)3:7(E) 4:6(F) 5:5 〕 ; the operating potential = –0.2 V; 10 μL of 50mM H 2 O 2 is injected per 100 seconds