The Detection of Glucose for the Carbon Paste Electrode Modified with Ruthenium Hexacyanoferrate Kuo-Hsiang Liao ( 廖國翔 ), Chih-Ying Wu ( 巫致穎 ), 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 Both the hydrogen peroxide sensor and glucose biosensor are important research subjects. A study was conducted to use the ruthenium hexacyanoferrate( Ⅱ ) to modify the carbon paste electrode which was used as the working electrode to detect the responding current of reduction of hydrogen peroxide in the PBS buffer solution( pH = 7.4 )and the sensitivity of detection of hydrogen peroxide was determined from the responding current and consequently, the concentration of the glucose could be determined. The TB (Time Base) graphs for different operating potentials, stirring rates, and pH values were plotted to determine the optimum operating conditions. The results showed that the responding current for the carbon paste electrode modified with the ruthenium hexacyanoferrate( Ⅱ ) was elevated significantly. At 30 ℃, -0.2V operating potential, 600rpm stirring rate and in 0.05 M PBS buffer solution( pH = 7.4 ), when the carbon paste electrode was modified with the ruthenium hexacyanoferrate( Ⅱ ) [ruthenium hexacyanoferrate( Ⅱ ) : graphite carbon powders = 3 : 7 ( weight ratio )], the detection limit was 0.02 mM H 2 O 2, the linear range was 0.02 ～ 2.7 mM H 2 O 2, R 2 =0.9996, and the sensitivity was μA/cm 2 ּmM H 2 O 2. For the glucose biosensor, the detection limit was 0.02 mM C 6 H 12 O 6, the linear range was 0.02~2.56 mM C 6 H 12 O 6 (R 2 =0.999), and the sensitivity was 4.11 µA/cm 2 ． mM C 6 H 12 O 6. The optimum operating conditions are -200mV operating potential, 600rpm stirring rate and in 0.05 M PBS buffer solution( pH = 7.4 ) [ruthenium hexacyanoferrate( Ⅱ ) : graphite carbon powders = 3 : 7 ( weight ratio )]. INTRODUCTION ： A study was conducted to use the ruthenium hexacyanoferrate( Ⅱ ) 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. At 30 ℃, the TB (Time Base) graphs for the carbon paste electrode modified with ruthenium hexacyanoferrate [ruthenium hexacyanoferrate( Ⅱ ) : graphite carbon powders = 3 : 7 ( weight ratio )] were plotted to evaluate the effect of reaction parameters on the responding current of detection of hydrogen peroxide. After the optimum conditions were determined, the carbon paste electrode was used to determine the sensitivity of detection of hydrogen peroxide and glucose. EXPERIMENTAL SECTION ： ABSTRACT ： CONCLUSIONS ： The results showed that the optimum weight ratio for carbon paste : ruthenium hexacyanoferrate( Ⅱ ) : carbon powders was 1 : 0.3 : 0.7. At 30 ℃, -200mV operating potential, 600rpm stirring rate and in 0.05 M PBS buffer solution( pH = 7.4 ), when the carbon paste electrode was modified with the ruthenium hexacyanoferrate( Ⅱ ), the detection limit was 0.02 mM H 2 O 2, the linear range was 0.02 ～ 2.7 mM H 2 O 2, R 2 =0.9996, and the sensitivity was μA/cm 2 ּmM H 2 O 2. For the glucose biosensor, the detection limit was 0.02 mM C 6 H 12 O 6, the linear range was 0.02~2.56 mM C 6 H 12 O 6 (R 2 =0.999), and the sensitivity was 4.11 µA/cm 2 ． mM C 6 H 12 O 6. The optimum operating conditions are -200mV operating potential, 600rpm stirring rate and in 0.05 M PBS buffer solution( pH = 7.4 ). Preparation of Working Electrode ： 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 cm 0.05 cm 2. Then the ruthenium hexacyanoferrate( Ⅱ ) powders, carbon powders and carbon paste were mixed with the appropriate ratio. 3. 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. Fig 1. CV graphs for (A) carbon paste electrode modified with ruthenium hexacyanoferrate( the range of scanning potential: -0.8 ～ +0.8 V) (B) unmodified carbon paste electrode( the range of scanning potential: -0.6 ～ +0.6 V) 1.M. A. Kim and W.-Y. Lee, “Amperometric Phenol Biosensor Based on Sol-Gel Silicate/Nafion Composite Film,” Analytica Chimica Acta, 479, 143 (2003). 2. M. Yang, J. Jiang, Y. Lu, Y. He, G. Shen and R. Yu, “Functional Histidine/Nickel Hexacyanoferrate Nanotube Assembly for Biosensor Applications,” Biomaterials, 28, 3408 (2007). 3. C. Guo, F. Hu, C. M. Li and P. K. Shen, “Direct Electrochemistry of Hemoglobin on Carbonized Titania Nanotubes and Its Application in a Sensitive Reagentless Hydrogen Peroxide Biosensor,” Biosensors and Bioelectronics, 24, 819 (2008). 4. X. Chen, J. Chen, C. Deng, C. Xiao, Y. Yang, Z. Nie and S. Yao, “Amperometric Glucose Biosensor Based on Boron-Doped Carbon Nanotubes Modified Electrode,” Talanta, 76, 763 (2008). REFERENCES ： Ruthenium Hexacyanoferrate Powders Preparation of Ruthenium Hexacyanoferrate ： 30 mM Potassium Hexacyanoferrate 5 mL 3 mM Ruthenium Chloride Hydrate 50 mL Centrifuging Repeat Centrifuging Three Times Drying ruthenium hexacyanoferrate carbon powder ( appropriate ratio ) A powder appropriate A powder adding carbon paste 4. After the above mentioned carbon paste electrode was dried, the 3μL glucose oxidase solution( 3mg of glucose oxidase was dissolved in 200μL 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. Glucose Oxidase Nafion PVC cover ( ) Fig. 2 The TB graphs of carbon paste electrode for detection of H 2 O 2 at different operating potentials ( ruthenium hexacyanoferrate : graphite carbon powders = 3 : 7); the operating potentials are [ (A) –50mV (B) –100mV (C) –200mV (D) –300mV ] Fig. 4 The TB graphs of carbon paste electrode for detection of H 2 O 2 at different pH values of PBS buffer solution ( ruthenium hexacyanoferrate : graphite carbon powders = 3 : 7); the pH values are [ (A) pH = 4 (B) pH = 5 (C) pH = 6 (D) pH = 7 (E) pH = 7.4 (F) pH = 8 ] Fig. 5 The TB graph of glucose biosensor for detection of the detection limit of glucose (ruthenium hexacyanoferrate( Ⅱ ) : graphite carbon powders = 3 : 7). Fig. 3 The TB graphs of carbon paste electrode for detection of H 2 O 2 at different stirring rates ( ruthenium hexacyanoferrate : graphite carbon powders = 3 : 7); the stirring rates are [ (A) 300rpm (B) 400rpm (C) 500rpm (D) 600rpm(E) 700rpm] Fig. 6 The TB graphs of glucose biosensor for detection of glucose ( ruthenium hexacyanoferrate( Ⅱ ) : carbon powders = 3 : 7); At 30 ℃ ; the operating potential = –200 m V; in 0.1 M KCl of 5 mL 0.05 M PBS buffer solution ( pH=7.4 ); stirring rate=600 rpm; 16μL of 100mM glucose is injected per 100 seconds