A novel electrochemical biosensor for the detection of uric acid and adenine

Abstract

A novel electrochemical biosensor for the detection of uric acid and adenine was prepared based on a gel containing multi-walled carbon nanotubes and room-temperature ionic liquid of 1-octyl-3-methylimidazolium hexafluorophosphate. The electrochemistry of uric acid and adenine was studied in this gel modified electrode. There was a significant two-way electrocatalytic activity upon both oxidation and reduction of uric acid. Similar to a bare glassy carbon electrode, uric acid undergoes a 2e,2H+ oxidation in phosphate buffer in the modified electrode. A diimine, the oxidation product of uric acid, was found to be an unstable intermediate, which was converted by a follow-up hydration reaction to an imine alcohol, with the reaction rate constant of 8.5 +/- 0.3 M-1·s-1 according to Nicholson's theory. Under optimum conditions, linear calibration graphs were obtained over the concentration range of 1.0×10-7 M - 1.0×10-5 M (uric acid) and 1.0×10-5 M - 6.0×10-4 M (adenine). Based on the signal-to-noise ratio of 3, the detection limits of the current technique was found to be as low as 9.0×10-8 M (uric acid) and 2.0×10-6 M (adenine), respectively. This novel biosensor was successfully applied for the assay of uric acid in human urine. Because of its good stability and long-term durability, such a gel modified electrode can provide a simple and easy approach for sensitive detection of uric acid and adenine.