A performance comparison of choline biosensors:: anodic or cathodic detections of H2O2 generated by enzyme immobilized on a conducting polymer

Amperometric choline biosensors were fabricated by the covalent immobilization of an enzyme of choline oxidase (ChO) and a bi-enzyme of ChO/horseradish peroxidase (ChO/HRP) onto poly-5,2':5',2"-terthiophene-3'-carboxylic acid (poly-TTCA) modified electrodes (CPMEs). A sensor modified with ChO utilized the oxidation process of enzymatically generated H2O2 in a choline solution at +0.6v The other one modified with ChO/HRP utilized the reduction process of H2O2 in a choline solution at -0.2 V. Experimental parameters affecting the sensitivity of sensors, such as pH, applied potential, and temperature were optimized. A performance comparison of two sensors showed that one based on ChO/HRP/CPME had a linear range from 1.0 X 10(-6) to 8.0 X 10(-5) M and the other based on ChO/CPME from 1.0 x 10(-6) to 5.0 x 10(-5) M. The detection limits for choline employing ChO/HRP/CPME and ChO/CPME were determined to be about 1.0 x 10(-7) and 4.0 x 10(-7) M, respectively. The response time of sensors was less than 5 s. Sensors showed good selectivity to interfering species. The long-term storage stability of the sensor based on ChO/HRP/CPME was longer than that based on ChO/CPME. (C) 2003 Elsevier B.V. All rights reserved.