Specific binding assay for biotin based on enzyme channelling with direct electron transfer electrochemical detection...

A model 'homogeneous' format enzyme channelling specific binding assay for biotin based on peroxide-sensitive horseradish peroxidase mediatorless enzyme electrodes is described. The procedure involved the immobilisation of avidin onto the surface of printed carbon horseradish peroxidase (HRP) enzyme electrodes and the competitive binding of biotin and biotinylated glucose oxidase. Upon addition of glucose, hydrogen peroxide was generated via the glucose oxidase label. Direct electron transfer between the electrodes and HRP resulted in the detection of H2O2 by electroenzymic reduction at +50 mV vs Ag/AgCl. The cathodic current response could be measured in the presence of excess biotinylated glucose oxidase by incorporation of catalase in homogeneous solution to scavenge H2O2 generated in the bulk before it diffused to the electrode surface. The assay showed greatest sensitivity over the range of biotin concentrations 0.07 to 2 micrograms ml-1 in the presence of 10 micrograms ml-1 excess biotinylated glucose oxidase in the bulk solution.