Direct electrochemistry of horseradish peroxidase immobilized on a colloid/cysteamine-modified gold electrode

Direct electron transfer of immobilized horseradish peroxidase on gold colloid and its application as a biosensor were investigated by using electrochemical methods. The An colloids were associated with a cysteamine monolayer on the gold electrode surface. A pair of redox peaks attributed to the direct redox reaction of horseradish peroxidase (HRP) were observed at the HRP/Au colloid/cysteamine-modified electrode in 0.1 M phosphate buffer (pH 7.0). The surface coverage of HRP immobilized on Au colloid was about 7.6 x 10(-10) mol/cm(2). The sensor displayed an excellent electrocatalytic response to the reduction of H2O2 without the aid of an electron mediator. The calibration range of H2O2 was 1.4 mu M to 9.2 mM with good linear relation from 1.4 mu M to 2.8 mM. A detection limit of 0.58 mu M was estimated at a signal-to-noise ratio of 3. The sensor showed good reproducibility for the determination of H2O2. The variation coefficients were 3.1 and 3.9% (n = 10) at 46 mu M and 2.8 mM H2O2, respectively. The response showed a Michaelis-Menten behavior at higher H2O2 concentrations. The K-M(app) value for the H2O2 sensor was found to be 2.3 mM. (C) 2000 Academic Press.