Carbon felt-based bioelectrocatalytic flow detectors: highly sensitive amperometric determination of hydrogen peroxide using adsorbed peroxidase and thionine.

Horseradish peroxidase (HRP) and thionine (TN) were co-adsorbed onto a porous carbon felt (CF), and the resulting HRP and TN-adsorbed CF (HRP-TN-CF) was successfully used as a working electrode unit of a novel bioelectrocatalytic flow detector for a highly sensitive amperometric determination of hydrogen peroxide (H(2)O(2)). Co-adsorbed TN was essential to enhance the cathodic peak current of H(2)O(2), and the current responses of the HRP-TN-CF-based detector were much larger than those of the HRP-CF-based detector (without TN). When air-saturated 0.1 M phosphate buffer (pH 7.0) was used as a carrier at a flow rate of 3.9 ml/min, cathodic peak currents of H(2)O(2) (sample injection volume, 200 microl) obtained at an applied potential of 0 V (vs. Ag/AgCl) increased linearly up to 50 microM with a detection limit of 0.1 microM. Repetitive 100 sample injection of 100 microM H(2)O(2) induced no serious current decrease, and RSD was 0.41 to 1.21% (n = 100). The HRP-TN-CF retained 42% of its original activity after 8 days of storage in 0.1 M phosphate buffer at 4 degrees C.