HIGHLY SENSITIVE AMPEROMETRIC MEASUREMENT OF ALKALINE-PHOSPHATASE ACTIVITY WITH GLUCOSE-OXIDASE AMPLIFICATION

A new method for the amperometric detection of alkaline phosphatase ac tivity based on hydroquinone recycling has been developed. p-Hydroxyph enyl phosphate is hydrolyzed by alkaline phosphatase to hydroquinone w hich, instead of being detected directly, enters an amplification cycl e where it is oxidized to quinone at the electrode surface and then re duced back to hydroquinone by glucose oxidase in the presence of gluco se. The consumption-regeneration cycle of hydroquinone results in an a mplification factor of about 8. A detection limit of 2.5 x 10(-14) M o f alkaline phosphatase was observed. Comparisons with the detection li mits obtained with standard techniques (colorimetry, fluorimetry and c hemiluminescence) were made under the same experimental conditions (sa me enzyme stock solutions, incubation time of 10 min and temperature o f 37 degrees C).