Enzyme-based catechol sensor based on the cyclic reaction between catechol and 1,2-benzoquinone, using l-ascorbate and tyrosinase

A cyclic reaction between catechol and 1,2-benzoquinone takes place by combining the tyrosinase reaction and the chemical reduction of 1,2-benzoquinone to catechol by l-ascorbic acid. Catechol is oxidized by the dissolved oxygen catalysed by the enzyme and its consumption is not compensated for by the chemical regeneration of catechol from 1,2-benzoquinone. The dissolved oxygen thus continues to decrease during the cyclic reaction and consequently the decrease in the reduction current of oxygen is amplified. The amplification factor of 1 X 10−6 M catechol at 0.01 M l-ascorbate and pH 7.0 was found to be 300 when enzyme activity was 20 U ml−1 and the reaction time was 10 min. The calibration graph for catechol with a potato tissue membrane electrode was moved in parallel to a lower concentration range and the detection limit was found to be 5 X 10−8 M (amplification factor 400) when buffer solution of pH 7.0 containing 0.01 M l-ascorbic acid was used.