Polarity-switchable photoelectrochemical detection of tyrosinase activity based on enzyme-triggered boronic ester bridging between In2S3 and Cu2ZnSnS4.

Herein, an innovative polarity switchable strategy for photoelectrochemical (PEC) detection is reported by utilizing enzyme-triggered boronic ester bridging between two semiconductors. Monophenol-modified In2S3 is prepared by sequentially coating polyethyleneimine (PEI) and covalently conjugating 4-hydroxyphenylacetic acid (PhOH) on In2S3, whereas dihydroxy-modified Cu2ZnSnS4 is prepared through surface coating of chitosan (CS). Under the catalysis of tyrosinase (TYR), monophenol groups of In2S3@PEI-PhOH undergo the conversion to o-diphenol groups. With the aid of 1,4-phenylboronic acid, boronate ester bridges form between TYR-treated In2S3@PEI-PhOH and Cu2ZnSnS4@CS, so In2S3 can be anchored on the Cu2ZnSnS4@CS-modified electrode surface. As a result, the formation of p-n heterojunctions on the photoelectrode can reverse the photocurrent polarity, enabling polarity switchable PEC detection of TYR activity. The linear range is from 0.01 to 5 U mL-1, and the detection limit is 0.0015 U mL-1 for TYR activity detection. The established method is successfully employed for TYR activity detection in human serum samples.