Turn-on fluorescence measurement of acid phosphatase activity through an aggregation-induced emission of thiolate-protected gold nanoclusters.

A fluorescence method was developed for a turn-on measurement of acid phosphatase (ACP) activity. It was found that cerous ion (Ce3+) could lead to an enhancement of glutathione protected gold nanocluster fluorescence through an aggregation-induced-emission (AIE) process, while its higher valent counterpart ceric ion (Ce4+) could not. In a weakly acidic environment, ACP catalyzed the dephosphorylation of a phosphate ester of ascorbic acid, with a generation of ascorbic acid (AA). AA reduced Ce4+ into Ce3+, which subsequently enhanced the nanocluster fluorescence. This kind of turn-on fluorescence linearly related to the ACP activity in the range of 0.005-2.4 U/L, with a limit of detection as 0.001 U/L. Human serum samples were measured after a trichloroacetic acid treatment and a simple dilution. The whole analyses were accomplished in 1.5 h with results in good accordance with a reference method.