Selective and sensitive fluorescent monitoring of acid phosphatase (ACP) activity under neutral conditions through the ACP enzymatic catalysis of dopamine as a new substrate to polydopamine

Detection of acid phosphatase (ACP), a universal and important enzyme, is crucial in monitoring several diseases. However, the selectivity of ACP detection under neutral conditions is poor. Herein, ACP was found to catalyze dopamine as a new substrate to polydopamine in acidic or neutral conditions, whereas alkaline phosphatase (ALP) failed to serve such function. The catalytic mechanism underlying the formation of polydopamine was investigated. A simple assay for ACP was developed using fluorescent carbon dots as a signal indicator. In the presence of ACP, dopamine polymerization was conducted in situ and carbon dots were quenched through the inner filter effect. This fluorescent bioassay illustrated a good analytical performance with a wide linear range and a detection limit of 0.45 U/L. In particular, ACP showed high selectivity from the interference of ALP under neutral conditions. Furthermore, excellent test recovery in human serum samples demonstrated the predictable applications of this method in clinical and biomedical areas.