A new copper mediated on-off assay for alkaline phosphatase detection based on MoOx quantum dots

Abstract

We present a new on-off assay for alkaline phosphatase (ALP) detection using molybdenum oxide quantum dots (MoOx QDs) based on three favorable properties: the quenching ability of Cu2+ on MoOx QDs, the strong binding affinity between Cu2+ and PPi, and the catalysis ability of ALP to hydrolyze PPi to orthophosphate (Pi). Benefiting from the strong affinity of Cu2+ and PPi, the effective quenching of MoOx QDs by Cu2+ was hampered when PPi was added into the system containing MoOx QDs and Cu2+, leading to a significant photoluminescence enhancement (“ON”). Further addition of ALP, PPi was catalytically hydrolyzed into Pi, which would disable the formation of Cu2+-PPi complex and release free Cu2+, resulting in photoluminescence quenching (“OFF”). The on-off assay allows the analysis of PPi and ALP by measuring the photoluminescence intensity, and quantitative detection of ALP in a linear range from 0.1 to 5.0 U/L with the detection limit of 0.02 U/L (3σ/K) is realized. Moreover, the present assay was successfully applied in ALP inhibitor screening and ALP detection in diluted human serum samples, and satisfactory recoveries between 99.6% and 103.0% were obtained. The on-off photoluminescence assay shows many merits, including convenient operation, cost-saving, high sensitivity and superior selectivity, which allow the assay for ALP detection in real human serum samples.