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

A new on-off assay for alkaline phosphatase (ALP) detection using molybdenum oxide quantum dots (MoOx QDs) was developed 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”).88