Fluorescence Turn-on Detection of Alkaline Phosphatase Activity and Al3+ Using Vitamin B6 Cofactor Conjugated GSH Capped Mn-doped ZnS Quantum Dots.

The glutathione (GSH) functionalized Mn-doped ZnS quantum dots (GSH_Mn_ZnS QDs) was conjugated with pyridoxal 5'-phosphate (PLP). The -CHO group of vitamin B6 cofactor PLP interacted with the -NH2 group of GSH functionalized Mn_ZnS QDs. The conjugation of PLP quenched the fluorescence emission of GSH_Mn_ZnS QDs at 601 nm. Addition of alkaline phosphatase (ALP) catalytically dephosphorylated the PLP into pyridoxal that restored the fluorescence emission of GSH_Mn_ZnS QDs. With a sensitivity of 0.035 U/L, the PLP conjugated GSH_Mn_ZnS QDs was applied to quantify ALP activity in human serum and plasma. Further, the developed nanoprobe PLP conjugated GSH_Mn_ZnS QDs was also applied to detect Al3+. The complexation-induced fluorescence enhancement was observed at 492 nm upon the interaction of Al3+ with the PLP conjugated GSH_Mn_ZnS QDs. Without any interference from other tested metal ions, this nanoprobe can be employed to detect Al3+ down to 2.30 µM.