A room-temperature phosphorescence sensor for the detection of alkaline phosphatase activity based on Mn-doped ZnS quantum dots

A convenient and efficient biosensor for detection of alkaline phosphatase (ALP) activity was built with Mn-ZnS quantum dots (QDs) as the phosphorescent probe and adenosine 5'-monophosphate (AMP) as the substrate. Eu3+, which could coordinate with surface carboxyl group of Mn-ZnS QDs, was added into Mn-ZnS QDs to form Mn-ZnS QDs/Eu3+ nanocomposites, which quenched the RTP of Mn-ZnS QDs through photoinduced electrontransfer (PIET). After ALP and AMP were added into the system, under the hydrolytic catalysis of ALP, AMP was rapidly converted into adenosine and phosphate ions. The higher affinity of phosphate ions to Eu3+ than QDs resulted in the formation of a more stable composite, and subsequently, Eu3+ was desorbed from the surfaces of Mn-ZnS QDs, which restored the RTP of Mn-ZnS QDs. Under the optimal conditions, the RTP intensity of the Mn-ZnS QDs (Delta RTP) was well linearly related to the logarithm of the ALP activity, with a detection range of 0.15-18 U L-1 and a detection limit of 0.065 U L-1. This phosphorescent sensor avoided interference from auto-fluorescent and scattering light in real biological samples and was highly sensitive to ALP.