Ratiometric fluorescent sensor based on MoS₂ QDs and AuNCs for determination and bioimaging of alkaline phosphatase

Herein, a ratiometric fluorescent sensor based on MoS₂ quantum dots (QDs) and glutathione-capped gold nanoclusters (AuNCs) was developed for determination and imaging of alkaline phosphatase (ALP). The sensor was developed by covalently linking QDs with AuNCs to form stable MoS₂@AuNCs nanohybrids that exhibited the blue fluorescence of MoS₂ QDs and the red fluorescence of AuNCs. In the presence of Ce³⁺, the fluorescence intensity of AuNCs was increased due to the aggregation-induced emission enhancement (AIEE), while that of MoS₂ QDs remained unchanged, thus could be used as a reference signal. After adenosine 5'-monophosphate (AMP) and ALP were introduced into the system, AMP was hydrolyzed to adenosine and phosphate ions (PO₄^3-). Owing to higher affinity between Ce³⁺ and PO₄^3-, the AIEE effect was inhibited, in turn resulting in the decrease of AuNCs fluorescence. The developed ratiometric fluorescent sensor had a linear response to ALP concentration ranging from 0.5 to 50 U L^-1 with a detection limit (LOD) of 0.08 U L^-1. Moreover, the sensor had low cytotoxicity and was successfully employed in lysosome localization and bioimaging of intracellular ALP in living cells.