β-Cyclodextrin modified silver nanoclusters for highly sensitive fluorescence sensing and bioimaging of intracellular alkaline phosphatase.

In this paper, silver nanoclusters (AgNCs) were synthesized by one facile, low-cost and green method with histidine acting as the stabilizer and ascorbic acid performing as reducing agent. AgNCs displayed excellent fluorescence property and good biocompatibility and were further functionalized by β-cyclodextrin (CD-AgNCs) for the highly sensitive detection of alkaline phosphatase (ALP) activity. ALP catalyzed the dephosphorylation of p-nitrophenylphosphate (NPP) to produce p-nitrophenol (NP), and NP can effectively quench the fluorescence of CD-AgNCs via the inner filter effect (IFE) due to the UV-vis absorption spectrum of NP had considerable overlap with the excitation spectrum of CD-AgNCs. Benefiting from the IFE and the host-guest interaction between CD and NP, this CD-AgNCs based system for ALP activity analysis displayed a good linear range of 0.02-10.0 U L and the detection limit as low as 0.0046 U L. In addition, this proposed strategy also showed satisfactory performance for ALP analysis in human serum samples and bioimaging of intracellular ALP in living cells, indicating the great application prospect of this system for ALP activity analysis in medical related researches.