A simple and sensitive assay of alkaline phosphatase activity in serum by fluorescent silicon nanoparticles based on inner filter effect

A simple and sensitive fluorescence assay was established for the effective monitoring of alkaline phosphatase (ALP) activity in serum based on the inner filter effect (IFE). The facile-synthesized silicon nanoparticles (SiNPs), as the fluorescent indicator of this sensing system, were prepared via a one-pot strategy using N-[3-(trimethoxysiyl)propyl]-ethylenediamine (DAMO) and catechol as the silicon source and reductant, respectively. The zymolyte of this assay, 4-nitrophenyl phosphate (PNPP), would be hydrolyzed with the catalyzation of ALP, resulting in the production of p-nitrophenol (PNP). PNP would induce a significant IFE on the fluorescence emitting from SiNPs due to the overlap of absorption spectrum of PNP and fluorescence excitation spectrum of SiNPs, which was employed to evaluate the activity of ALP. The limit of detection (LOD) and linear range for the present assay are 0.0027 U/L and 0.01-5.0 U/L, respectively. Inorganic ions, enzymes and other biological compounds commonly coexisting in human serum exhibited little influence on the present assay. Good correlation (r = 0.97) between the testing results of real serum samples obtained by the present assay and a commercial reagent kit demonstrates the reliability of this assay. By introducing the enzyme-catalyzed hydrolytic reaction for the generation of energy absorber of fluorescence excitation light, the specific and sensitive activity detection of target enzyme was realized in this work. Moreover, excellent analytical performance of the present assay exhibits broad potential of the facile-prepared fluorescent SiNPs for bioanalysis and clinical diagnosis.