Ag-Ion-Modified Au Nanoclusters for Fluorometric Analysis of Alkaline Phosphatase

Alkaline phosphatase (ALP) has been regarded as one vital biomarker in clinical diagnoses and biomedical studies, and fabrication of sensitive and effective approaches for ALP analysis is of extraordinary significance. Herein, a ratio fluorometric platform was constructed for ultrasensitive detection of ALP utilizing silver ion (Ag+)-modified gold nanoclusters (Ag-AuNCs) and o-phenylenediamine (OPD) as signal indicators. The AuNCs fluorescence was greatly enhanced via simply modifying with Ag+. With the addition of ALP, the substrate ascorbic acid 2-phosphate (AAP) was transformed to ascorbic acid (AA). Then, a redox reaction between KIO3 and AA was employed to produce I-2/I- and dehydroascorbic acid (DHA). The I-2/I- caused the notable fluorescence quenching of Ag-AuNCs at 600 nm through I- combining with Ag+ and I-2 triggered oxidative etching and aggregation of Ag-AuNCs. Meanwhile, DHA reacted with OPD to form a fluorescent quinoxaline derivative (QXD) with apparent emission at 438 nm. Therefore, by measuring the fluorescence intensity ratio (F-438/F-600) of this fluorometric platform, we sensitively monitored the ALP activity with a low detection limit of 0.0035 U L-1. Moreover, the practical application was demonstrated by ALP analysis in human serum with high accuracy and reliability, which endowed this platform as a competitive alternative for ALP-related diagnostic analysis.