o-Phenylenediamine/gold nanocluster-based nanoplatform for ratiometric fluorescence detection of alkaline phosphatase activity

This study demonstrates a novel and convenient ratiometric fluorescent method for the detection of alkaline phosphatase (ALP) activity. Amino-functionalized mesoporous silica nanoparticle-gold nanoclusters (MSN-AuNCs) nanocomposites were integrated with o-phenylenediamine (OPD) to form a ratiometric fluorescence nanoplatform. The presence of ALP induced the generation of quinoxaline (QX) derivative which called 3-(dihydroxyethyl)furo[3,4-b]quinoxaline-1-one (DFQ) with strong fluorescence emission at 450 nm, while the orange-red fluorescence of MSN-AuNCs at 580 nm was slightly quenched. Meanwhile, an obvious fluorescence color change from orange-red to purple and finally to blue can be observed by naked eyes with the increasing of ALP concentration. Therefore, employing the fluorescence emission of DFQ at 450 nm as the reporter signal and the fluorescence emission of MSN-AuNCs at 580 nm as a reference signal, a sensitive ratiometric detection method for ALP was developed. Quantitative detection of ALP activity in the linear range from 0.2 to 80 U/L with a detection limit of 0.1 U/L can be realized in this way, which endows the assay with high sensitivity enough for practical detection of ALP in human serum samples.