A fluorescence and colorimetric dual-mode assay of alkaline phosphatase activity via destroying oxidase-like CoOOH nanoflakes.

Nanozymes are increasingly exploited as components in bioanalysis and diagnostics. Here, we report a fluorescence and colorimetric dual-mode assay for alkaline phosphatase (ALP) activity employing oxidase-like cobalt oxyhydroxide (CoOOH) nanoflakes. Colorless o-phenylenediamine (OPD), a substrate for oxidase, can be oxidized to a product (OxOPD) with yellow color and orange fluorescence in a CoOOH nanoflake solution. But, ascorbic acid (AA) is able to reduce CoOOH to cobalt ion (Co), which causes the decomposition and collapse of the CoOOH nanoflakes, and thereby the CoOOH nanoflakes are deprived of the oxidase-like property. Based on this principle, the fluorescence and colorimetric dual-mode detection of AA was achieved. Alkaline phosphatase (ALP) can make l-ascorbic acid-2-phosphate (AAP) hydrolyze to yield AA. As a result, with the help of AAP, the selective and sensitive dual-mode assay of ALP activity has been realized successfully by using fluorescence and UV-vis absorption spectroscopies. Quantitative analysis of ALP in human serum samples and an ALP inhibitor investigation were performed using this sensing system. Given the economical and sensitive properties, the proposed method based on CoOOH nanoflakes has great potential for not only probing ALP activity in biological systems but also screening potential ALP inhibitors. Meanwhile, in this study, a new insight has been provided into the application of CoOOH nanoflakes in the development of sensitive and convenient sensors.