Colorimetric sensing of alkaline phosphatase and α-fetoprotein based on the photoinduced oxidase activity of fluorescein

Abstract

A simple and inexpensive colorimetric assay for alkaline phosphatase (ALP) and α-fetoprotein (AFP) has been established by the hydrolysis of fluorescein diphosphate (FDP). We find that FDP as a fluorescein derivative exhibits low photoinduced oxidase activity but can be hydrolyzed to fluorescein with high photoinduced oxidase activity in the presence of ALP. Therefore, an assay was designed to quantitatively analyze ALP activities at concentrations ranging from 0.20 to 80 mU mL⁻¹, which was five-fold more sensitive than a traditional fluorescence assay. Furthermore, we succeeded in detecting AFP in human serum samples by enzyme-linked immunosorbent assay (ELISA) using ALP as the labeling enzyme. In this work, we not only successfully monitored ALP activity but also provided a new analytical strategy based on analyte-induced enhancement of the photoinduced oxidase activity of fluorescein derivatives. This convenient, rapid, universal and sensitive assay provides a promising prospect for clinical diagnosis.