FRET Effect between Fluorescent Polydopamine Nanoparticles and MnO2 Nanosheets and Its Application for Sensitive Sensing of Alkaline Phosphatase

As an essential and universal hydrolase, alkaline phosphatase (ALP) has been identified as a crucial indicator of various diseases. Herein, we, for the first time, expanded the application of fluorescent polydopamine (F-PDA) nanoparticles to nanoquencher-based biosensing system, as well as discovered the reversible quenching effect of manganese dioxide (MnO2) nanosheets on the fluorescence of F-PDA nanoparticles and intensively confirmed the quenching mechanism of Förster resonance energy transfer by using transmission electron microscopy, UV–vis, Fourier transform infrared spectroscopy, and fluorescence lifetime experiments. By means of the ALP-triggered generation of ascorbic acid (AA) from the substrate ascorbic acid 2-phosphate, the AA-triggered reduction of MnO2 nanosheets to Mn2+, as well as the clear quenching mechanism of F-PDA nanoparticles by MnO2 nanosheets, we have developed a label-free, low-cost, visual, and facile synthetic fluorescent biosensor for convenient assay of ALP activity. The fluorescent bioassay shows a good linear relationship from 1 to 80 mU/mL (R2 = 0.999), with a low detection limit of 0.34 mU/mL, and the excellent applicability in human serum samples demonstrates potential applications in clinical diagnosis and biomedical research.