Fluorescent Biosensor for Phosphate Determination Based on Immobilized Polyfluorene–Liposomal Nanoparticles Coupled with Alkaline Phosphatase

Abstract

This work describes the development of a novel fluorescent biosensor based on the inhibition of alkaline phosphatase (ALP). The biosensor is composed of the enzyme ALP and the conjugated cationic polyfluorene HTMA-PFP. The working principle of the biosensor is based on the fluorescence quenching of this polyelectrolyte by p-nitrophenol (PNP), a product of the hydrolysis reaction of pnitrophenyl phosphate (PNPP) catalyzed by ALP. Because HTMA-PFP forms unstable aggregates in buffer, with low fluorescence efficiency, previous stabilization of the polyelectrolyte was required before the development of the biosensor. HTMAPFP was stabilized through its interaction with lipid vesicles to obtain stable blueemitting nanoparticles (NPs). Fluorescent NPs were characterized, and the ability to be quenched by PNP was evaluated. These nanoparticles were coupled to ALP and entrapped in a sol−gel matrix to produce a biosensor that can serve as a screening platform to identify ALP inhibitors. The components of the biosensor were examined before and after sol−gel entrapment, and the biosensor was optimized to allow the determination of phosphate ion in aqueous medium.