Development of optical chemosensors based on photochromic polymer nanocarriers

Abstract

The development of optical chemosensors for the photosensing of polarity and pH of aqueous media has been an interesting research area. The application of light-responsive polymer nanoparticles containing photochromic or fluorescent compounds is a novel approach to reaching high sensitivity, fast responsivity, and facile sensing in such optical chemosensors. Light-responsive polymer nanoparticles containing a spiropyran photoswitch and different functional groups were prepared by nanoprecipitation of telechelic homopolymer and copolymer samples in aqueous media. A homopolymer and copolymers based on methyl methacrylate, hydroxyethyl methacrylate, and N,N′-dimethylaminoethyl methacrylate were synthesized by reverse atom transfer radical polymerization using the 4,4′-azobis(4-cyanovaleric acid) initiator. The chemical structure and molecular weight of the samples were investigated by proton nuclear magnetic resonance. The size and morphology investigation of the light-responsive nanoparticles by dynamic light scattering and field-emission scanning electron microscopy showed spherical polymer nanoparticles with a size range of 29–47 nm. Photochromism and fluorescence characteristics at different pH values showed potential for application of light-responsive polymer nanoparticles in the development of optical pH chemosensors by colorimetric and fluorometric mechanisms. The isomerization kinetics of spiropyran to merocyanine and the reverse reaction were significantly affected by the pH of the aqueous media, especially in the case of copolymer samples containing tertiary amine groups. To design pH chemosensors for sensing the pH of aqueous media, light-responsive nanoparticles with hydroxyl or amine functional groups and particle sizes of below 100 nm were shown to be highly efficient.