Engineering of thermo-responsive polymeric hydrogels for fluorescent color switching

Abstract

Stimuli-responsive hydrogels with decent optical properties are a promising class of polymeric materials for a range of technological applications such as photonic, biomedical and analytical devices due to the high degree of freedom of shapes, portability, and processibility. In this study, we developed a hydrogel-based fluorescent thermometer using organic dyes labeled temperature-responsive copolymer system. Poly(N-isopropylacrylamide) (PNIPAM) was chosen as a thermally-responsive spacer between blue and green emitting dyes in order to make conformational change by temperature, while randomly polymerized acrylates were used to regulate water swelling ratio of the hydrogel. The spatial proximity of F$ddot{o}$rster resonance energy transfer (FRET) between donors and acceptors incorporated in the hydrogel can be tuned via thermo-induced collapsing and swelling of the platform at the lower critical solution temperature of PNIPAM, leading to the facile modulation of FRET efficiencies. In addition, our hydrogel system showed excellent reversibility, indicating an ideal platform for biological and environmental applications.