Fluorescent Polymer-MoS2-Embedded Microgels for Photothermal Heating and Colorimetric Monitoring

Abstract

Photothermal heating with accurate monitoring of local temperature in complex biological fluids is crucial for therapeutic accuracy. Herein, photothermal microgels are developed to heat microscopic volumes through photothermal conversion and report the local temperature with a colorimetric response. The microgels consist of poly(ethylene glycol)-based hydrogels, which integrate temperature-responsive block-copolymer-grafted MoS2 nanosheets (BCP-grafted MoS2 NSs). The MoS2 NSs are used as a fluorescence quencher as well as an efficient photothermal agent, with their surface decorated with three distinct temperature-responsive BCPs containing blue-, green-, and red-fluorescent dyes. Upon irradiation of near-infrared light, MoS2 NSs convert the radiation into heat, and the BCPs change their conformation depending on the local temperature, selectively activating Forster resonance energy transfer of the three dyes. The use of three distinct BCPs and dyes enables the measurement of temperature in a wide range (i.e., from 25 to 50 degrees C). Importantly, the hydrogel matrix excludes molecules larger than the limiting mesh size so that BCP-grafted MoS2 NSs remain free from contamination against large adhesive proteins such as albumin, thus maintaining their sensitivity even in complex fluids.