Thermo-sensitivity of hybrid nanogels for specific endogenous hydrogen sulfide detection and efficient flash chill treatment

Abstract

Thermo-responsive nanogels, poly(NIPAM–AAM) were prepared by a facile method of free radical one-pot precipitation based on monomeric N-isopropylacrylamide (NIPAM). At the same time, surface carboxyl group-modified fluorescent conjugated polymer nanoparticles (PNPs_–COOH) were immobilized in the nanogel networks by hydrogen bonding to show bright green photoluminescence and outstanding thermo-responsive properties with a typical two-phase Tai Chi structure. Poly(NIPAM–AAm)–PNPs_–COOH displays a larger change of hydrodynamic diameter (D_h) and a reversible volume transition from ∼150 nm at 40 °C to ∼1.0 μm at 4 °C. The change will cause apoptosis of cells to finish flash chill treatment. Meanwhile, the fluorescence of poly(NIPAM–AAm)–PNPs_–COOH demonstrates reversible quenching and recovery with the expansion and collapse of the nanogel network induced by temperature changes. In addition, when adding Fe³⁺, the fluorescence of poly(NIPAM–AAm)–PNPs_–COOH can be quenched due to the chelation between the PNPs_–COOH and Fe³⁺ and then recovered in the presence of hydrogen sulfide because the chelate is broken; this was attributed to the stronger affinity between Fe³⁺ and S²⁻. Therefore, the fluorescence nanoplatform, Fe³⁺/poly(NIPAM–AAm)–PNPs_–COOH, was successfully used to detect endogenous hydrogen sulfide in living A549 cells.