Fluorescent, stimuli-responsive, crosslinked PNIPAM-based microgel

We have synthesized a highly pH and temperature-sensitive, fluorescent, crosslinked poly(N-isopropylacrylamide) (PNIPAM)-based probe via simple free radical emulsion copolymerization, which formed a reversible microgel containing both fluorophores of fluorescein and rhodamine derivatives. We confirmed that the opening of the lactone ring of fluorescein and the lactam ring of rhodamine in the polymer was responsible for the fluorescence changes in basic and acidic conditions, which showed fluorescence emissions at 514 nm (green) and 586 nm (red), respectively. The polymeric microgel exhibited a linear relationship between the ratio of emission intensity and pH windows of pH 2–6 and 7–12. Moreover, the microgel exhibited changes in fluorescence intensity with an alteration of turbidity of the microgel induced by temperature. Moreover, these fluorescence changes could be easily observed by the naked eye, serving as a potential probe for ratiometric microgel detection of pH or temperature.