A co-precipitation strategy for making a ratiometric pH nanosensor for intracellular imaging

A core-shell ratiometric pH nanosensor for intracellular imaging was made using a facile co-precipitation strategy. Fluorescein isothiocyanate (FITC), a pH sensitive probe with green fluorescence emission, was first conjugated to amino-terminated polystyrene (PS-NH2). In the co-precipitation method, the FITC-PS-NH2, polystyrene, amphiphilic poly(styrene-co-maleic anhydride) and the reference fluorochrome, 5,10,15,20-tetrakis(pentafluorophenyl) porphyrin, were used to form nanosize hydrophobic cores in an aqueous phase. Finally, poly-l-lysine was selected and attached to the cores through electrostatic forces to improve the cytoplasmic compatibility of the nanoparticles. The prepared FITC doped polymer nanoparticles exhibited excellent ratiometric luminescence responses to pH change and had exceptional intracellular imaging performance as well. Using the prepared nanosensors, a sensing approach for the semi-quantitative pH detection of living cells was set up, revealing the potential applications in biological and biomedical pH detection.