Developed a ratiometric fluorescence pH nanosensor based on label-free carbon dots for intercellular lysosome imaging and water pH monitoring with a smartphone

Abstract It is necessary to measure lysosomal pH in living cells in order to maintain the normal performance of cell functions. Herein, a novel ratiometric fluorescence nanosensor based on carbon dots for lysosomal pH sensing was successfully developed via one-pot solvothermal means. The CDs have two pH-dependent emission wavelengths locating at 415 and 555 nm with distinct fluorescence color change switching between blue and yellow from pH 3.0 to 8.0. Due to its plentiful amino groups on the surface, the probe is lysosome-targeted. It is demonstrated that intensity ratios (F555/F415) against pH = 3.0–8.0 are fitted with the Boltzmann equation with a pKa of 5.47 matched well with lysosomal pH. Because of the merits of great pH sensitivity, selectivity, biocompatibility and photostability, the probe was successfully applied for lysosomal pH detection during cells imaging. Besides, CDs were further used for acidic and neutral water pH sensing by a smartphone in a fast and expedient way.