A hydrothermal method has been employed to synthesize a green and one-pot carbon dots-based sensor for ratiometric monitoring and imaging lysosomal pH in living cells. The carbon dots were directly functionalized by abundant amino groups during synthesis and exhibited dual emission bands at 439 and 550 nm under single-wavelength excitation of 380 nm without any additional modification. In addition to its small size, the established sensor had good biocompatibility. Owing to its abundant amino groups and good hydrophilicity, the sensor is able to target lysosome with high Pearson's colocalization coefficients (0.935 and 0.924) and responds to change of lysosomal pH in living cells. It also had excellent pH sensitivity and reversibility, and anti-interference capability, thus enabling sensing pH change in intracellular environment in real time, as demonstrated by successful monitoring of lysosomal pH changes during lysosomal alkalization, dexamethasone-induced stimulation, and stress in Michigan Cancer Foundation-7 cells (blue channel, excitation = 405 nm and emission = 419-459 nm bandpass; and yellow channel, excitation = 405 nm and emission = 530-570 nm bandpass). Graphical abstract.
Keywords: Carbon dots; Intracellular pH probe; Living cell imaging; Lysosome; Ratiometric fluorescence sensor.