A self-adaptive multi-color fluorescent pH probe with the ability of whole cell imaging

Fluorescent pH probes are promising for both in vitro and in vivo pH detections in chemical and biochemical systems. Previously, the multi-color and whole cell pH sensing is a challenge for conventional fluorescent nanomaterials. In this work, we report an N, S co-doped carbon dots (N, S-CDs)-based fluorescent pH probe that can response to different incident light with tunable wavelength. The emission wavelength is tunable and correlated to the excitation wavelength, enabling self-adaptive multi-color sensing. The N, S-CDs was synthesized by a one-step hydrothermal method utilizing glucose, ammonium persulfate and ethylenediamine as precursors. The fluorescence of N, S-CDs shows a good linear relationship against pH values from 3.0 to 10.0 with a linear correlation coefficient of 0.996. The good biocompatibility and small size fulfill the demand of whole cell intracellular imaging. We have demonstrated that the N, S-CDs have successfully applied in HepG2 cells for the self-adaptive multi-color imaging.