An "on-off-on" selective fluorescent probe based on nitrogen and sulfur co-doped carbon dots for detecting Cu and GSH in living cells.

The abnormal level of Cu or GSH can cause variety of neurodegenerative diseases in humans. Thus, the selective and sensitive detection of Cu and GSH has inspired intensive research efforts in biological sample analysis fields. Herein, an "on-off-on" fluorescent probe based on nitrogen and sulfur co-doped carbon dots (N,S-CDs) has been successfully prepared for the detection of Cu and GSH. The "turn-off" process of fluorescence in the presence of Cu ions was induced by forming a non-luminescent ground state complex due to the interaction between surface groups of the probe and Cu ions. Moreover, the strong coordination between GSH and Cu could destroy the structure of the complex and restore the fluorescence to "turn-on". This fluorescent probe had excellent selectivity and high sensitivity toward Cu and GSH with the limits of detection (LODs) of 38 nM and 41 nM. More importantly, the as-prepared N,S-CDs served as an efficient fluorescent probe for not only detecting Cu ions in lake water and tap water, and GSH in BSA solution, but also sensing Cu and GSH in living cells. Therefore, these N,S-CDs could be considered as a promising fluorescence probe candidate for environmental monitoring and biological imaging.