Monitoring the fluctuations of cysteine activity in living cells using a near-infrared fluorescence probe

Cysteine (Cys) is one of the most common cellular biothiols and is closely implicated in numerous diseases such as edema, psoriasis, Parkinson's disease, and liver damage. Therefore, detecting Cys activity in complex living organisms is highly necessary for diagnosing related diseases. This study synthesized a near-infrared (NIR) Cys-special probe (MCyA) by introducing an acrylate group to the MCyOH fluorophore. Consequently, Cys could precisely and quickly "light up" strong NIR fluorescence (711 nm) by transforming MCyA into MCyOH. Additionally, MCyA was applied to systematically detect dynamic fluctuations of Cys activity in living cells under different stimulation. The observations indicated that the endogenous Cys activity was depressed when HepG2 cells were under oxidative stress status; however, a dramatic expansion of Cys levels in HepG2 cells with omeprazole stimulation. In particular, MCyA has been successfully used to image the upregulation of Cys level in HepG2 cells in the presence of methionine (Met). Overall, MCyA would be a novel and practical tool to study Cys-related physiological and pathological processes.