A TICT based two-photon fluorescent probe for cysteine and homocysteine in living cells.

A two-photon fluorescent probe ( NQ ) for cysteine (Cys) and homocysteine (Hcy) was developed based on twisted-intramolecular-charge-transfer (TICT) mechanism. NQ showed excellent “OFF–ON” fluorescence (at 540 nm) detection signal on addition of Cys/Hcy with high selectivity. The detection mechanism was successfully proved by theoretical calculations, viscosity dependent fluorescence and time resolved fluorescence spectra. NQ exhibits large two-photon absorption (TPA) cross-section with Cys/Hcy (580 and 710 GM) at nearly 800 nm, respectively. Cell-culture results indicated that NQ was cell-permeable and could be used to detect Cys/Hcy with low cytotoxicity under two-photon excitation in living cells. To our best knowledge, NQ is the first TICT based two-photon fluorescent probe for Cys/Hcy. [ABSTRACT FROM AUTHOR]