Sensitivity evaluation of NBD-SCN towards cysteine/homocysteine and its bioimaging applications

• We report an easily preparative fluorescent probe with only one-step synthetic procedure for the detection of cysteine/homocysteine.
• This probe possesses high selectivity toward cysteine/homocysteine.
• This probe shows a rapid fluorescent response toward cysteine and high sensitivity toward cysteine and homocysteine with a detection limit of 2.99 and 1.43 nM, respectively.
• The intracellular imaging of biothiols has been demonstrated in live Raw 264.7 cells.

A push–pull fluorogenic reagent, NBD-SCN, was applied for specific detection of cysteine (Cys) and homocysteine (Hcy). Replacing thiocyanato group with Cys/Hcy increased the push–pull characteristic of the probe and resulted in emission of fluorescence. The fluorescent response of the probe toward Cys/Hcy was significantly higher than toward glutathione and other amino acids. The probe showed a 470- and 745-fold fluorescence enhancement at 550 nm and detection limit of 2.99 and 1.43 nM for Cys and Hcy, respectively. Time-dependent fluorescence assays showed that the fluorescence intensity reached a plateau within 20 s after addition of Cys and within 10 min after addition of Hcy. Furthermore, the fluorescence images of Cys/Hcy in Raw 264.7 cells were obtained after adding this probe to the cells. These results indicate that NBD-SCN not only possesses good selectivity and sensitivity for Cys/Hcy but also can penetrate cells for Cys/Hcy bioimaging.