Benzoxazine-based fluorescent probes with different auxochrome groups for cysteine detection.

Three 5 H -benzo[a]phenoxazin-5-one-based (benzoresorufin and nile-red) Cysteine (Cys) detection probes have been comparatively designed and synthesized in this paper. The optical experiments exhibit probe 1b with a crotonoyl group has no response toward Cys; while probes 1a and 1c have the same reaction site (acryloyl group), their optical responses to Cys are quite different. The benzoresorufin-based-probe 1a shows a turn-on fluorescence response (118-fold) to Cys at 631 nm and affords a very low detection limit (DL = 19.8 nM). Compared with probe 1a , the nile-red-based probe 1c displays gradually diminishing fluorescence intensity with increased Cys concentration at 665 nm. And the notable different fluorescence response mechanisms of probes 1a and 1c toward Cys can be interpreted by HRMS and time-dependent density functional theorety (TDDFT) calculations. Furthermore, both of the two probes indicate high sensitivity and selectivity toward Cys over other similar structured amino acids including homocysteine (Hcy) and glutathione (GSH). Further cellular applications of the two probes have been successfully performed in HeLa cells. Image 1 • Three Cys probes 1a − c based on benzoxazine (benzoresorufin and nile-red) were comparatively designed, synthesized and investigated, and the mechanism was proposed. • Their different responses to Cys could indicate that the same fluorophore with different auxochrome groups and detection groups have different properties. • Probes 1a and 1c exhibited high selectivity for Cys, and 1a had a low detection limit of 19.8 nM. • Off-on and attenuation response; long emission wavelength; cell imaging. [ABSTRACT FROM AUTHOR]