Tetrahydro[5]helicene fused nitrobenzoxadiazole as a fluorescence probe for hydrogen sulfide, cysteine/homocysteine and glutathione.

Biological thiols including homocysteine (Hcy), cysteine (Cys), hydrogen sulfide (H2S) and glutathione (GSH) play crucial roles in various pathological and physiological processes. The development of optical probes for biothiols has been an active research area in recent years. Herein, a new turn-on fluorescence probe (HD-NBD) was designed and synthesized by fusing tetrahydro[5]helicene and 7-nitro-2,1,3-benzoxadiazole (NBD) for simultaneous discrimination of Hcy/Cys, H2S and GSH in aqueous solution. This probe is able to show unique absorbance enhancement at 548 nm for H2S and additional fluorescence enhancement at 536 nm only for Cys/Hcy, which can be used to discriminate H2S, Cys/Hcy and GSH simultaneously. In addition, HD-NBD also shows low background without any self-fluorescence, as well as high selectivity toward common biothiols. The low detection limits of this probe are about 0.15 μM for Hcy with a wide linear range (1-80 μM), 0.36 μM for Cys (linear range: 1-45 μM), 0.79 μM for H2S (linear range: 1-80 μM) and 4.44 μM for GSH (linear range: 1-60 μM). Moreover, HD-NBD can identify Hcy/Cys, H2S from GSH and other amino acids with high sensitivity and selectivity, therefore it could be used for detecting endogenous and exogenous Hcy/Cys under biological condition.