Benzimidazolium-based fluorescent and colorimetric probe for selective detection of hydrogen sulfide and live-cell imaging

Background: H?S, the third most abundant endogenous gas after NO and CO, plays a key role in regulating enzymes and cellular functions. It modifies proteins, engages in metal redox reactions, and influences multiple signaling pathways, making it a significant signaling molecule in cancer biology.

Methods: Designed a benzimidazolium based dipodal moiety, selected benzimidazole scaffold as the fluorophore and introduced the active cage unit 4-azidobenzyl bromide to create a typical D-π−A structure. By adding 4-azidobenzyl bromide, electron-donating function (D) and benzimidazolium, electron-accepting function (A), remarkable fluorescence properties were achieved.

Results: H₂S plays a vital role in several physiological and pathological processes as an endogenous gas transmitter. Considering the critical importance of this active biological molecule, it is therefore extremely valuable for clarifying the complex roles of H₂S to detect it. We have designed and synthesized a benzimidazolium based dipodal donor-acceptor type H₂S selective probe. The probe exhibited a red shifted absorption peak at 530 nm and the fluorescence signal increased uniquely with the addition of H₂S. The synthesized probe shows their high selectivity and sensitivity towards H₂S. The mechanism of action of probe showed the enhanced intramolecular charge transfer process upon the treatment with H₂S, accompanied by a noticeable color change. Owing to the low cytotoxicity and enhanced fluorescence emission, the probe has been further utilized for the imaging of endogenous and exogenous H₂S in living cells.

Conclusion: Developed a novel benzimidazolium-based dipodal probe with a 4-azidobenzyl bromide unit for highly selective H?S detection. The probe exhibits a ~25-fold fluorescence increases at 410 nm upon H?S exposure, with nanomolar sensitivity. Its sensing relies on an intramolecular charge transfer mechanism and shows excellent biocompatibility and low cytotoxicity, allowing effective detection of H?S in living cancer cells.

Dr. Deepak Bains received a Ph.D in Chemistry from the Indian Institute of Technology (IIT) Ropar, India in 2021. Currently, he is working as a Postdoctoral Fellow at the Institute of Nano Science and Technology (INST), Mohali, India. His research focuses on the development of organo-inorganic biomaterials for theranostic applications, particularly composite materials designed for simultaneous imaging and treatment of solid tumors.