Far-Red BODIPY-Based Fluorescent Probe for the Selective Detection of Cysteine and Hydrogen Sulfide: Applications in Blood Serum Analysis and Live-Cell Imaging

Cysteine (Cys) is a crucial biomolecule involved in protein synthesis, antioxidant defense, and cellular signaling, while H<inf>2</inf>S serves as a gasotransmitter. The imbalance of these thiols is linked to a range of pathological conditions, highlighting the need for precise and reliable detection methods. Herein, we have developed a bright far-red fluorescent probe (BYN-DNS) for the selective and sensitive detection of Cys and H<inf>2</inf>S. The probe is synthesized using methoxy-1-naphthaldehyde modified BODIPY molecule (BYN-OH) functionalized with a 2,4-dinitrobenzene sulfonyl (DNS) moiety. The probe produces very low fluorescence due to ICT between the DNS group and the BYN-OH derivative. In the presence of Cys and H<inf>2</inf>S, the DNS group cleaved by nucleophilic substitution reaction, releasing the far-red fluorophore BYN-OH and resulting in an 81- and 122 fold increase in fluorescence at 610 nm, respectively. The probe exhibits significant selectivity for Cys and H<inf>2</inf>S compared to structurally similar thiol, including homocysteine (Hcy) and glutathione (GSH). The detection limits were calculated to be 85 nM for Cys and 68 nM for H<inf>2</inf>S. The quantum yield of the probe in the presence of H<inf>2</inf>S was calculated to be 0.63. The practical applicability and biocompatibility of BYN-DNS were confirmed via human blood serum analysis and live-cell fluorescence imaging.