关键词: 二氧化硫, 荧光探针, 双模式响应, 分子内电荷转移, 细胞成像

SO₂ is an important gaseous signaling molecule in living organisms, and its abnormal concentration is closely associated with various physiological and pathological processes, including respiratory and central nervous system diseases. SO₂ exists mainly as HSO₃⁻ in aqueous solution, making the development of highly specific and high-contrast detection methods for HSO₃⁻ crucial for studying the physiological functions of SO₂ and the early diagnosis of related diseases. In this study, a quinoline-based near-infrared fluorescent probe, QS-EC, with an A-π-A structure was designed and synthesized. The probe initially exists in a fluorescent "dark state." Upon specific 1,4-nucleophilic addition with HSO₃⁻, its structure transforms into a D-π-A configuration, restoring the intramolecular charge transfer (ICT) effect and resulting in a dual-mode response of solution color deepening and fluorescence turn-on. The optical performance of QS-EC was systematically evaluated using UV-Vis and fluorescence spectroscopy. Spectroscopic results showed that the QS-EC responded to HSO₃^- within 3 s, with a detection limit of 14.69 nmol/L, and remains stable within a pH range of 6-13. Competitive experiments demonstrated that QS-EC exhibits high selectivity for HSO₃⁻ without interference from other anions or biothiols. It is worth emphasizing that QS-EC enables efficient detection of HSO₃⁻, which not only simplifies the detection process but also significantly enhances the probe's practicality and biocompatibility. Furthermore, MTT assays were used to evaluate its biocompatibility, revealing that cell viability remained above 80% after incubation with 0-20 μM of QS-EC for 24 hours, confirming its low cytotoxicity. For cellular imaging, QS-EC successfully enabled dynamic monitoring of both exogenous and endogenous HSO₃⁻ in live cells. Further in vivo imaging experiments in zebrafish model showed a high signal-to-noise ratio red fluorescence turn-on signal, with fluorescence intensity increasing as the HSO₃⁻ concentration rose. This indicates that QS-EC is capable of visually tracking HSO₃⁻ distribution in complex living environments. Through systematic evaluation from molecular design and spectral performance to cellular and in vivo applications, this study fully demonstrates the potential of QS-EC for early diagnosis research in SO₂-related diseases.

Key words: Sulfur dioxide, Fluorescent probe, Dual-mode, Intramolecular charge transfer, Cellular imaging