An ultra-rapid response NIR fluorescent probe for in vivo tracking of sulfite dynamic changes

The sulfur oxidation axis is a core component of the body's sulfur metabolic network, governing the directional interconversion of sulfur species and maintaining metabolic homeostasis. Disruption of this axis can result in the accumulation of toxic intermediates or impaired biosynthetic disorders, both of which are implicated in a range of various diseases. As a central hub in sulfur metabolism, sulfite represents a critically metabolic junction linking upstream reduced sulfur species to downstream oxidized products. However, traditional analytical approaches rely on tissue homogenization, precluding the resolution of sulfite dynamics in vivo spatiotemporal precision. Although fluorescent probes for sulfite detection have been reported, most suffer from limitations in response speed, emission wavelength or biological applicability. To overcome these challenges, we developed three sulfite-responsive fluorescent probes-PNS, QNS and DNS, and systematically evaluated their performance. Among them, DNS emerged as the optimal candidate, exhibiting an ultra-rapid response time (< 2 s) in aqueous media, near-infrared emission at 700 nm for enhanced tissue penetration and excellent selectivity and biocompatibility. Using DNS, we demonstrated in living HepG2 cells that cysteine (Cys) serves as a precursor for sulfite, which is subsequently oxidized to sulfate. Notably, leveraging the superior photophysical properties of DNS, we achieved rapid dynamic tracking of sulfites in a living mouse model. Collectively, this work establishes essential technical support for in vivo sulfite visualization and provides critical technical support for elucidating the physiological functions of sulfite and the pathological mechanisms associated with dysregulated sulfur metabolism.