Red-emitting fluorescent probe with excellent water solubility for the in situ monitoring of endogenous H₂S in wheat under salt and Al³⁺ stress

Hydrogen sulfide (H₂S) is a pivotal signaling molecule in plants and appropriate levels are essential for normal growth. As such the real-time detection of H₂S in plants is required since it enables timely targeted interventions. However, most fluorescent probes for detecting H₂S reported to date exhibit fluorescence quenching in aqueous solution thereby significantly constraining their potential for in vivo applications. In response to this challenge, we present a natural flavylium-inspired fluorescent probe with robust water solubility for turn-on detection of H₂S in organisms. The probe exhibits a remarkable 28-fold turn-on signal at 619 nm with rapid reaction kinetics (−20 min), coupled with high sensitivity (LOD = 0.37 μM) and exceptional selectivity for H₂S. By employing the probe as an imaging agent, we managed to successfully visualize the fluctuations of exogenous and endogenous H₂S levels in HeLa cells. More importantly, the probe enabled the facile and precise visualization of H₂S in stressed wheat roots, achieving remarkable micron-level resolution through in-situ imaging, thereby confirming the upregulation of H₂S in response to aluminum ion and salt stress. Our research provides a novel tool to investigate the response and mitigation mechanisms of H₂S in plants under diverse stress conditions, as well as strategies for enhancing crop resilience.