Molecular engineering of a mitochondrial-targeting two-photon in and near-infrared out fluorescent probe for gaseous signal molecules H₂S in deep tissue bioimaging

Hydrogen sulfide (H₂S), one of the biologically important gaseous signal molecules, plays an essential role in diverse normal biochemical functions and pathological processes. Herein, an efficient two-photon in and near-infrared out mitochondria-targeting dye has been designed, synthesized and characterized. It is easily synthesized by the condensation reaction (C˭C) of 4-hydroxybenzaldehyde and 6-(diethylamino)−1,2,3,4-tetrahydroxanthylium (mitochondria-targeting), which possesses large two-photon action absorption cross-section ~160 g and high fluorescence quantum yield ~0.15. Encouraged by the results, we proceeded to conjugate this new dye with a H₂S recognition moiety (4-dinitrobenzene-ether, DNB), on the basis of the intramolecular charge transfer (ICT) strategy, to construct a novel H₂S fluorescent probe (TP-NIR-HS), which shows a targeting ability with high sensitivity and selectivity, and low cytotoxicity. This new probe was then applied for two-photon imaging of living cells and tissues and showed high imaging resolution and a deep-tissue imaging depth of ~350 µm, thus demonstrating its practical application in biological systems, and providing a valuable theoretical basis and technical support for the study of physiological and pathological functions of H₂S.