Anionic heptamethine cyanine as reactive sulfur species-activated probe: Application of NIR-II fluorescence imaging for in vivo visualization of glutathione

Understanding glutathione (GSH)-related pathophysiological mechanisms requires their effective visualization. Current fluorescence probes for GSH visualization that operate in the visible and near-infrared (NIR-I) windows suffer from limited penetration in tissue and significant tissue autofluorescence. As part of this study, a GSH-activatable second near-infrared (NIR-II) fluorescent probe (denoted as T2S2) was developed to visualize GSH in vivo in a highly sensitive and selective manner. T2S2 contains an anionic polymethylcyanide framework coupled to a 3,4-dimethoxybenzenethiol fluorescence quenching moiety specifically activated by GSH. In response to this activation, the NIR-II fluorescence is significantly enhanced, enabling the effective discrimination of GSH from similar biothiols with low molecular weight. The GSH detection limit of T2S2 was established to be 90 nM, accompanied by a color change from blue-green to yellow-green. Notably, the T2S2 probe was found to be highly selective and sensitive to GSH in vivo. Hence, this study presents a promising approach for developing activatable NIR-II fluorescent probes to image GSH and other biomarkers in vivo.