A near-infrared fluorescent probe for ratiometric sensing of SO₂in cells and zebrafish

Developing suitable molecular tools for monitoring SO2 and its derivatives in living organisms is attractive due to their importance for human health. Herein, the first near-infrared fluorescent probe Mito-HN with aggregation-induced emission enhancement (AIEE) characteristics for ratiometric sensing of SO2 derivatives in vitro, in cells, and in zebrafish was designed and synthesized. By connecting the electron-donating naphthopyran and electron-withdrawing hemicyanine via the alkenyl group, this probe displays a near-infrared fluorescence emission and notable solid-state luminescence with AIEE features. Based on the specific 1,4-addition reaction of HSO3-/SO32- with the CC double bond of Mito-HN, this probe can specifically sense HSO3- in real time with an excellent near-infrared ratiometric fluorescence effect, a low detection limit of 0.17 μM, and a fast response time of less than 30 s. Cell imaging and zebrafish imaging results demonstrate that Mito-HN can ratiometrically not only sense endogenous SO2 derivatives in mitochondria but also monitor SO2 in living organisms. We anticipate that Mito-HN could be applied for the diagnosis of SO2-related diseases in the future.