High-selective two-site fluorescent probe for Cys/SO₂ detection and cell imaging

A fluorescent probe has been designed using cyanine phenothiazine and 7-nitro-1,2,3-benzoxadiazole (NBD) for selective detection of Cys-SO₂ components. The probe utilizes the NBD structure to achieve specificity towards Cys and employs a reaction mechanism between the double bond of cyanine and phenothiazine with SO₃^2- to achieve selectivity towards SO₂. Importantly, the NBPI phenothiazine structure incorporates a large C-O bond energy attached to NBD, effectively eliminating interference from Hcy and ensuring highly selective response to Cys. The optimized design of the probe enables excellent linearity and extremely low detection limits for Cys-SO₂ components in vitro experiments. The probe NBPI allows separate detection of Cys-SO₂ in the presence of both components. Furthermore, the probe NBPI demonstrated successful imaging of endogenous and exogenous Cys and SO₂ in cell studies.