The development of a biotin-guided and mitochondria-targeting fluorescent probe for detecting SO2 precisely in cancer cells

Mitochondrial sulfur dioxide (SO₂) is very closely associated with various activities of cancer cell. However, the specific physiological and pathological roles of mitochondrial SO₂ in cancer cells are still not well defined. Lacking a powerful molecular tool for detecting mitochondrial SO₂ in cancer cells precisely is an essential factor. So it is urgent to develop a specific method for monitoring mitochondrial SO₂ in cancer cells. Herein, we described a distinct cancer cell-specific fluorescent probe NS for detecting mitochondrial SO₂ accurately in cancer cells. Biotin, possessing of high affinity for cancer cells, was decorated into probe to provide its cancer cell-targeting property. Moreover, the positive charge hemicyanine group was used to anchor mitochondria selectively. A series of spectral results from concentration titration, dynamics and selectivity experiments showed that NS had high sensitivity, fast response and high selectivity to SO₂. These properties render NS ability for detecting SO₂ in living cells. In biological imaging, the achievements in detecting exogenous and endogenous SO₂ displayed the probe had favorable response to SO₂ in living cells with well biocompatibility. Significantly, assisted by competitive experiments with excess biotin, NS demonstrated distinct cancer cell-targeting for detecting mitochondrial SO₂. Furthermore, NS could locate mitochondria specially and detect mitochondrial SO₂ in cancer cells by co-localization. Moreover, NS can trace SO₂ in zebrafish with long wavelength emission. Therefore, NS can achieve in tracing mitochondrial SO₂ selectively in cancer cells. It would be a powerful tool for well defining the physiological and pathological roles of mitochondrial SO₂ in cancer cells.