Superoxide anion (O₂^•–), as the precursor of other reactive oxygen species (ROS), is significantly important in the maintenance of redox homeostasis and various cellular signaling pathways. Here we present a ratiometric mitochondria-accessing fluorescent probe (NA-T) based on nucleophilic substitution mechanism for real-time measuring O₂^•–. By regulating the intramolecular charge of 1,8-naphthalimide, a ratiometric response model was obtained, which evinced 18-fold enhancement of fluorescence ratio (I_540 nm/I_475 nm) in the presence of O₂^•– over other ROS with rapid response (132 s), high sensitivity (DL = 0.370 μM) and selectivity. Confocal fluorescence images demonstrated that the probe could well permeate through plasma membrane for visualizing endogenous O₂^•– changes in mitochondria of living cells and in inflammatory Daphnia magna, indicating NA-T a potential tool for the diagnosis and research of corresponding diseases.

中文翻译：

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线粒体访问比例荧光探针成像活细胞和大型蚤中的内源性超氧阴离子

作为其他活性氧（ROS）的前体，超氧阴离子（O ₂ ^•–）在维持氧化还原稳态和各种细胞信号通路中非常重要。在这里，我们提出了一种基于亲核取代机制的比例线粒体访问荧光探针（NA-T），用于实时测量O ₂ ^•–。通过调节1,8-萘二甲酰亚胺的分子内电荷，获得了比例响应模型，该模型表明在存在O ₂ ^•的情况下荧光比（I _{540 nm} / I _{475 nm}）提高了18倍^。与其他ROS相比，具有快速响应（132 s），高灵敏度（DL = 0.370μM）和选择性。共聚焦荧光图像表明，该探针可以很好地穿透质膜，以观察活细胞线粒体和炎性水蚤中内源性O ₂ ^•–的变化，表明NA-T是诊断和研究相应疾病的潜在工具。