A Novel, Cell-Permeable, Fluorescent Probe for Ratiometric Imaging of Zinc Ion

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Abstract
Zn2+ plays important roles in various biological systems; as a result, the development of tools that can visualize chelatable Zn2+ has attracted much attention recently. We report here newly synthesized fluorescent sensors for Zn2+, ZnAF-Rs, whose excitation maximum is shifted by Zn2+ under physiological conditions. Thus, these sensors enable ratiometric imaging, which is a technique to reduce artifacts by minimizing the influence of extraneous factors on the fluorescence of a probe. Ratiometric measurement can provide precise data, and some probes allow quantitative detection. ZnAF-Rs are the first ratiometric fluorescent sensors for Zn2+ that enable quantitative analysis under physiological conditions. ZnAF-Rs also possess suitable Kd for applications, and high selectivity against other biologically relevant cations, especially Ca2+. Using these probes, changes of intracellular Zn2+ concentration in cultured cells were monitored successfully. We believe that these probes will be extremely useful in studies on the biological functions of Zn2+.