Reversible, zinc-selective chemical reactions that enable imaging biological Zn2+ at long wavelengths

Fluorescent sensors are valuable tools for investigating the biochem. of metal cations, notably calcium and zinc. Most probes rely on quenching of photoinduced electron transfer as a fluorescence turn-on mechanism. The information that can be obtained from this kind of probe is limited by their sensitivity to pH and inability to operate effectively at longer wavelengths, esp. \textgreater700 nm, which facilitates deep tissue penetration. Here we describe a new family of fluorescent sensors that take advantage of zinc-induced, reversible, ring-opening reactions, that elicit a strong fluorescence turn-on response. These reactions (Scheme 1) occur rapidly (t1/2 ∼ 3 s) and selectively (Zn2+ \textgreater\textgreater Mg2+, Ca2+, K+, Na+) in cuvettes under physiol. conditions and in live cells. The pH insensitivity of some of these probes and their emission wavelength in the NIR-region are prominent advantages over existing fluorescent sensors for imaging biol. mobile zinc. This work was supported by a grant from the National Institutes of Health and a fellowship to P. From the Swiss National Science Foundation.