A novel two-photon fluorescence probe for Zn(2+) derived from dicyanostilbene as a two-photon fluorophore and 4-(pyridine-2-ylmethyl)piperazine as a novel Zn(2+) ligand was developed. The probe shows a 72.5-fold fluorescence enhancement in response to Zn(2+), a large two-photon action cross-section (580 GM), a noncytotoxic effect, and pH insensitivity in the biologically relevant range, and its dissociation constant (K(d)(TP)) is 0.52 ± 0.01 μM. The probe can selectively detect free Zn(2+) ions in live cells for 1500 s or so and in living tissues at a depth of 80-150 μm without interference from other metal ions and the membrane-bound probes.

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