Dicyanostilbene-Derived Two-Photon Fluorescence Probe for Free Zinc Ions in Live Cells and Tissues with a Large Two-Photon Action Cross Section

A novel two-photon fluorescence probe for Zn2+ derived from dicyanostilbene as a two-photon fluorophore and 4-(pyridine-2-ylmethyl)piperazine as a novel Zn2+ ligand was developed. The probe shows a 72.5-fold fluorescence enhancement in response to Zn2+, a large two-photon action cross-section (580 GM), a noncytotoxic effect, and pH insensitivity in the biologically relevant range, and its dissociation constant (KdTP) is 0.52 ± 0.01 μM. The probe can selectively detect free Zn2+ 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.