Two-photon probes for Zn2+ ions with various dissociation constants. Detection of Zn2+ ions in live cells and tissues by two-photon microscopy.

A series of Zn(2+)-selective two-photon fluorescent probes (AZnM1-AZnN) that had a wide range of dissociation constants (K(d) (TP) =8 nm-12 μM) were synthesized. These probes showed appreciable water solubility (>3 μM), cell permeability, high photostability, pH insensitivity at pH>7, significant two-photon action cross-sections (86-110 GM) upon complexation with Zn(2+), and can detect the Zn(2+) ions in HeLa cells and in living tissue slices of rat hippocampal at a depth of >80 μm without mistargeting and photobleaching problems. These probes can potentially find application in the detection of various amounts of Zn(2+) ions in live cells and intact tissues.