A Mitochondrial-Targeted Two-Photon Probe for Zinc Ion

We report a two-photon probe (SZn-Mito) for mitochondrial zinc ions ([Zn2+](m)). This probe shows a 7-fold enhancement of two-photon-excited fluorescence in response to Zn2+ with a dissociation constant (K-d(TP)) of 3.1 +/- 0.1 nM and pH insensitivity in the biologically relevant range, allowing the detection of [Zn2+](m) in a rat hippocampal slice at a depth of 100-200 mu m without interference from other metal ions through the use of two-photon microscopy.