A Three-Photon Active Organic Fluorophore for Deep Tissue Ratiometric Imaging of Intracellular Divalent Zinc

Abstract

Deep tissue bioimaging with three-photon (3P) excitation using near-infrared (NIR) light in the second IR window (1.0–1.4 μm) could provide high resolution images with an improved signal-to-noise ratio. Herein, we report a photostable and nontoxic 3P excitable donor-π-acceptor system (GMP) having 3P cross-section (σ3) of 1.78×10−80 cm6 s2 photon−2 and action cross-section (σ3η3) of 2.31×10−81 cm6 s2 photon−2, which provides ratiometric fluorescence response with divalent zinc ions in aqueous conditions. The probe signals the Zn2+ binding at 530 and 600 nm, respectively, upon 1150 nm excitation with enhanced σ3 of 1.85×10−80 cm6 s2 photon−2 and σ3η3 of 3.33×10−81 cm6 s2 photon−2. The application of this probe is demonstrated for ratiometric 3P imaging of Zn2+ in vitro using HuH-7 cell lines. Furthermore, the Zn2+ concentration in rat hippocampal slices was imaged at 1150 nm excitation after incubation with GMP, illustrating its potential as a 3P ratiometric probe for deep tissue Zn2+ ion imaging.