Porphyrinic Probe for Fluorescence “Turn-On” Monitoring of Cu+ in Aqueous Buffer and Mitochondria

A zinc(II) porphyrin derivative (ZPSN) was designed and synthesized, and this probe exhibited rapid, selective and reversible binding to Cu+ for fluorescence monitoring in pure aqueous buffer. The detection mechanism is based on Cu+-activated disruption of axial coordination between the pyridyl ligand and the zinc center, which changes the molecular geometry and inhibits intramolecular electron transfer (ET), leading to fluorescence enhancement of the probe. The proposed sensing mechanism was supported by UV–vis spectroscopy/fluorescence spectral titration, NMR spectroscopy, mass spectrometry, and time-resolved fluorescence decay studies. The dissociation constant was calculated to be 6.53 × 10–11 M. CLSM analysis strongly suggested that ZPSN could penetrate live cells and successfully visualize Cu+ in mitochondria. This strategy may establish a design and offer a potential building block for construction of other metal sensors based on a similar mechanism.