Zinc(II) ions are active components in enzymes and proteins. For proper brain function, it is vital to maintain zinc ion homeostasis, which is controlled by the import and export of intracellular zinc ions to and from extracellular space and specific organelles, such as the endoplasmic reticulum and mitochondria. To understand its role in biology, it is crucial to monitor zinc ion activity in different cellular compartments.
Bong Rae Cho and co-workers at Korea University, Seoul, have developed a two-photon probe that can detect zinc ions near the plasma membrane. The probe is based on a combination of a fluorine-derived fluorophore and an aniline-based zinc chelator, and is lipophilic, hence its affinity for the cell membrane. When a zinc ion binds to the chelator, it blocks photoinduced electron transfer within the probe and this results in enhanced fluorescence.
The probe is highly selective for zinc ions with a dissociation constant of 20 nM, a fluorescence enhancement factor of 5, and a two-photon action cross section of 43 GM in the presence of excess zinc ions. It can easily be loaded into cells and tissue slices, and visualizes near-membrane zinc ions in live cells and tissues for hundreds of seconds through the use of two-photon microscopy.