"The development of GZnP3 has filled such a gap for the scientific community giving an unprecedented ability to study cellular Zn²⁺ dynamics with sub-nanomolar sensitivity in real time. GZnP3 binds labile Zn²⁺ with a Kd of 1.3 nM, giving it the ability to detect this metal ion in the sub-nanomolar range. Though other genetically encoded Zn²⁺ probes have similar binding affinities (Table 1), GZnP3 has approximately an 11-fold dynamic range from its apo state to Zn²⁺ saturation (17-fold in vitro), making it the most sensitive protein-based Zn²⁺ sensor currently available for monitoring sub-nanomolar cellular Zn²⁺ dynamics, between 100 pM and 1 nM. It has high specificity for Zn²⁺ over a range of other biologically relevant cations, including Ca²⁺ and Fe²⁺. Together, these characteristics permit the use of GZnP3 to observe minute changes in cytosolic [Zn²⁺] from the high picomolar to low nanomolar range. Though it is a powerful tool, it does have limitations for its use in the dynamic cellular environment. Primarily, like many GFP-based fluorophores, we are aware of its sensitivity to changes in pH. To account for this, however, we have established a normalization method to obtain pH-corrected GZnP3 signals by simultaneously recording GZnP3 (Zn²⁺) and pHuji (pH) signals (Supplementary Fig. 5)."