ZnAF-2, 6-iso-, is a cell-impermeable compound that acts as a high-affinity Zn²⁺-specific fluorescent probe (Kd = 2.7 nM). It shows low basal fluorescence and the fluorescence intensity increases ~51-fold upon stoichiometric (1:1) binding to Zn²⁺. Exhibits little affinity towards Ca²⁺, Mg²⁺, Na⁺, or K⁺.