Calcium indicator, membrane permeable. Compatible with flow cytometry, plate reader, and fluorescence microscopy assays. Excitation: 505 nm | Emission: 525 nm | Kd: 390 nM | Purity: >95% Fluo-3 is a green fluorescent, intracellular calcium (Ca²⁺) indicator with slightly red-shifted spectral properties compared to Fluo-4. Offers a large dynamic range that can be better suited for high contrast imaging applications. Is preferred over Fluo-4 for some cell types.