Calbryte™-520XL, AM is a new fluorescent and cell-permeable calcium indicator with extremely low affinity. Like other dye AM cell loading, Calbryte™-520XL AM ester is non-fluorescent, and once it gets inside the cell, it is hydrolyzed by intracellular esterase and gets activated. The activated indicator is a polar molecule that can no longer freely diffuse through the cell membrane, essentially trapped inside cells. Calbryte™-520XL has a low affinity for calcium ions with a Kd ~300 uM, similar to the well-known Rhod 5N, but it is much more stable. Calbryte™-520XL produces a bright fluorescence signal in the presence of calcium ions in high concentration. It has an excitation and emission wavelength identical to Fluo-4. Thus, the same Fluo-4 assay settings can be readily applied to Calbryte™-520XL-based calcium assays. Calbryte™-520XL is an excellent alternative to Rhod-5N. We also offer Calbryte™-520XL, potassium salt (#20645), Calbryte™-520XL-dextran (#20648), Calbryte™-520XL azide (#20643) that can be readily conjugated to a carrier through the well-known click chemistry.