Fluo-3, pentapotassium salt, is widely used as a fluorescent calcium indicator in biological research. It is particularly valuable in studying intracellular calcium dynamics in live cells. When bound to calcium ions, it exhibits a significant increase in fluorescence intensity, allowing researchers to visualize and quantify calcium concentration changes in real-time. This makes it a crucial tool in neuroscience, cardiology, and cell biology for understanding calcium signaling pathways, cellular responses to stimuli, and the role of calcium in various physiological and pathological processes. Its cell-permeant nature and high sensitivity make it suitable for applications such as fluorescence microscopy, flow cytometry, and fluorescence plate reader assays.