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 high sensitivity and large fluorescence enhancement upon binding make it suitable for applications such as fluorescence microscopy, flow cytometry, and fluorescence plate reader assays. Note that the pentapotassium salt form is typically used after intracellular loading via the cell-permeant AM ester.