Fluo-3 potassium 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 Fluo-3 binds to calcium ions, its fluorescence intensity increases significantly, allowing researchers to visualize and quantify calcium fluctuations in real-time. This application is crucial in fields such as neuroscience, cardiology, and cell biology, where calcium signaling plays a pivotal role in cellular processes like muscle contraction, neurotransmitter release, and cell proliferation. Fluo-3 is often loaded into cells in its ester form, which is then hydrolyzed intracellularly to the active form. Its high sensitivity and specificity for calcium make it a preferred tool for imaging calcium transients in single cells or tissues using fluorescence microscopy or flow cytometry.