Fluo-4, pentaammonium salt is widely used in biological research as a fluorescent calcium indicator. It is particularly valuable in live-cell imaging to measure intracellular calcium levels. When bound to calcium ions, Fluo-4 exhibits a significant increase in fluorescence intensity, allowing researchers to monitor calcium dynamics in real-time. This application is crucial in studying cellular processes such as signal transduction, muscle contraction, and neurotransmitter release. Its high sensitivity and low photobleaching make it a preferred choice for fluorescence microscopy and flow cytometry experiments. Additionally, Fluo-4 is often employed in drug discovery to assess the effects of compounds on calcium signaling pathways.