Fluo-4, pentasodium salt is widely used in biological research as a fluorescent calcium indicator. It is particularly valuable in live-cell imaging studies to monitor intracellular calcium levels with high sensitivity. When bound to calcium ions, Fluo-4 exhibits a significant increase in fluorescence intensity, allowing researchers to visualize and quantify calcium dynamics in real-time. This makes it a crucial tool in studying cellular processes such as signal transduction, muscle contraction, and neuronal activity. Its high water solubility further enhances its utility in various experimental setups, including fluorescence microscopy and flow cytometry. Additionally, Fluo-4 is often employed in drug discovery to assess the effects of compounds on calcium signaling pathways.