Studies have found that iron is the most abundant transition metal element in living organisms and is involved in a variety of physiological activities. In recent years, free iron ions in cells have received more and more attention due to their high reactivity and certain association with cell damage and death. Intracellular free iron ions exist in stable Fe2+ and Fe3+ forms. In terms of the reducing environment, metal transporters and water solubility of Fe2+, Fe2+ is more important than Fe3+. This kit provides a fluorescent probe that can specifically bind to Fe2+, which can enter the cell well and is suitable for the detection of Fe2+ in live cells. When the probe reacts with Fe2+, an irreversible orange-red fluorescent product (excitation: 542 nm, emission wavelength: 575 nm) is generated.