5-Nitro BAPTA tetramethyl ester, a calcium chelator, is involved in the synthesis of two-photon probes and is used for real-time imaging of intracellular calcium ions and monitoring calcium waves at depths of 100-300 μm in liver tissues for 1100-4000 s. Additionally, in conjunction with fluorescent compound 2-Me-substituted TM, it can form a red fluorescent probe (CaTM-2 AM) [1] [2].