A luminescent probe is a substance whose substrate moves to an excited state through chemical reactions and then returns to a ground state, emitting light. Thanks to the use of chemical reactions, luminescent probe is characterized by a high selectivity, which contributes to low background noise and increases signal detection. Since a luminescent probe covers a wide dynamic range, it is often used to investigate the dynamics of ATP and calcium ions. It is also used as a reporter gene to visualize specific cells or investigate gene expression. FUJIFILM Wako sells AkaLumine-HCl and coelenterazine, which perform better than the substrates used in conventional luminescent probes.