9-Amino-6-chloro-2-methoxyacridine (ACMA) is a cell-permeable fluorescent probe that intercalates into DNA. It selectively binds to poly(dA-dT) sequences with the fluorescence lifetime decreasing with incorporation of guanosine. It is used for labeling DNA and displays excitation/emission spectra of 411/475 nm, respectively. ACMA fluorescence is pH-dependent and is quenched when a pH gradient is established, a property that has been utilized in animal- and plant-based studies. It also inhibits acetylcholinesterase with a Ki value of 49 nM.