Acridine orange (AO) solution is used as nuclear dye. AO forms a complex with double-stranded DNA to emit green fluorescence, AO also forms a complex with singlestranded DNA or RNA to emit red fluorescence. One molecule of AO intercalates with three base pairs of double-stranded DNA and emits green fluorescence with the maximum wavelength at 526 nm (excitation 502 nm). One molecule of AO can also interact with one phosphate group of single-stranded DNA or RNA to form an aggregated, or stacked, structure that emits red fluorescence with the maximum wavelength at 650 nm (excitation 460 nm)