How does ethidium bromide work?

Ethidium bromide is a planar molecule with a ring structure that resembles the rings of DNA bases. It is also hydrophobic, fluorescent and visible under UV light.

The flat structure made of ethidium bromide makes it easy for the molecule to intercalate or insert itself between adjacent base pairs in the DNA double helix. This interaction alters the structure of DNA, distorting its weight, conformation, charge, and flexibility, and slightly unwinding the helix.

On binding with DNA, ethidium bromides experience a 20 – 25 fold in brightness. When exposed to UV light, it fluoresces with an orange color, facilitating the detection of DNA in agarose gel electrophoresis experiments.