7-Amino-actinomycin D

7-Amino-actinomycin D (also 7-aminoactinomycin D, abbreviated 7-AAD) is a fluorescent chemical compound with a strong affinity for DNA. It is used as a fluorescent marker for DNA in fluorescence microscopy and flow cytometry. It intercalates in double-stranded DNA, with a high affinity for GC-rich regions.

Applications
With an absorption maximum at 546 nm, 7-AAD is efficiently excited using a 543 nm helium-neon laser; it can also be excited with somewhat lower efficiency using th 488 nm or 514 nm argon laser lines. Its emission has a very large Stokes shift with a maximum in the deep red: 647 nm. 7-AAD is therefore compatible with most blue and green fluorophores – and even many red fluorophones – in multicolour applications.

7-AAD does not readily pass through intact cell membranes; if it is to be used as a stain for imaging DNA fluorescence, the cell membrane must be permeabilized or disrupted. 7-AAD is also used as a cell viability stain. Cells with compromised membranes will stain with 7-AAD, while live cells with intact cell membranes will remain dark.

Actinomycin D
The related compound Actinomycin D is nonfluorescent, but binds DNA in the same way as 7-AAD. Its absorbance changes when bound to DNA, and it can be used as a stain in conventional transmission microscopy.