DAPI
Definition
4',6-diamidino-2-phenylindole; a fluorescent dye that binds double-stranded DNA and emits blue (~460 nm) under UV excitation (~360 nm). Standard nuclear counterstain; used in forensic sperm-head identification to identify nucleated cells.
- Full name
- 4',6-diamidino-2-phenylindole
- Binds
- Double-stranded DNA
- Excitation/emission
- ~360 nm UV excitation, ~460 nm blue emission
- Forensic use
- Sperm-head identification via nuclear staining
Common questions
Why is DAPI specifically useful for locating sperm heads on a slide rather than just any cell?+
DAPI stains all nucleated cells, but sperm heads have a distinctively condensed, compact nuclear morphology under fluorescence that is visually different from the larger, more diffuse nuclei of epithelial or white blood cells, so an examiner can distinguish sperm heads from other cell types by shape as well as by staining.
What does a DAPI stain not tell the examiner about a sample?+
DAPI confirms the presence of DNA-containing cells and their morphology but provides no information about whose DNA is present or in what quantity suitable for profiling; it is a locating and screening tool used before DNA extraction and STR typing, not a substitute for them.
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