DFO (1,8-Diazafluoren-9-One)
Definition
A fluorescent ninhydrin analogue used for latent fingerprint development on porous surfaces; excite at 450-470 nm (with secondary absorption extending into the green up to ~530 nm), yellow-orange emission at ~565-575 nm, viewed through a yellow long-pass goggle.
- Chemical class
- Fluorescent ninhydrin analogue; reacts with alpha-amino acids
- Best surfaces
- Porous surfaces like paper, cardboard, and aged documents
- Excitation range
- 450-520 nm (blue to blue-green light), spanning two absorption peaks described in the literature
- Fluorescence color
- Yellow-orange to yellow-green (emission approximately 530-575 nm, varying by conditions)
Common questions
What does DFO do in fingerprint examination?+
DFO is a fluorescent chemical used to develop latent fingerprints on porous surfaces like paper and cardboard. It works by reacting with amino acids left in fingerprint deposits, making them glow under specialized light so they become visible and can be photographed.
How do you visualize DFO-developed fingerprints?+
You excite the DFO with blue or blue-green light (450-520 nm wavelength) and look for a yellow or yellow-green glow. Yellow long-pass goggles filter the excitation light so the examiner sees only the fingerprint fluorescence clearly.
When would you use DFO instead of ninhydrin?+
DFO is more discriminating than ninhydrin on aged or low-concentration fingerprints where ninhydrin might fail. It produces a fluorescent signal that makes it easier to photograph and document faint impressions on documents and paper evidence.
Related terms
- Alpha-Amino Acids
- Molecules bearing an amine group on the carbon adjacent to the carboxyl group; the primary molecular target of ninhydrin, DFO, and indanedione...
- Alternate Light Source (ALS)
- A device emitting light at selected wavelengths (typically 415 to 535 nm) used to detect biological fluids that fluoresce or absorb light...
- Bandpass Filter
- An optical filter transmitting a defined wavelength range (typically 20-40 nm FWHM) while blocking all others; the excitation filter in an ALS...
- Crime-Lite
- A compact, battery-powered alternate light source system (Foster+Freeman) designed for scene use by scenes-of-crime officers; the Crime-lite 82S and ML2 are standard...
- Fluorescent Whitening Agent (FWA)
- An optical brightener added to synthetic fibres and paper during manufacture; fluoresces under UV-A excitation, making treated fibres and paper highly visible...
- HFE (Hydrofluoroether)
- A class of solvents used as carriers for ninhydrin, DFO, and indanedione formulations; lower toxicity and flammability than older acetone or ethanol...
- Indanedione-Zinc
- A fluorescent amino acid reagent (indane-1,3-dione complexed with zinc chloride) that produces an orange-yellow fluorescent product; reported to be more sensitive than...
- Long-Pass (Viewing) Filter
- An optical filter transmitting all wavelengths above a defined cut-on wavelength; worn as goggles by the examiner to block excitation light while...
- Mercury Vapour Lamp
- A gas-discharge lamp producing discrete atomic emission lines, most useful at 253.7 nm (UV-C germicidal) and 365 nm (UV-A); the classic biological-fluid...
- Ninhydrin
- A chemical reagent (2,2-dihydroxyindane-1,3-dione) that reacts with alpha-amino acids in latent print residue to produce a purple-blue compound (Ruhemann's Purple); the primary...
- Physical Developer (PD)
- A multi-bath silver-deposition wet-chemistry method that deposits silver metal onto fatty latent print residue on porous surfaces; the only technique that recovers...
- Polilight
- Rofin / Omnichrome xenon-arc-based ALS platform developed in Australia; the reference platform for biological-fluid and fingerprint ALS validation studies in Australasian and...
Explained in these topics
- Chemical Methods: Ninhydrin, DFO, Indanedione and VMDA fluorescent reagent that reacts with alpha-amino acids to produce a yellow-green fluorescent imine product (excitation ~490-520 nm, emission ~530 nm); more d...
- Forensic Light Sources and Alternate Light ExaminationA fluorescent ninhydrin analogue used for latent fingerprint development on porous surfaces; excite at 450-470 nm (with secondary absorption extending into the...