DFO (1,8-Diazafluorenone)
Definition
A chemical reagent for latent fingerprint development on porous surfaces (paper) that produces yellow-green fluorescence under 505-530 nm ALS excitation; effective on most paper types regardless of background.
- Chemical name
- 1,8-diazafluorenone
- Surface type
- Porous surfaces (paper)
- Result
- Yellow-green fluorescence
- Excitation range
- 505 to 530 nm under ALS
Common questions
Why is DFO often applied before, or instead of, ninhydrin on paper evidence?+
DFO reacts with amino acids in latent print residue to produce a fluorescent product that is detected optically under alternate light source excitation, which is generally more sensitive than ninhydrin's visible colour change and does not consume as much of the print's remaining chemistry, so it is commonly used as an earlier step in a sequential processing scheme, with ninhydrin applied afterward if needed.
Does DFO work equally well on all types of paper?+
The definition notes it is effective on most paper types regardless of background colour, since detection relies on fluorescence under ALS rather than visible contrast, which is an advantage over dye or powder methods that can be obscured on dark or patterned paper surfaces.
Related terms
- ALS (Alternate Light Source)
- An adjustable-wavelength high-intensity light source with interchangeable excitation filters, used for scene examination across UV, visible, and NIR bands; examples include the...
- Barrier Filter
- An optical long-pass filter placed over the camera lens and worn as goggles by the examiner during ALS examination; blocks the excitation...
- Hot Mirror (IR-Cut Filter)
- The infrared-blocking filter bonded in front of the digital sensor in consumer and professional cameras; must be removed or bypassed for NIR...
- Infrared Luminescence (IRL)
- A photophysical process where visible-light absorption produces NIR emission; exploited in questioned-document examination to differentiate and sequence ink strokes with different luminescent...
- Laser-Induced Fluorescence (LIF)
- Fluorescence excited by a monochromatic laser source, providing higher photon density than a broadband ALS; used for fingerprints on difficult substrates and...
- NIR (Near-Infrared)
- The spectral region from approximately 700 to 1100 nm; used in reflectance and transmittance imaging of documents, obliterated text, soot patterns under...
- Stokes Shift
- The wavelength difference between the excitation peak and the emission peak of a fluorophore. A positive Stokes shift (emission at longer wavelength...
- Time-Gated Detection
- A laser fluorescence technique that delays camera shutter opening by nanoseconds after the laser pulse to allow short-lived background fluorescence to decay...
- UV-a
- The ultraviolet band from 315 to 400 nm; the primary band used for UV-reflectance forensic imaging of bruises, GSR, and bite marks...
- UV Reflectance Imaging
- Photography using UV-A/near-UV-B incident radiation and a UV-pass, visible-blocking lens filter; reveals surface scatter differences in tissue and substrate chemistry not visible...
- Vogeley 2002 Protocol
- A UV-A reflectance photography protocol published in the Journal of Forensic Sciences (2002) demonstrating improved detection of latent bruising on dark skin...