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DFO as a Fingerprint Development Reagent

DFO as a Fingerprint Development Reagent May 23, 2022 - BY RealScan Biometrics

DFO as a Fingerprint Development Reagent

The interaction of 1,8-diazafluoren-9-one (DFO) with amino acids was not investigated until 1990, when it was first used as a fingerprint development reagent.
DFO treatment resulted in faint red or pink fingerprints that were strongly fluorescent at room temperature, according to preliminary findings.
DFO was quickly selected as the best fluorescent reagent for fingerprint production, surpassing the metal complexation-induced fluorescence of ninhydrin-developed fingerprints.
The reagent is currently commonly used to generate fingerprints on porous surfaces in conjunction with ninhydrin. 


DFO Reagent in Forensic Science

DFO is not a direct analogue of ninhydrin, but the compounds' structures and the results of their interactions with amino acids are very similar.
DFO, like ninhydrin, has a core ketone centre that is activated by the presence of electron-withdrawing groups nearby.
The structure of DFO; the nitrogenous rings function similarly to the flanking ketone groups in ninhydrin. The presence of methanol is required for DFO's interaction with amino acids, according to mechanistic studies.
This allows the DFO to form a hemiketal, which is less stable than the parent structure and hence more reactive, resulting in a more sensitive fingerprint response to amino acid residues.
The red-colored byproduct of the reaction has been completely defined and is similar to Ruhemann's purple.
The reaction's byproduct is pink to red in hue, with a maximum absorption wavelength of roughly 560 nm and a lesser absorption wavelength of 520 nm.
The product is extremely fluorescent at room temperature when excited by either of these wavelengths, emitting bright light of 576 nm. 
The DFO reaction, unlike the ninhydrin reaction, necessitates a high-temperature, low-humidity environment.
The intensity of the DFO product's fluorescence is unaffected by post-treatment with metal salts and subsequent cooling to liquid nitrogen temperatures.
DFO is said to be a more sensitive fingerprint development reagent than ninhydrin, yielding more discernible latent fingerprints.
Because a weakly fluorescing fingerprint is easier to see than a weakly colored fingerprint, this sensitivity prevails.
Despite this, using ninhydrin following DFO treatment promotes further development, resulting in Ruhemann's purple.
The standard explanation for this phenomenon is that, while DFO-developed fingerprints fluoresce more brightly, DFO does not completely react with every amino acid in the fingerprint residue, leaving some amino acids available for ninhydrin to react with.
DFO followed by ninhydrin produces more latent fingerprints than either DFO or ninhydrin alone, and thus is the suggested testing sequence for porous materials like paper.


DFO Applications in Forensic Laboratories

There have been several DFO formulations published in the literature.

DFO solution can be applied to specimens by dipping, spraying, or brushing, but dipping is preferred.

To promote development, the exhibit is allowed to dry before being heated. Heating in a 100°C oven for 10–20 minutes, using a 160°C iron for 20–30 seconds, or using a 180°C ironing press for 10 seconds are all viable options.

Because moisture interferes with the development process, the reaction must be carried out in a dry, low-humidity environment.

Using 530 nm excitation light and a 590 nm barrier filter, or 555 nm excitation light and a 610 nm barrier filter, developed fingerprints can be observed after DFO application and heating. After that, the exhibit can be treated with ninhydrin as discussed above.

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