Advances in Fingerprint Technology.pdf

Figure 5.14 The red pigment formed by the reaction of DFO with amino acids
(XXIII). Notice the resemblance to Ruhemann’s purple (XII). (From Grigg, R.,
Mongkolaussavaratana, T., Pounds, C.A., and Sivagnanam, S., 1,8-Diazafluorenone
and related compounds. A new reagent for the detection of alpha amino acids and
latent fingerprints, Tetrahedron Lett., 31, 7215, 1990.)
Latent fingerprints that were treated with DFO displayed only a faint red
color but they luminesced brightly under green light (absorption maximum
at about 470 nm and emission maximum at about 570 nm 136 ). There was no
need for a secondary treatment with metal salt to induce luminescence, and
the total number of identifiable prints developed by it was considerably
higher than with ninhydrin. These properties very quickly made DFO the
most important fluorogenic reagent for latent fingerprints. The best formulation
still uses Fluorisol as the main carrier solvent, but a thorough study
has been initiated to find an acceptable alternative. 137 The formulation proposed
by the PSDB is a 0.025% solution of DFO in Fluorisol containing 3%
methanol and 2% acetic acid. Optimal development conditions are 20 min
at 100°C and no humidity. 55 Stoilovic’s modification also included chloroform
in the mixture, and the final concentration of DFO was 0.04%. 138 A
non-CFC formulation based on petrol ether as the main carrier was suggested
by Margot and Lennard. 139 Its main disadvantage is high flammability.
Another non-CFC formulation, based on tert-butylmethyl ether, was suggested
by Geide. 140 Conn, Lennard, and co-workers found that secondary
treatment with metal salts had only a negligible effect on the luminescence
although metal complexes had been formed. 141
Several attempts to obtain an improved DFO reagent by modifying its
molecule (DFO analogues) were unsuccessful. 134 There has been no followup
to the observation of Frank and Handlin in 1993 142 that two compounds
structurally related to DFO, one of them dipyridyl ketone, produce very
strong fluorescence when reacted with amino acids. On the other hand, some
ketals derived from DFO to increase its solubility in nonpolar solvents do
react with latent fingerprints but not as well as DFO. 143
At present, DFO is considered the best fluorogenic fingerprint reagent
for paper and porous surfaces, and it is used as the first stage of the chemical
sequence: DFO, ninhydrin, and PD.