Dactolygraphic Facilitating Operations

A modern alternative and/or complement to ninhydrin is 1,8-diazafluoren-9-one (DFO) which is reported to be more sensitive than ninhydrin and gives a fluorescent product as well. After two molecules of DFO react with an amino acid residue in latent fingerprints, the highly conjugated Ruhemann’s Purple-type product is red or pink colored. This substance also shows excitation at approximately 470 nm with a green-yellow fluorescent emission at 560 nm. Besides enhanced sensitivity, the advantage of having a fluorescent print is that it can be distinguished from a colored and/or printed background. Interestingly, this new reagent was introduced in a 1990 article in a chemistry journal, Tetrahedron Letters with the title “1,8-Diazafluoren-9-one and related compounds. A new reagent for the detection of alpha-amino acids and latent fingerprints.” The mechanism shown below was published in 2000, “Study of the reaction mechanism of 1,8-diazafluoren-9-one with the amino acid, L-alanine.” DFO is only slightly soluble in methanol. One formulation proposed in the literature starts with a stock solution of 1 gram of DFO dissolved in 62.5 mL chloroform, 125 mL methanol, and 12.5 mL acetic acid. A 80 mL portion of this stock solution is diluted to 1000 mL with 1,1,2-trichlorotrifluoroethane before use. The final concentration of DFO is thus 0.4 mg/mL.

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