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Intramolecular Energy Transfer in the Europium-Ruhemann's Purple Complex: Application to Latent Fingerprint Detection

NCJ Number
Journal of Forensic Sciences Volume: 35 Issue: 1 Dated: (January 1990) Pages: 35-45
Date Published
11 pages
This paper describes a modified ninhydrin technique utilizing rare earth salts for the detection of latent fingerprints on surfaces that are not amenable to laser examination. The rare earth salts are known to form coordination compounds with Ruhemann's purple complex (RP), the reaction product of ninhydrin with amino acids found in the palmar sweat residue.
In this procedure, the RP reacts with europium chloride hexahydrate to form the organo-rare earth complex which exhibits europium luminescence at 615 nanometer with a lifetime of 0.4 milliseconds. Dye laser excitation together with absorption spectral data suggest that the fingerprint luminescence arises not only from direct excitation of the europium ion in the complex, but mainly by resonance energy transferred from the ligand to the europium ion of the complex. Experimentation with benzo(f)ninhydrin showed the luminescence of the europium complex as well as the europium emission under near-ultraviolet excitation to be more intense than that of a comparable ninhydrin complex. Because of its long-lived luminescence, the europium complex is thus suited for time-resolved imaging for eliminating short-lived or background fluorescence on porous surfaces to reveal amino acids images. 6 figures and 17 references (Author abstract modified)

Date Published: January 1, 1990