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Transcript
Latent fingermark detection using amino acid sensitive reagents Introduction The use of amino acid sensitive reagents for the detection of latent fingermarks is a valid technique in forensic chemistry. Fingerprints Fingerprints are unique to each individual, and have been used as identification tools in law enforcement since 1892. “Every contact leaves a trace.” Two types • visible: visible with the naked eye • latent: hidden residue left on surface, require chemical treatment or powders to allow visualization Visualization of Latent Fingermarks • Development produces visible colour • Photoluminescence – the process by which a substance absorbs a photon and re-emits photons, producing colour – Observed by illuminating developed fingermark with a filtered light source, viewing through appropriate filters • Developed fingermark photographed Friction Ridge Patterns • Development of latent prints depends on composition of the print • Eccrine and sebaceous glands • Amino acids are found in eccrine secretions • Tight binding leads to long lifetime • Non-specific reagents optimal Keys to a Good Reagent 1. An appropriate medium for the reagent 2. A method of bringing the reagent and the item of interest into contact 3. Providing appropriate reaction conditions Ninhydrin • Predominant reagent used for visualization • Reacts with amino acids to produce Ruhemann’s Purple • Strong absorption band • Viewable with white light • Addition of metal salts causes colour change and fluorescence • Due to increased rigidity of pi system • Cooling with liquid nitrogen increases luminescence • Heating increases reaction rate, decreases contrast Ninhydrin Analogues • Search for better visible contrast and luminescence • Electron donating and accepting groups create variation in colour and luminescence • Compounds with similar structure investigated for potential as fingermark reagents DFO (1,8-diasafluoren-9-one) • Forms red product which luminesces under laser or alternate light source • Similar mechanism to ninhydrin • Heat required for development of print • Excess heat and humidity decrease luminescence • “DFO-dry” • No secondary treatment required • Simple work-up technique 1,2-indanedione • Forms pale pink colour • Intense room-temperature luminescence • Metal salt addition increases luminescence intensity • Heating not necessary, can be used to accelerate development Alternative • Fluoroscamine, o-phthalaldehyde and NBDchloride researched as prospects • UV-light interference • Background interference Natural Products • React with amino acids, need no further treatment • Improved signal to noise ratio due to luminescence at longer wavelengths • Additional research required • Genepin • Lawsone • Naphthaquinones Comparison • Conditions of development have a large impact on contrast and luminescence of fingermark produced • Ninhydrin better than both DFO and 1,2indanedione for colour contrast • DFO and 1,2-indanedione create more sensitive luminescence than ninhydrin Conclusion • There are no optimal condition, therefore there can be no globally accepted reagent • Ninhydrin and its analogues have been shown to be sufficiently useful in developing latent fingermarks by reacting with amino acids. • Can be used alone or in succession depending on conditions References • Jelly, R., Lennard, C., Lewis, S. W., Lim, K.F., Patton, E.L.T., The Detection of Latent Fingermarks on Porous Surfaces Using Amino Acid Sensitive Reagents: A Review Analytica Chimica Acta. 2009 vol 652, pp. 128 – 142