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Latent fingermark detection using amino acid sensitive reagents
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Introduction
The use of amino acid sensitive reagents for the detection of latent fingermarks is a valid
technique in forensic chemistry.
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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
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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
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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
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Keys to a Good Reagent
1. An appropriate medium for the reagent2. A method of bringing the reagent and the
item of interest into contact3. Providing appropriate reaction conditions
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Ninhydrin
• Predominant reagent used for visualization• Reacts with amino acids to produce
Ruhemann’s Purple • Strong absorption band
• Viewable with white light
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• 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
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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
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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
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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
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Alternative
• Fluoroscamine, o-phthalaldehyde and NBD-chloride researched as prospects
• UV-light interference• Background interference
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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
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Comparison
• Conditions of development have a large impact on contrast and luminescence of fingermark produced
• Ninhydrin better than both DFO and 1,2-indanedione for colour contrast
• DFO and 1,2-indanedione create more sensitive luminescence than ninhydrin
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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
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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