Latent fingermark detection using amino acid sensitive reagents

1. Latent fingermark detection using amino acid sensitive reagents

2. Introduction The use of amino acid sensitive reagents for the detection of latent fingermarks is a valid technique in forensic chemistry.

3. 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

4. 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

5. 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

6. Keys to a Good Reagent • An appropriate medium for the reagent • A method of bringing the reagent and the item of interest into contact • Providing appropriate reaction conditions

7. Ninhydrin • Predominant reagent used for visualization • Reacts with amino acids to produce Ruhemann’s Purple • Strong absorption band • Viewable with white light

8. 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

10. 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

12. 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

13. 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

14. Alternative • Fluoroscamine, o-phthalaldehyde and NBD-chloride researched as prospects • UV-light interference • Background interference

15. 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

16. 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

17. 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

18. 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