Transcript Latent fingermark detection using amino acid sensitive reagents

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