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