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 reagent2. A method of bringing the reagent and the

item of interest into contact3. 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 NBD-chloride 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 1,2-indanedione 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