New Technique Makes It Possible To Decipher Fingerprints Left On Paper
Television series like CSI and Criminal Minds would have us believe that nothing is easier than gathering fingerprints at crime scenes. In reality, finding prints on many surfaces, such as paper, is a near impossible task.
Being able to read prints left on checks, bank notes etc. is crucial to investigations, yet studies have shown that less than half of fingerprints on paper can be made sufficiently visible to enable their identification. The main reason for this seems to be the highly variable composition of the sweat left behind on the paper.
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The golden solution
The technique involves an inversion of an established method in which gold nanoparticles are first deposited onto the invisible fingerprints, followed by elemental silver, similar to the development of a black and white photograph.
In the conventional technique, the gold particles get stuck to the amino acid components of the sweat in the fingerprints, and then silver is deposited onto the gold. The result is quite often low-contrast impressions of the fingerprints. With the new method developed at the Hebrew University, the gold nanoparticles stick directly to the paper surface, but not the sweat. This technique utilizes the sebum (an oily substance secreted by the sebaceous glands that helps prevent hair and skin from drying out) from the fingerprints as a medium to avoid this interference. Treatment with a developer containing silver then turns the areas with gold on them black, resulting in a clear, negative image of the fingerprint.
“Since our method relies only on the fatty components in the fingerprints, the sweaty aspects play no role in the imaging process,” said Prof. Almog. This technique also promises to alleviate another problem, he said. “If paper has become wet, it has previously been difficult to detect fingerprints because the amino acids in the sweat, which are the primary substrate for current chemical enhancement reactions, are dissolved and washed away by water, whereas the fatty components are barely affected.”
Photo by Heberw University