Improving fingerprint identification
A new approach for making finger prints on paper more visible has been developed by scientists at the Hebrew University of Jerusalem.
The method uses an innovative chemical process which produces a negative of the fingerprint image. Unlike current methods, which use the positive image, the new process leaves almost no sweat residue behind on the paper.
“Since our method relies only on the fatty components in the fingerprints, the sweaty aspects play no role in the imaging process,” said Professor Yossi Almog, who led the research.
Studies have shown that using the conventional fingerprinting method, less than half of the fingerprints on paper items can be made sufficiently visible to enable their identification. Variable sweat residue seems to be predominantly responsible for this.
The new procedure avoids this problem via inversion of an established method in which gold nanoparticles are first deposited onto the invisible fingerprints, followed by elemental silver. The technique is thus similar to the development of a black and white photograph.
Conventional fingerprinting allows gold particles to stick to the amino acid components of the sweat in the fingerprints, and then silver is deposited onto the gold. This technique often results in a relatively low-contrast image which is difficult to see clearly.
In the new technique, the gold nanoparticles stick directly to the paper surface, not to the sweat. This method uses the sebum from the fingerprints as a medium to avoid this interference. The paper is then treated with a developer containing silver which turns the areas with gold on them black, resulting in a clear, negative image of the fingerprint.
Almog also pointed out that the new technique promises to alleviate another common problem with conventional forensics: “If paper becomes 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,” he said.
The method is described in Angewandte Chemie.