As we all know, fingerprint is called "human ID card", which is almost impossible to repeat, so it is often one of the most important evidences at the crime scene to help determine the identity of prisoners. But for some fingerprints with long time and small amount, it is difficult to show them by common techniques (such as powder method, reagent method, etc.). So people began to study the application of nanotechnology in fingerprint display, in which silica is regarded as the most promising nano material in this field.
Fingerprint display principle
If nanoparticles want to show fingerprint, they need to be coated with fluorescent material on their surface, and then through the adsorption of nanoparticle spheres and fingerprint residue, the corresponding color light will be emitted under the excitation of light wave in the wavelength of 425-450.
What is the specific "adsorption", which was widely accepted earlier is electrostatic adsorption theory, that is, through electrostatic energy, nanoparticles will be attracted to the fingerprint. But a recent paper in the journal nanotechnology refutes this theory, and the researchers believe that the reason why nanoparticles are attached to fingerprints is that there is a chemical bond between the nanoparticles and the compound that makes up the fingerprint residue.
In the experiment, the researchers printed the fingerprints on the surface of the aluminum foil, and then immersed them in the solution containing silica nanoparticles, which had been modified and wrapped by carboxyl groups containing carbon, hydrogen and oxygen atoms before. Next, the researchers added a specially designed dye to the nanoparticles, which can observe their attachment to fingerprints at a specific wavelength of light. The team repeated this process many times, proving that the reason why nanoparticles are attracted by fingerprint residues is that the carboxyl groups on the surface of silica and the amino acids on the fingerprint residues form chemical bonds.
Application status
Nano powder is not only used in the research of fingerprint. In 2010, a robbery happened in Putuo District of Shanghai. When the victim heard someone knock on the door, he opened the door. A man rushed into the room and tied Wang Jing with a sealed case belt to rob the property. Later, the police applied the nano particle display method, showing two fingerprints from the adhesive surface of the tape, which provided strong evidence for the detection of the case, enough to prove that the nano particle display method has been successfully applied to the actual case, and provided favorable technical support for the grass-roots front-line case.
Case diagram, not related to real case
However, in general, the current application of nano materials in fingerprint display is far from enough, the key is to find an efficient, non-toxic and cheap nano materials, silicon dioxide is undoubtedly a good choice. In addition, nano silica microspheres for fingerprint display need to meet the following requirements: functional groups with amino acid affinity on the surface, uniform particle size and good sphericity - functional groups can make nano silica particles selectively adsorb with potential fingerprints, and regular spheres can make silica produce directional regression hair under the irradiation of strong light source Shooting is good for observation and recognition.
The "omnipotence" of silica is always amazing. If it can be widely used, it will undoubtedly improve the success rate of fingerprint detection in crime scene. In the future, maybe we can see it and other new technologies in research appear in forensic investigation.
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