Nanoparticle attraction key to forensics

A team of researchers from the University of Lausanne, Switzerland has shed new light on the mechanisms responsible for a nanoparticles’ ability to detect finger-marks left at crime scenes.

Until now, researchers wrongly theorised as to why nanoparticles were attracted to fingerprints.

“There are number of different techniques used to visualise finger-marks when they are brought into the lab; however, they all lack sensitivity

Lead author Sebastien Moret

However, in results published today in the journal Nanotechnology, the Swiss-based research team claims a nanoparticles’ attraction is actually chemical, rather than electrostatic, and is caused by compounds on the surface of nanoparticles bonding with a ’complex cocktail’ of compounds present in finger-mark residue.

According to research, nearly 50% of marks left on paper, for example, remain undetected.

Lead author Sebastien Moret said: “There are number of different techniques used to visualise finger-marks when they are brought into the lab; however, they all lack sensitivity.

“Some of these techniques show an affinity not only for finger-marks, but also for the substrate or surface that the mark was left on, leading to background staining that conceals the finger-mark.”

Moret said that the majority of these techniques were developed through a “trial and error” approach, suggesting it is imperative that researchers gain a deeper understanding of the fundamental mechanisms that are involved.

To conduct the study, researchers deposited finger-marks onto aluminium foil and then submerged them in an aqueous solution containing silicon dioxide (SiO2) nanoparticles which had been coated with a chemical group, known as carboxyl, which is made up of carbon, hydrogen and oxygen atoms.

According to the researchers, a number of tests indicated that the attraction between the nanoparticles and the finger-marks was occurring because of a chemical bond between the carboxyl group and a specific chemical group, called an amine group, which was present in the amino acids and proteins in the finger-mark residue.

“Now that it has been established that a chemical interaction can be promoted between nanoparticles and a specific chemical group within the finger-mark residue, this interaction can be further promoted, leading to more precise targeting, increased selectivity and the reduction of background noise,” Moret said.

“Since one chemical group from the finger-mark residue has been targeted, others can be targeted as well, thus multiplying the chances of detecting previously undetectable finger-marks.”