Coating Approach Clears Up Fingerprints

CSI notwithstanding, forensics experts cannot always retrieve fingerprints from objects, but a conformal coating process developed by Penn State professors can reveal hard-todevelop fingerprints on nonporous surfaces without altering the chemistry of the print.

As prints dry or age, the common techniques used to develop latent fingerprints, such as dusting or cyanoacrylate – SuperGlue – fuming often fail,” said Robert Shaler, professor of biochemistry and molecular biology and director of Penn State’s forensic sciences program.

Three sebaceous fingermarks were deposited on a glass slide. The slide was then coated with a columnar thin film of magnesium fluoride.
Three sebaceous fingermarks were deposited on a glass slide. The slide was then coated with a columnar thin film of magnesium fluoride. The film thickness was about 125 nm. The fingermarks are clearly developed by this process.

The conformal coating applications suggested by Shaler and Akhlesh Lakhtakia, Charles Godfrey Binder Professor of Engineering Science and Mechanics, use the physical properties of the fingerprint, not the chemistry of the substances left behind. In fact, the researchers believe that even after the fingerprints are developed using the coating, forensics experts could sample the fingerprint material to determine specifics about the person who left the prints.

The researchers used a form of physical vapor deposition – a method that uses a vacuum and allows vaporized materials to condense on a surface creating a thin film.

Normally, the deposition process requires exceptionally clean surfaces because any speck of dust or grease on the coated surface shows up as a deformity. However, with fingerprints, the point is to have the surface material’s ridges and valleys – topography – show up on the new surface so analysts can read them using an optical device without the necessity of chemical development or microscopy.

One benefit of this approach would be the ability to retrieve fingerprints off fragments from incendiary or explosive devices and still be able to analyze the chemicals used in the device.

The researchers tested two materials for coating, magnesium flouride and chalcogenide glass – a combination of germanium, antimony and selenium. The coating material is heated in a vacuum, while the artifact to be coated is rotated fairly quickly to allow deposition over the entire surface.

The researchers tried coating a variety of fingerprints on glass and even on tape. They coated pristine fingerprints and those that had been fumed with SuperGlue. In all cases, the coated fingerprints were usable. The equipment used to deposit the coating is a laboratory device, but it can produce the coating in about 15 minutes. The researchers would like to design a portable device that could be brought to a crime scene and produce readable fingerprints on site.

Shaler and Lakhtakia have filed a provisional patent application on this application.

Robert Shaler is a professor of biochemistry and molecular biology and director of Penn State's forensic sciences program. Dr. Akhlesh Lakhtakia is a Charles Godfrey Binder professor of engineering science and mechanics.

This Research Snapshot is condensed from a news release on Penn State Live by A’ndrea Elyse Messer, Ph.D.

This article was featured in Focus on Materials - Fall 2010.