Forensic Spectroscopic Chemical Fingerprinting of Fingerprints
THE MICROSCOPE
2014, Volume 62:4, pp. 147–154
DOI
https://doi.org/10.59082/MROB7268
AUTHORS
David L. Wetzel, Mark D. Boatwright and Jarrod B. Bechard
ABSTRACT
The art of lifting human fingerprints and their utility in forensic science is well established. The potential of linking the chemical deposition of the fingerprint with prior topical environmental contact has not yet been fully realized. Infrared microspectroscopy (IR) with a 10 x 10 μm aperture enables obtaining chemical data from a single fingerprint ridge. The prevalent use of skin treatment via health and beauty products, if detected, may reveal the nature of the unintended deposition. We chose skin treatment contact to illustrate this feature because each particular pharmaceutical company has its own formulation that may leave a distinctive infrared chemical fingerprint. An infrared spectral library of more than 50 different commercial products was established using transmission reflection from a polished stainless plate or an infrared-reflecting glass microscope slide. Transfer of the product to the finger was completed from a thincoated surface. The fingerprint ridge deposited on a clean, hard surface was subjected to IR to obtain the spectrum to reveal the chemical identity of the residue transferred from the finger. Initial classification of the library spectra was by the prevalence of the carrier solvent type from prominent stretching vibrations, and their individuality was recognized by the pattern of the infrared fingerprint region. Discriminant analysis algorithms were employed to enable objective matching of the spectrum obtained from the actual fingerprint with a particular cosmetic or healthcare product. This modest effort is intended to demonstrate the potential of the infrared microspectroscopic forensic approach. Spectra are presented to illustrate the utility of infrared microspectroscopic fingerprinting of fingerprints.