Visualizing Shed Skin Cells in Fingerprint Residue using Dark Field Microscopy
Shinichiro N. Muramoto, William Alexander Osborn, J Greg Gillen
The proof of concept study was able to show that dark field microscopy could be used to provide sufficient contrast for cell visualization in fingerprints with high sebum content. Although the application is limited to smooth surfaces that do not scatter light, such as polyethylene terephthalate (PET), it was able to measure the number of cells and how they changed in sequentially deposited fingerprints. On a PET surface, at roughly 5 N of contact force, a typical finger initially transferred a few hundred cells onto the surface, and when deposited in sequence this number decreased exponentially until a steady state was reached. The steady state was characterized by a transfer of (78 ± 36) cells, or (0.46 ± 0.21) cells/mm2 when normalized for fingerprint area. The high uncertainty was due in part to the highly variable nature of a human finger where the number of loose cells vary from person to person and from day to day depending on what they touch. The other part was due to difficulties in controlling the contact force and finger movement such as twisting during deposition. It was shown that slight twisting of the finger can expose a new patch of skin to the substrate, increasing the number of cell transfer.
Journal of Forensic Sciences
fingerprint, shed skin cells, dark field, optical microscopy