Visualizing shed skin cells in fingerprint residue using dark‐field microscopy

This proof‐of‐concept study shows that dark‐field microscopy provides 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...

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Bibliographic Details
Published inJournal of forensic sciences Vol. 66; no. 4; pp. 1257 - 1266
Main Authors Muramoto, Shin, Osborn, William, Gillen, Greg
Format Journal Article
LanguageEnglish
Published United States Wiley Subscription Services, Inc 01.07.2021
Subjects
cell count
Contact force
dark field
fingermark
fingerprint
Fingerprints
Microscopy
Optical microscopy
Plasma etching
Polyethylene terephthalate
Residues
skin cells
Substrates
Twisting
Twisting movement
skin cells
dark field
fingerprint
cell count
fingermark
optical microscopy
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Summary:This proof‐of‐concept study shows that dark‐field microscopy provides 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 deposited within a fingerprint residue and the reduction in cell transfer with repeated skin contact. On a PET surface, at roughly 5 N of contact force, a typical finger transfers several hundred cells onto the surface. Over subsequent finger contacts onto a clean PET surface, this number decreased exponentially until a steady state was reached, which is characterized by the transfer of (78 ± 36) cells or (0.46 ± 0.21) cells/mm2 when normalized for fingerprint area. High uncertainty in cell transfer was due to: the highly variable nature of a human finger (where the number of loose cells varies from person to person and from day to day depending on what they touch) and difficulties in controlling the contact force and finger movement such as twisting during deposition (where twisting of the finger can expose a new patch of skin to the substrate, increasing the number of cell transfer). Plasma etching was also explored as an effective way to validate dark‐field microscopy for cell counting. Although limited to inorganic substrates due to etching effects, exposing the fingerprint for less than 10 min can remove a majority of the sebum while keeping the cells intact for a before‐and‐after comparison using light microscopy.
Bibliography:Funding information
Certain commercial equipment, instruments, or materials are identified in this paper to adequately specify the experimental procedure. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.
Funding was provided by the Intelligence Advanced Research Projects Activity (IARPA) under Contract # IARPA‐16002‐D2019‐1908050003.
The opinions, findings, and conclusions expressed here are those of the author and do not necessarily reflect those of the funding organizations.
Collection and handling of samples involving human subjects were approved and conducted in accordance to guidelines set forth by the NIST Institutional Review Board, case # MML‐2018‐0074. Volunteers who participated in this study read the information sheet before donating fingerprints. Each volunteer was assigned with a code to anonymize the sample. Five volunteers contributed to this study.
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ISSN:0022-1198
1556-4029
DOI:10.1111/1556-4029.14707