Artificial fingerprints for cross-comparison of forensic DNA and protein recovery methods

Abstract

Quantitative genomic and proteomic evaluation of human latent fingerprint depositions represents a challenge within the forensic field, due to the high variability in the amount of DNA and protein initially deposited. To better assess recovery techniques for touch depositions, we present a method to produce simple and customizable artificial fingerprints. These artificial fingerprint samples include the primary components of a typical latent fingerprint, specifically sebaceous fluid, eccrine perspiration, extracellular DNA, and proteinaceous epidermal skin material (i.e., shed skin cells). A commercially available emulsion of sebaceous and eccrine perspiration material provides a chemically-relevant suspension solution for fingerprint deposition, simplifying artificial fingerprint production. Extracted human genomic DNA is added to accurately mimic the extracellular DNA content of a typical latent print and comparable DNA yields are recovered from the artificial prints relative to human prints across surface types. Capitalizing on recent advancements in the use of protein sequence identification for human forensic analysis, these samples also contain a representative quantity of protein, originating from epidermal skin cells collected from the fingers and palms of volunteers. Proteomic sequencing by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis indicates a high level of protein overlap between artificial and latent prints. Data are available via ProteomeXchange with identifier PXD015445. By including known quantities of DNA and protein into each artificial print, this method enables total DNA and protein recovery to be quantitatively assessed across different sample collection and extraction methods to better evaluate extraction efficiency. Collectively, these artificial fingerprint samples are simple to make, highly versatile and customizable, and accurately represent the biochemical composition and biological signatures of human fingerprints.

Fig 1. Comparison of DNA yield and quality in latent and artificial fingerprints.

(A) Latent, loaded, and artificial fingerprints were deposited on two surfaces followed by DNA extraction to evaluate the total yield. (B) Comparison of DNA degradation index (DI) across fingerprint deposition on multiple surface types, where a DI ratio of greater than 1.0 indicates DNA degradation. AF (10), artificial fingerprints with 10 ng DNA; AF (5), artificial fingerprints with 5 ng DNA. Individual replicates are shown (circles) with the mean (bar) ± SD. For latent and loaded fingerprint samples, from both metal and glass, n = 6. For both types of artificial fingerprints, n = 3 for samples from glass and n = 5 for samples from metal.

Fig 2. Comparison of protein yield and quality between latent and artificial fingerprints.

(A) Comparison of ESM pre-homogenization (pre-homog., left) or following sieve-based homogenization (post-homog., right) shows reduction in the overall skin particle size. (B) Evaluation of ESM size in deposited latent (left), loaded (middle), or artificial (right) fingerprints on glass by light microscopy. (C) Representative SDS-PAGE results from an artificial fingerprint ESM range-finding experiment to determine the corresponding protein amount in typical latent fingerprints. Arrowheads indicate prominent bands found in both latent and artificial fingerprints. (D) Protein recovery measured by a Qubit fluorometric assay between latent and artificial fingerprint samples across two surface types. The amount of protein recovered was quantified and the relative amount normalized to the surface-specific latent print average. Individual replicates (n = 3) are shown (circles) with the mean (bar) ± SD.

Fig 3. Comparison of proteome composition between artificial and latent fingerprints.

(A) Protein sequence coverage (left) and number of peptides (right) detected for the fifty proteins with the highest mean sequence coverage detected in artificial or latent fingerprint samples. (B) Overlap of all proteins detected in artificial (AF) or latent (LF) fingerprint samples on metal (M) or glass (G) surfaces.

Fig 4. Development of simple and customizable artificial fingerprints.

Artificial fingerprints developed herein incorporate both protein and DNA, making these versatile surrogates for method development of human forensic technologies focused on DNA (STR or SNP analysis) or protein (GVP analysis) markers, with the ability to be customized based on the research needs.