Assessment and prevention of forensic DNA contamination in DNA profiling from latent fingerprint

In this study, fingerprint brush contamination and a simple brush cleaning procedure was assessed. A total of 10 new camel-hair fingerprint brushes were used for dusting either fresh saliva or saliva stain prior to dusting 4 latent fingerprints deposited on the glass surface. Ten hairs were cut from each fingerprint brush and 4 latent fingerprints were collected by double swab technique for DNA analysis. Consensus DNA profiles were generated from 3 replications of the samples. Result showed that mixed DNA profiles were obtained from the latent fingerprint swabs. More than 2 alleles were observed, and matched alleles from the saliva and fingerprint donors. DNA profiles generated from the brush hairs had no complete loci. The called alleles matched the saliva donor and some were shared alleles of the 2 contributors. Amount of DNA deposited on fresh-saliva contaminated brushes were higher than that those contaminated with saliva stain. Next, fingerprint brushes were cleaned with dish-washing liquid and rinsed with sterile-water. DNA profiling of 5 cleaned-brushes showed that no consensus DNA profile was obtained. Although few alleles were called in each replication of the DNA profile, they were not reproducible. The persistence of biological material on fingerprint brush hairs was demonstrated, thus being a potential source of contamination by indirect material transfer. Cleaning fingerprint brush after direct exposure to biological fluid and stains could help to prevent evidence cross-contamination.