ABSTRACT
Due to recent improvements in forensic DNA testing kit sensitivity, there has been an increased demand in the criminal justice community to revisit past convictions or cold cases. Some of these cases have little biological evidence other than touch DNA in the form of archived latent fingerprint lift cards. In this study, a previously developed optimised workflow for this sample type was tested on aged fingerprints to determine if improved short tandem repeat (STR) profiles could be obtained. Two-year-old samples processed with the optimised workflow produced an average of approximately five more STR alleles per profile over the traditional method. The optimised workflow also produced detectable alleles in samples aged out to 28 years. Of the methods tested, the optimised workflow resulted in the most informative profiles from evidence samples more representative of the forensic need. This workflow is recommended for use with archived latent fingerprint samples, regardless of the archival time.Key pointsThe use of the optimised workflow on aged archived latent fingerprint (ALFP) lift card samples (aged 2-28 years) improves the number of STR alleles recovered, providing more discriminatory STR profiles than those processed using the traditional workflow.Interpretable STR alleles can be detected from ALFP lift card samples stored as long as 28 years when the optimised procedures are followed.The use of individual laboratory-sterilised tools for sample preparation and the addition of a re-purification step with Centri-Sep columns in the recommended optimised workflow seem to limit the ability to detect low-level secondary DNA sources.
ABSTRACT
As DNA technology becomes increasingly sensitive, forensic laboratories are receiving more low-template DNA samples. These samples, already low in DNA content, become even more challenging to process as the available DNA becomes further reduced during the extraction step. In this study, two extraction modifications were tested to determine if the cause of DNA loss could be identified and mitigated. A double lysis technique was used to test for DNA loss in the sample collection substrate, and lysate eluates were re-extracted to determine DNA loss from inefficient binding to the silica column. Both modifications showed DNA was lost at these steps. However, resulting STR profiles from these samples had fewer peaks and lower peak heights when compared to samples processed with no extraction modifications. Overall, the potential benefits of adding these extraction modifications for low-template DNA sample processing are not enough to justify the risk associated with additional manipulation.
Subject(s)
DNA Fingerprinting , DNA/isolation & purification , Forensic Genetics/methods , Cell Membrane , Humans , Microsatellite Repeats , Polymerase Chain ReactionABSTRACT
DNA profiles have been obtained from fingerprints, but there is limited knowledge regarding DNA analysis from archived latent fingerprints-touch DNA "sandwiched" between adhesive and paper. Thus, this study sought to comparatively analyze a variety of collection and analytical methods in an effort to seek an optimized workflow for this specific sample type. Untreated and treated archived latent fingerprints were utilized to compare different biological sampling techniques, swab diluents, DNA extraction systems, DNA concentration practices, and post-amplification purification methods. Archived latent fingerprints disassembled and sampled via direct cutting, followed by DNA extracted using the QIAamp® DNA Investigator Kit, and concentration with Centri-Sep™ columns increased the odds of obtaining an STR profile. Using the recommended DNA workflow, 9 of the 10 samples provided STR profiles, which included 7-100% of the expected STR alleles and two full profiles. Thus, with carefully selected procedures, archived latent fingerprints can be a viable DNA source for criminal investigations including cold/postconviction cases.
