Assessment and mitigation of DNA loss utilizing centrifugal filtration devices.

Maximizing DNA recovery during its isolation can be vital in forensic casework, particularly when DNA yields are expected to be low, such as from touch samples. Many forensic laboratories utilize centrifugal filtration devices to purify and concentrate the DNA; however, DNA loss has been reported when using them. In this study, all centrifugal filtration devices tested caused substantial DNA loss, affecting low molecular weight DNA (PCR product) somewhat more than high molecular weight DNA. Strategies for mitigating DNA loss were then examined, including pre-treatment with glucose, glycogen, silicone (RainX(®)), bovine serum albumin, yeast RNA, or high molecular weight DNA. The length of pre-treatment and UV irradiation of pre-treatment reagents were also investigated. Pre-treatments with glucose and glycogen resulted in little or no improvement in DNA recovery, and most or all DNA was lost after silicone pre-treatment. Devices pre-treated with BSA produced irregular and uninterpretable quantitative PCR amplification curves for the DNA and internal PCR control. On the other hand, nucleic acid pre-treatments greatly improved recovery of all DNAs. Pre-treatment time and its UV irradiation did not influence DNA recovery. Overall, the results show that centrifugal filtration devices trap DNA, yet their proper pre-treatment can circumvent that loss, which is critical in the case of low copy forensic DNA samples.

Collecting and analyzing DNA evidence from fingernails: a comparative study.

Forensic practitioners and crime laboratories regularly collect and analyze fingernail evidence; however, the best techniques for processing such evidence have not been established. In this study, numerous aspects of fingernail evidence processing-collection of exogenous cells, transportation, purification of DNA, and STR analysis-were analyzed using fingernails harboring applied blood or epithelial cells from scratchings. Autosomal STR mixtures resulted when fingernails were soaked or swabbed, while scrapings rarely generated mixtures but exhibited allelic dropout. Y-STRs yielded single source profiles, with scrapings again showing dropout. A silica-based kit extraction recovered significantly more exogenous DNA than did organic extraction, neither of which was affected by nail polish. Swabbing nails in succession resulted in some cross-contamination from exogenous material, while transporting nails together did not, although there was loss of exogenous cells. Optimized nail processing produced complete Y-STR profiles of male volunteers from female fingernails following scratchings.