Collecting touch DNA from glass surfaces using different sampling solutions and volumes: Immediate and storage effects on genetic STR analysis

Abstract

Touch DNA has become increasingly important evidence in todays' forensic casework. However, due to its invisible nature and typically minute amounts of DNA, the collection of biological material from touched objects remains a particular challenge that underscores the importance of the best collection methods for maximum recovery efficiency. So far, swabs moistened with water are often utilized in forensic crime scene investigations for touch DNA sampling, even though an aqueous solution provokes osmosis, endangering the cell's integrity. The aim of the research presented here was to systematically determine whether DNA recovery from touched glass items can be significantly increased by varying swabbing solutions and volumes compared with water‐moistened swabs and dry swabbing. A second objective was to investigate the possible effects of storage of swab solutions prior to genetic analysis on DNA yield and profile quality when stored for 3 and 12 months, as is often the case with crime scene samples. Overall, the results indicate that adapting volumes of the sampling solutions had no significant effect on DNA yield, while the detergent‐based solutions performed better than water and dry removal, with the SDS reagent yielding statistically significant results. Further, stored samples showed an increase in degradation indices for all solutions tested, but no deterioration in DNA content and profile quality, allowing for unrestricted processing of touch DNA samples stored for at least 12 months. One further finding was a strong intraindividual change in DNA amounts observed over the 23 deposition days which may be related to the donor's menstrual cycle.

Exploring the potential of genetic analysis in historical blood spots for patients with iodine-deficient goiter and thyroid carcinomas in Switzerland and Germany (1929–1989)

“…With respect to subsequent downstream analysis, it is essential to note that a low quantification result does not necessarily result in a profiling failure using standard forensic amplification kits, which, however, remains to be investigated for further in-depth downstream genetic analyses. For example, research demonstrated that DNA profiles could be generated from samples with literally no DNA quantities [ 39 , 50 ]. Moreover, the alleged imprints of the medical records before 1940 posed a challenge in differentiation from the paper discoloration that occurs with the age of the patient’s files and/or medical illustrations that inherently lack DNA content.…”

“…From a forensic standpoint, it remains controversial whether the majority of the detected DNA quantities are appropriate for additional analyses, including classical short tandem repeat (STR) analysis utilizing multiplex polymerase chain reaction (PCR) or using single nucleotide polymorphisms (SNPs) and next-generation sequencing (NGS) [ 70 – 72 ]. Recent advances in the sensitivity of techniques and reagents have enabled DNA profiling from quantities as low as contact traces [ 50 , 73 ] or even individual cells [ 74 ]. Further, NGS has successfully analyzed degraded samples from human remains and artificially degraded DNA through UV treatment [ 75 ].…”

What Are the Limitations and Challenges of Swab-Based DNA Sampling?

“…Schulte et al concluded that the prewetting volume has no significant effect on DNA yield and that 70% ethanol and 0.10% v/v Triton X-100 are both suitable as moistening solutions for the collection of touch DNA. Also, SDS can be used but tends to foam when higher concentrations are used, and Triton X-100 is extremely viscous, which makes its handling more difficult [27]. Canfield et al recommend the use of AutoMACS running buffer (containing BSA, EDTA, and azide) for the recovery of intact leukocytes over PBS or water in combination with nylon-flocked swabs (instead of cotton or dissolvable swabs) [28].…”