What Are the Limitations and Challenges of Swab-Based DNA Sampling?
Brigitte Bruijns
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Abstract:
Selecting the optimal sampling method is an essential component of the DNA analysis process. Errors or omissions in targeting and gathering relevant samples can significantly reduce the likelihood of obtaining a valuable DNA profile, affecting the profile's quality and evidential value and ultimately hindering its ability to support the justice system. While DNA typing techniques have become significantly more sensitive in recent years, there is an ongoing need for further advancements in the recovery of DNA from crime scenes. It is essential to improve the accuracy and reliability of forensic investigations, particularly in cases where only tiny amounts of DNA are present, such as touch DNA samples or degraded forensic evidence. Parameters, including swab material, type of substrate, and swabbing protocol, that influence the efficiency of a swab are discussed in this review. This is followed by a literature review of studies that have compared swab types and/or other sampling conditions. While swabs are the most-used collection tools at a crime scene, alternatives are available. These alternatives are reviewed, including their advantages and disadvantages. A critical discussion and conclusions make clear that, unfortunately, neither swabs nor their alternatives are highly effective in recovering DNA from a substrate.
Introduction
Using a swab to collect forensically relevant samples, including buccal swabs for reference, is a common method for recovering biological material from a crime scene. A swab can be defined as an absorbent pad with a shaft. Originally designed as ‘ear pickers’, swabs are now used for various purposes, including sample collection (e.g., microorganisms, DNA/RNA, and forensic traces) [1–3].
The use and selection of the most appropriate swab type received much attention during the COVID-19 pandemic, since swabs are a fundamental tool in collecting samples from individuals to diagnose the presence of the SARS-CoV-2 virus [4].
In this review, the performance of swabs is examined closely. The overall performance or efficiency is composed of the extraction efficiency and the recovery efficiency, and the absorption capacity plays a role. These terms are explained in the next section, along with the various factors influencing these efficiencies, such as the swab material and the type of substrate. Subsequently, a critical reflection of swab performance as reported in the literature is provided. Since swabs generally exhibit low overall efficiency, various available alternatives are discussed. In the Discussion, the performance of swabs and their alternatives is analyzed in light of the various factors that influence efficiency. Moreover, a critical reflection is given on the other criteria that determine the selection of a swab, such as the usability of a swab or alternatives.
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Copyright: © 2024 by the author. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License which permits unrestricted noncommercial use, distribution, and reproduction, provided the original work is properly cited and not changed in any way.