In forensic DNA analysis, evidence sampling stands as a pivotal step setting the ground for the quality of the forensic profiling. The collection of touch DNA from objects, when guidelines are scarce or absent, is usually governed by ad hoc decisions based on the available case circumstances. In our laboratory, in the context of illicit drug-related crimes, similar objects are frequently encountered, offering an opportunity for the standardization of evidence treatment. This study aims to develop an effective method for sampling touch DNA from knots on plastic bags. We examine both the exposed and hidden areas of knots, considering the latter as "protected" zones less likely to accumulate biological material during subsequent handling. The study contrasts a single sample method (whole knot surface sampling, Method 1) with dual-sample methods that separate exterior (exposed) and interior (hidden) surfaces of the knot. Notably, our study consistently reveals higher DNA yields from exterior surfaces of the knots as opposed to interior samples. Importantly, our findings demonstrate that utilizing a single sample may produce DNA profiles that are not interpretable, while employing a dual-sample approach may allow for the differentiation between the genetic contributions of the person who tied the knot, the packer, from the person who held the package, the holder. We have refined the dual-sample method to reduce holder DNA in the interior sample while maintaining it on the exterior, also allowing the packer's DNA to be detected on both surfaces. We explore four dual-sample collection methods. Method 2 involves taking the first sample from the exterior and the second from the interior of an untied knot. Method 3 visually differentiates between the original exposed and hidden surfaces for precise sampling. Method 4 employs tools to open the knot for interior sampling. Method 5 uses Diamond dye to highlight cell-free DNA on both surfaces before sampling. In conclusion, this study not only clarifies the complex dynamics of touch DNA transfer and collection on plastic bag knots, but also offers insights into standardizing evidence collection in similar cases.

中文翻译：

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对塑料袋结进行精确接触 DNA 采样，以改进包装者和持有人贡献的分析


在法医 DNA 分析中，证据采样是为法医分析质量奠定基础的关键步骤。当指导方针稀缺或缺乏时，从物体中收集接触DNA通常是根据现有的案例情况做出临时决定。我们实验室在毒品犯罪的背景下，经常会遇到类似的物品，这为证据处理的标准化提供了机会。本研究旨在开发一种从塑料袋结上采样接触 DNA 的有效方法。我们检查了结的暴露区域和隐藏区域，将后者视为“保护区”，在后续处理过程中不太可能积累生物材料。该研究将单样本方法（整个结表面采样，方法 1）与将结的外（暴露）表面和内（隐藏）表面分开的双样本方法进行了对比。值得注意的是，我们的研究一致表明，与内部样本相比，结外表面的 DNA 产量更高。重要的是，我们的研究结果表明，使用单个样本可能会产生不可解释的 DNA 图谱，而采用双样本方法可能会区分打结者（打包者）和打包者的遗传贡献。持有包裹，持有人。我们改进了双样本方法，以减少内部样本中的持有者 DNA，同时将其保留在外部，还允许在两个表面上检测加壳者的 DNA。我们探索了四种双样本收集方法。方法 2 涉及从解开的结的外部获取第一个样本，从内部获取第二个样本。 方法 3 在视觉上区分原始暴露表面和隐藏表面，以实现精确采样。方法4 使用工具打开结进行内部采样。方法 5 在采样前使用钻石染料突出显示两个表面上的游离 DNA。总之，这项研究不仅阐明了塑料袋结上接触 DNA 转移和收集的复杂动态，而且还为类似案件中标准化证据收集提供了见解。