Abstract：
According to the principle of Locard \"Every contact leaves a trace\", when touching a surface, a bi-directional transfer of self and non-self-DNA residing on the hands and touched objects can occur. Metals are commonly encountered in forensic evidence and, during hand contact with these surfaces, a transfer of metal particles could occur together with the transfer of human DNA. This study proposes a proof-concept approach for the original detection of metal particles and touch DNA to track the activity performed by a donor and particularly to assess the metallic substrate touched before the contact with a subsequent surface. To this scope, a scenario of contact events was simulated by three volunteers, who participated in fingerprint deposition firstly on copper and then on plastic and glass surfaces. Twenty-four stubs were collected on the hands of volunteers and the secondary surfaces and then analyzed by environmental scanning electron microscopy (ESEM). DNA was quantified only from copper and plastic surfaces. Ten additional volunteers followed the same protocol of deposition on copper and then on plastic surfaces to evaluate DNA transfer only. On 20 touch DNA samples, the copper surface yielded significantly lower DNA amounts, ranging from 0.001 to 0.129 ng/μl, compared to the secondary touched plastic surface, ranging from 0.007 to 0.362 ng/μl. ESEM-EDS analysis showed that copper particles could be abundantly detected on the hands of the volunteers after contact with the copper surface. Particles containing silicates with copper were shown on plastic, while they were only found in 1/3 of samples on glass. Our proof-of-concept study has shown that ESEM-EDS analysis has the potential to detect copper particles transferred to the hands of volunteers during contact with a copper metallic surface and deposited on secondarily touched items. The results suggest that this original ESEM-DNA parallel approach could potentially allow the tracking of DNA transfer and metal particles at a crime scene, although this represents only a first step and further research on a wider casuistry could help to address the interpretation of results given activity level propositions.
摘要：
根据洛卡尔的原则，“每个接触都会留下痕迹”，当接触表面时，可以发生驻留在手和触摸物体上的自我和非自我DNA的双向转移。金属通常在法医证据中遇到，用手接触这些表面时，金属颗粒的转移可能与人类DNA的转移一起发生。这项研究提出了一种验证概念方法，用于对金属粒子和触摸DNA进行原始检测，以跟踪供体进行的活动，特别是在与后续表面接触之前评估接触的金属基材。在这个范围内，三名志愿者模拟了接触事件的情景，他首先在铜上，然后在塑料和玻璃表面上参与指纹沉积。在志愿者的手上和次要表面上收集了二十四个短柱，然后通过环境扫描电子显微镜（ESEM）进行分析。仅从铜和塑料表面定量DNA。另外10名志愿者遵循相同的方案，即在铜上沉积，然后在塑料表面上沉积，以仅评估DNA转移。在20个触摸DNA样本上，铜表面产生的DNA量明显较低，范围从0.001到0.129ng/μl，与二次接触的塑料表面相比，范围从0.007到0.362ng/μl。ESEM-EDS分析表明，与铜表面接触后，在志愿者的手上可以大量检测到铜颗粒。含有硅酸盐和铜的颗粒显示在塑料上，而它们只在1/3的玻璃样品中发现。我们的概念验证研究表明，ESEM-EDS分析有可能检测在与铜金属表面接触并沉积在二次接触物品上的过程中转移到志愿者手中的铜颗粒。结果表明，这种原始的ESEM-DNA平行方法可能允许在犯罪现场跟踪DNA转移和金属颗粒，虽然这只是第一步，对更广泛的证据的进一步研究可能有助于解决给定活动水平命题的结果解释。
