Department of Forensic Science, Virginia Commonwealth University, Richmond, Virginia, United States of America.
Department of Physics, Virginia Commonwealth University, Richmond, Virginia, United States of America.
PLoS One. 2019 Feb 7;14(2):e0211810. doi: 10.1371/journal.pone.0211810. eCollection 2019.
A single focus optical tweezer is formed when a laser beam is launched through a high numerical aperture immersion objective. This objective focuses the beam down to a diffraction-limited spot, which creates an optical trap where cells suspended in aqueous solutions can be held fixed. Spermatozoa, an often probative cell type in forensic investigations, can be captured inside this optical trap and dragged one by one across millimeter-length distances in order to create a cluster of cells which can be subsequently drawn up into a capillary for collection. Sperm cells are then ejected onto a sterile cover slip, counted, and transferred to a tube for DNA analysis workflow. The objective of this research was to optimize sperm cell collection for maximum DNA yield, and to determine the number of trapped sperm cells necessary to produce a full STR profile. A varying number of sperm cells from both a single-source semen sample and a mock sexual assault sample were isolated utilizing optical tweezers and processed using conventional STR analysis methods. Results demonstrated that approximately 50 trapped spermatozoa were required to obtain a consistently full DNA profile. A complete, single-source DNA profile was also achieved by isolating sperm cells via optical trapping from a mixture of sperm and vaginal epithelial cells. Based on these results, optical tweezers are a viable option for forensic applications such as separation of mixed populations of cells in forensic evidence.
当激光束通过高数值孔径浸液物镜发射时，就会形成单焦点光镊。该物镜将光束聚焦到衍射极限光斑，从而创建一个光学陷阱，可将悬浮在水溶液中的细胞固定在其中。在法医调查中，精子通常是一种有证明力的细胞类型，可以被捕获在这个光学陷阱中，并逐个拖动毫米长度的距离，以创建一个细胞簇，随后可以将其吸入毛细管中进行收集。然后，将精子细胞喷射到无菌盖玻片上进行计数，并转移到管中进行 DNA 分析工作流程。本研究的目的是优化精子细胞的收集，以获得最大的 DNA 产量，并确定产生完整 STR 图谱所需的捕获精子细胞的数量。利用光镊从单个精液样本和模拟性侵犯样本中分离出不同数量的精子细胞，并采用常规 STR 分析方法进行处理。结果表明，大约需要 50 个捕获的精子才能获得一致的完整 DNA 图谱。通过从精子和阴道上皮细胞混合物中通过光学捕获分离精子细胞，还实现了完整的、单一来源的 DNA 图谱。基于这些结果，光镊是法医应用（例如分离法医证据中混合细胞群体）的一种可行选择。
