College of Science and Engineering, Flinders University, SA 5042, Adelaide, Australia.
College of Science and Engineering, Flinders University, SA 5042, Adelaide, Australia.
Forensic Sci Int. 2018 Oct;291:115-123. doi: 10.1016/j.forsciint.2018.08.016. Epub 2018 Aug 25.
Collection for touch DNA either at scenes or on items submitted to a forensic laboratory is based on assumptions as to where a person made direct contact. In many instances a swab may be applied to an area where no contact has been made. Many swabs may therefore be submitted for DNA profiling on which no DNA is present, resulting in the loss of both time and resources by analysing such swabs. This study has developed a simple, fast, DNA-staining and fluorescence microscopy-based screening method for swabs to indicate if there is any DNA from which to generate a profile. Ten different types of swabs were tested covering the major types used (foam, cotton and nylon). Each swab was treated by: no addition of dye or DNA, addition of dye only, addition of known DNA and addition of dye and DNA. The stain used was Diamond™ Nucleic Acid Dye (DD) and fluorescence microscopy was achieved with a digital microscope equipped with a blue LED light source (480nm) for excitation and an emission filter of 510nm. Two types of samples were tested, either buccal swabs or swabs collected from areas touched by volunteers and all analyses were performed in triplicate. The samples were collected and retained at room temperature with time intervals of 0 day, 7 days, 14 days, 21 days, and 28 days before detection using DD staining and fluorescence microscopy. Seven of the swab types used were found to be unsuitable due to the lack of any difference in the fluorescence detected when no DNA, or only the dye, or a combination of DNA and dye were added. Three swab types (black cotton swab, Ultrafine dental applicator, and Cylinder dental applicator) were found to be much more effective for collection of DNA. Further, stained cellular material retained its fluorescence for up to 4 weeks and swabs containing cellular material that had been stored for four weeks could be stained and visualised. Additionally, DD did not affect DNA profiling. This screening method has the potential to be a routine step in a forensic laboratory to save costs of processing samples where swabs are devoid of any DNA. This technique is rapid, easy, cheap, non-destructive and safe.
采集接触性 DNA 样本，无论是在现场还是提交给法医实验室的物品上，都是基于对人体直接接触部位的假设。在许多情况下，拭子可能会被应用于没有接触的区域。因此，许多拭子可能会被提交进行 DNA 分析，但实际上并没有 DNA 存在，这会导致分析这些拭子浪费时间和资源。本研究开发了一种简单、快速、基于 DNA 染色和荧光显微镜的筛选方法，用于指示拭子上是否有可用于生成图谱的 DNA。测试了十种不同类型的拭子，涵盖了主要使用的类型（泡沫、棉花和尼龙）。每个拭子都经过以下处理：不添加染料或 DNA、仅添加染料、添加已知 DNA 和添加染料和 DNA。使用的染料是 Diamond™Nucleic Acid Dye（DD），荧光显微镜使用配备蓝色 LED 光源（480nm）的数字显微镜进行激发，发射滤波器为 510nm。测试了两种类型的样品，一种是口腔拭子，另一种是志愿者接触区域采集的拭子，所有分析均重复进行三次。采集样本后在室温下保存，时间间隔为 0 天、7 天、14 天、21 天和 28 天，然后使用 DD 染色和荧光显微镜进行检测。结果发现七种拭子类型由于在未添加 DNA 或仅添加染料或 DNA 和染料混合物时检测到的荧光没有差异，因此不适合使用。三种拭子类型（黑色棉拭子、超细牙用涂药器和圆柱形牙用涂药器）被发现更适合用于采集 DNA。此外，染色的细胞物质保留其荧光长达 4 周，并且可以对保存了 4 周的含有细胞物质的拭子进行染色和可视化。此外，DD 不会影响 DNA 分析。这种筛选方法有可能成为法医实验室的常规步骤，可以节省处理无 DNA 拭子样本的成本。该技术快速、简便、廉价、非破坏性且安全。
