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Surface-enhanced Raman spectroscopy for forensic analysis of human semen

机译：表面增强拉曼光谱法用于人精液的法医分析

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摘要

Identification of an unknown stain encountered at a crime scene, especially where the context of the case does not provide an indication to the identity of the stain, currently requires a number of time consuming and costly presumptive and confirmatory tests to be performed. Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopic method that could allow crime scene analysts to identify unknown stains rapidly both in the laboratory and in the field. The SERS technique utilizes a laser, which interacts with molecules applied to a gold nanoparticle chip (SERS substrate) that enhances the normal Raman signal, producing a shift in energy characteristic of the vibrational modes present. Therefore, the light scattering spectrum obtained provides the analyst with a unique spectral fingerprint of the molecular components of the sample. The advantages of this SERS based method include its high sensitivity, speed, non-destructive nature, ease-of-use, minimal sample preparation requirement, portability, and multiplexing capabilities.;In contrast to conventional Raman spectroscopy, SERS offers higher sensitivity resulting in small sample volumes (approximately 1 muL or less) being required for sample identification and the ability to process dilute solutions. This allows for the remaining sample to be used for other forensic tests, making the technique an ideal analytical method for use at a crime scene.;It is hypothesized that SERS can be coupled with multivariate statistical methods, such as principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) to be established as a confirmatory technique in the forensic analysis of human body fluids. It was concluded that semen produces a spectral pattern that is consistent and readily distinct from blood, saliva, urine and vaginal fluid. In addition, this investigation identified and characterized semen from four donors, utilizing liquid semen as well as semen stains on cotton swatches and glass cover slips.;Reproducibility was established by analyzing three separate SERS chips for every sample and/or solution. Ten spectra of each chip were obtained, averaged, and then compared to one another. A protocol was designed for the extraction of dried semen stains on cotton swatches and application to a SERS chip. Different extraction conditions were performed, varying both the volume of water used and the time the cutting remained submerged in the water, resulting in optimal signal from 5 muL of water for 5 minutes. Additional parameters including analysis of the perimeter of the stain and the use of saline as an extractant were examined. A second protocol for the extraction of dried semen stains from a glass cover slip was designed and tested, utilizing 1 muL of water. All experimental spectra were subjected to PCA for comparison with neat semen, and determined to be consistent. Additionally, a mixture of semen and vaginal fluid was evaluated. Visual inspection and PCA of the resulting spectra demonstrated that the mixture was a combination of both body fluids. Such samples are of particular importance in sexual assault cases.;In summary, this preliminary study of the identification of semen using SERS demonstrates the potential for the method to be used as an investigative tool for the detection of trace amounts of human body fluids at crime scenes and within forensic laboratories. Not only is semen differentiable from other body fluids, but it is also capable of being extracted from stains and successfully identified by SERS.
机译：识别在犯罪现场遇到的未知污渍，尤其是在案件背景无法提供对污渍身份的指示的情况下，当前需要执行许多耗时且昂贵的推定和确认测试。表面增强拉曼光谱法（SERS）是一种振动光谱法，可让犯罪现场分析人员在实验室和现场快速识别未知的污渍。 SERS技术利用激光，该激光与施加到金纳米颗粒芯片（SERS基板）上的分子相互作用，从而增强正常的拉曼信号，从而产生所存在振动模式的能量特征偏移。因此，获得的光散射光谱为分析人员提供了样品分子成分的独特光谱指纹。这种基于SERS的方法的优势包括其高灵敏度，速度快，无损性质，易用性，最小的样品制备要求，便携性和多路复用能力。与传统的拉曼光谱法相比，SERS具有更高的灵敏度，从而样品鉴定和处理稀溶液的能力需要小样品量（大约1μL或更少）。这使得剩余的样品可以用于其他法医测试，从而使该技术成为在犯罪现场使用的理想分析方法。;假设SERS可以与多元统计方法结合使用，例如主成分分析（PCA）偏最小二乘判别分析（PLS-DA）将被建立为人体液体法医分析的一种验证技术。结论是精液产生的光谱模式是一致的，并且很容易与血液，唾液，尿液和阴道液区分开。此外，这项研究利用液体精液以及棉样和玻璃盖玻片上的精液污渍，鉴定和鉴定了来自四个供体的精液。通过对每种样品和/或溶液分析三个单独的SERS芯片，建立了可重复性。获得每个芯片的十个光谱，取平均值，然后相互比较。设计了一种协议，用于提取棉样上的干燥精液污渍并将其应用于SERS芯片。进行了不同的提取条件，同时改变了用水量和切削液浸入水中的时间，从而从5μL水中提取了5分钟的最佳信号。还检查了其他参数，包括分析污渍的周长以及使用盐水作为萃取剂。设计并测试了使用1μL水从玻璃盖玻片上提取干燥精液污渍的第二种方法。所有实验光谱均经过PCA与纯精液比较，并确定是一致的。另外，评估了精液和阴道液的混合物。目视检查和所得光谱的PCA表明混合物是两种体液的混合物。此类样品在性侵犯案件中尤为重要。总之，对使用SERS鉴定精液的初步研究表明，该方法有可能用作侦查犯罪现场微量人体液的调查工具。现场和法医实验室内。精液不仅可以与其他体液区分开，而且还可以从污渍中提取并通过SERS成功鉴定。

著录项

  • 作者

    Irvine, Jessica.;

  • 作者单位

    Boston University.;

  • 授予单位 Boston University.;
  • 学科 Analytical chemistry.;Criminology.
  • 学位 M.S.
  • 年度 2015
  • 页码 80 p.
  • 总页数 80
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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