Institute of Chemistry, University of Silesia in Katowice, Szkolna 9, 40-007, Katowice, Poland.
Department of Chemistry, University of Torino, Via P. Giuria 7, 10125, Torino, Italy.
Talanta. 2020 Mar 1;209:120565. doi: 10.1016/j.talanta.2019.120565. Epub 2019 Nov 15.
Answers to questions about the time of bloodstains formation are often essential to unravel the sequence of events behind criminal acts. Unfortunately, the relevance of preserved evidence to the committed offence usually cannot be verified, because forensic experts are still incapable of providing an accurate estimate of the bloodstains' age. An antidote to this impediment might be substituting the classical dating approach - founded on the application of calibration models - by the comparison problem addressed using likelihood ratio tests. The key aspect of this concept involves comparing the evidential data with results characterizing reference bloodstains, formed during the process of supervised ageing so as to reproduce the evidence. Since this comparison requires data that conveys information inherent to changes accompanying the process of blood decomposition, this study provided a Raman-based procedure, designated for probing into the chemistry of ageing bloodstains. To circumvent limitations experienced with single-point measurements - the risk of laser-induced degradation of hemoglobin and subsampling errors - the rotating mode of spectral acquisition was introduced. In order to verify the performance of this novel sampling method, obtained spectra were confronted with those acquired during conventional static measurements. The visual comparison was followed by analysis of data structure using regularized MANOVA, which boosted the variance between differently-aged samples while minimizing the variance observed for bloodstains deposited at the same time. Studies of relation between these variances demonstrated the superiority of novel procedure, as it provided Raman signatures that enabled a better distinction between differently-aged bloodstains.
关于血斑形成时间的问题的答案通常对于揭示犯罪行为背后的事件顺序至关重要。不幸的是，由于法医专家仍然无法准确估计血斑的年龄，因此保留证据与犯罪行为的相关性通常无法得到验证。解决这一障碍的一种方法可能是用似然比检验解决的比较问题来替代基于校准模型应用的经典定年方法。这个概念的关键方面涉及将证据数据与在监督老化过程中形成的参考血斑的特征结果进行比较，以重现证据。由于这种比较需要携带伴随血液分解过程的变化的固有信息的数据，因此本研究提供了一种基于拉曼的方法，旨在探测老化血斑的化学性质。为了避免单点测量所经历的限制 - 血红蛋白激光诱导降解和抽样误差的风险 - 引入了旋转光谱采集模式。为了验证这种新型采样方法的性能，将获得的光谱与在传统静态测量过程中获得的光谱进行比较。进行了目视比较，然后使用正则化 MANOVA 分析数据结构，该方法增强了不同老化样品之间的方差，同时最小化了在同一时间沉积的血斑的方差。对这些方差之间的关系的研究表明了新方法的优越性，因为它提供了拉曼特征，可以更好地区分不同年龄的血斑。
