PDF(Sci-hub)
Abstract：
Physicochemical property changes observed in a degrading bloodstain can be used to estimate its time since deposition (TSD) and provide a timestamp to the sample\'s age. Many of the time-dependent processes that occur as a bloodstain degrades, such as DNA fragmentation and changes in hemoglobin structure, also exhibit temperature-dependent behaviours. Previous studies have demonstrated that pairing high-resolution automated gel electrophoresis and visible absorbance spectroscopy could be used to quantify the rate of degradation of a bloodstain in relation to time and storage substrate. Our study investigates such trends with an added factor, extreme temperatures. Passive drip stains were stored in either microcentrifuge tubes or on FTA cards at either -20°C, 21°C or 40°C and tested over 11 time points spanning 15 days. For both storage substrates, the wavelength at maximum absorbance for the Soret band and the maximum absorbance of the Alpha band showed a negative trend over time suggesting that spectral shifts are informative for TSD estimates. The ratio of the maximum peak height for DNA fragments lengths of 500-1000 base pairs to 1000-5000 base pairs was the most informative DNA variable in relation to time for both substrates. Cross-validation suggested the appropriate fit of the models with the data and reasonable predictive ability. We integrated both DNA concentration and hemoglobin visible absorbance metrics using principal component analysis (PCA) into a single model. Adding the random effect of the donor to the PCA model accounted for a large portion of the variation as did storage method and temperature. Additionally, canonical correspondence showed that temperature corresponded differently to the response variables for FTA card and microcentrifuge tube samples, suggesting a substrate specific effect. This study confirms that pairing DNA concentration and hemoglobin\'s visible absorbance can provide insight on the effect of different environmental and storage conditions on bloodstain degradation. While the level of uncertainty surrounding TSD estimates still precludes its use in the field, this study provides a valuable framework that improves our understanding of variation surrounding TSD estimates, which will be critical to any eventual application.
摘要：
在降解的血迹中观察到的物理化学性质变化可用于估计其沉积时间（TSD），并提供样品年龄的时间戳。许多随着血迹降解而发生的时间依赖性过程，比如DNA片段化和血红蛋白结构的改变,还表现出温度依赖性行为。先前的研究表明，配对高分辨率自动凝胶电泳和可见吸收光谱可用于量化血迹相对于时间和储存基质的降解速率。我们的研究调查了这种趋势，增加了一个因素，极端温度。被动滴注污渍储存在微量离心管中或在-20°C的FTA卡上，21°C或40°C,并在跨越15天的11个时间点进行测试。对于两种存储基板，Soret谱带的最大吸光度波长和Alpha谱带的最大吸光度随时间呈负趋势,提示光谱偏移可为TSD估计提供信息.长度为500-1000个碱基对的DNA片段的最大峰高与1000-5000个碱基对的比率是两种底物相对于时间的最有用的DNA变量。交叉验证表明模型与数据的适当拟合和合理的预测能力。我们使用主成分分析（PCA）将DNA浓度和血红蛋白可见吸光度指标整合到单个模型中。将供体的随机效应添加到PCA模型中占了很大一部分的变化，储存方法和温度也是如此。此外,规范对应表明，温度对应于FTA卡和微量离心管样品的响应变量不同，表明了底物的特定效应。这项研究证实，配对DNA浓度和血红蛋白的可见吸光度可以提供不同环境和储存条件对血迹降解的影响。虽然围绕TSD估计的不确定性水平仍然无法将其用于该领域，这项研究提供了一个有价值的框架，提高了我们对TSD估计变化的理解，这对任何最终应用程序都至关重要。
