Comprehensive modeling of bloodstain aging by multivariate Raman spectral resolution with kinetics

Abstract

Blood, as a cardinal biological system, is a challenging target for biochemical characterization because of sample complexity and a lack of analytical approaches. To reveal and evaluate aging process of blood compositions is an unexplored issue in forensic analysis, which is useful to elucidate the details of a crime. Here we demonstrate a spectral deconvolution model of near-infrared Raman spectra of bloodstain to comprehensively describe the aging process based on the chemical mechanism, particularly the kinetics. The bloodstain spectra monitored over several months at different temperatures are decomposed into significant spectral components by multivariate calculation. The kinetic schemes of the spectral components are explored and subsequently incorporated into the developed algorithm for the optimal spectral resolution. Consequently, the index of bloodstain aging is proposed, which can be used under different experimental conditions. This work provides a novel perspective on the chemical mechanisms in bloodstain aging and facilitates forensic applications.

Rapid Detection of Amitriptyline in Dried Blood and Dried Saliva Samples with Surface-Enhanced Raman Spectroscopy

“…Figure 6 a shows the spectra of dried blood in the presence and absence of AMT over a period of 3 days. The intensities of the fluorescence background profile of some of the samples increased on day 3 ( Figure 6 e) [ 91 ]; however, despite the changes in the background, the linear range on all 3 days remained quite consistent ( Figure 6 f), and R 2 for the linear fit of the Raman spectra obtained on days 1, 2, and 3 was found to be 0.99, 0.97, and 0.98, respectively. This consistency in response to AMT, despite the slow changes in the matrix (i.e., blood), could also be due to the fact that AMT has a long lifetime and has scarcely photodegraded in the aqueous samples [ 92 ]; hence, AMT remains detectable in dried blood spots even after 3 days.…”

Toward a novel framework for bloodstains dating by Raman spectroscopy: How to avoid sample photodamage and subsampling errors

“…Part of the reason is that the ageing process of blood led to the increased background counts, which might have obscured observation of some small changes in incredibly complex signals that may be crucial for understanding the role of other possible pathways of the ex vivo degradation of bloodstains. A potential solution might be application of more advanced methods of mathematical modelling, such as multivariate curve resolution-alternative least squares (MCR-ALS) proposed by [45], which performs deconvolution of Raman spectra in order to enable identification of significant spectral components responsible for ageing process. Nevertheless, at this point of our study, it is important to comprehend that detailed exploration of ageing mechanisms was never the main motivation behind this research.…”

Raman Spectroscopy for the Time since Deposition Estimation of a Menstrual Bloodstain

“…Furthermore, the technique has numerous other advantages, such as sensitivity, rapidness, reproducibility, accuracy, portability, non-invasiveness, cost-effectiveness, and minimum sample preparation [ 17 ]. It is therefore not surprising that the methods of IR spectroscopy [ 20 , 21 ] and Raman spectroscopy [ 22 , 23 , 24 ] are strongly explored for TSD applications in recent studies. In a previous study, peripheral bloodstains were aged one week post-deposition, with continued research presenting an aging model for blood aged for two years [ 23 ].…”

“…The gradual transformation of individual forms of hemoglobin after bloodstain deposition is accompanied by a change in properties that can be detected using spectroscopic methods. Therefore, the oxyHb → metHb → Hc conversion is commonly used as a method of determining TSD for bloodstains [ 20 , 21 , 22 , 23 , 24 , 27 ].…”