Investigating the Effect of Ageing and Substrate Variation on the Raman Spectrum of Equine Blood
Blood is one of the most common and useful evidence types found at the crime scene. Blood can indicate the number of suspects involved, the weapon used, the series of events, and can be used to generate DNA profiles. However, in some circumstances it can be difficult to identify blood on various substrates. Additionally other substances (such as paint and foodstuff) can be mistaken for blood. Current presumptive and confirmatory tests for blood used in forensic science (such as Luminol and Crystalline tests) have certain disadvantages including false positives and invasive testing. Raman spectroscopy is a method of non-invasive, confirmatory testing for blood and (with the recent development of handheld spectrometers) confirmation of blood at the crime scene is now possible The aim of this research is to investigate the effect of ageing and substrate variation on the Raman spectrum of Equine blood. The main focus will be on the possible effects on the main peak intensities corresponding to blood. This paper will also discuss the reliability of Raman spectroscopy to identify blood in conditions to those similar to the crime scene environment. Through analysis of spectra collected using Raman spectroscopy it was possible to demonstrate that the main peaks corresponding to blood undergo changes in intensity over time. The general change was an increase in intensity over time which did not correspond to the expectations of the study. However, decreases in intensity were seen at peaks 1587cm-1 and 1640cm-1 over time which did correspond to the expectations of the study and did correspond to haemoglobin degradation. Additionally, using Raman spectroscopy it was possible to demonstrate that the main peaks corresponding to blood undergo peak intensity fluctuations across various substrates. Initially, peak intensities varied greatly with each other and then decreased over time. The most significant decrease in intensity was seen at peaks 1587cm-1 and 1640cm-1 which correspond to haemoglobin degradation. Bought Equine (horse) blood was deposited on 6 substrates used for analysis: crystalline silicon (standard), a condom, brown leather, a ceramic tile, laminate flooring and blue denim. These substrates were chosen to represent similar substrates which blood may come into contact with at the crime scene. 3 droplets on each substrate were then analysed via Raman spectroscopy over a period of three months at time periods of: ≤1hr, 2hrs, 5hrs, 24hrs, 1 week, 2 weeks, 1 month (28days), 2 months (56 days) and 3 months (84 days). This research combines both ageing and substrate studies where previous research has only analysed the two separately. This research will also provide evidence for the use of Raman spectroscopy in a forensic context, specifically, when analysing blood at different stages of ageing and on different substrates.
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