Blood Species Identification for Forensic Purposes Using Raman Spectroscopy Combined with Advanced Statistical Analysis

Abstract

Forensic analysis has become one of the most growing areas of analytical chemistry in recent years. The ability to determine the species of origin of a body fluid sample is a very important and crucial part of a forensic investigation. We introduce here a new technique which utilizes a modern analytical method based on the combination of Raman spectroscopy and advanced statistics to analyze the composition of blood traces from different species. Near-infrared Raman spectroscopy (NIR) was used to analyze multiple dry samples of human, canine, and feline blood for the ultimate application to forensic species identification. All of the spectra were combined into a single data matrix, and the number of principle components that described the system was determined using multiple statistical methods such as significant factor analysis (SFA), principle component analysis (PCA), and several cross-validation methods. Of the six principle components that were determined to be present, the first three, which contributed over 90% to the spectral data of the system, were used to form a three-dimensional scores plot that clearly showed significant separation between the three groups of species. Ellipsoids representing a 99% confidence interval surrounding each species group showed no overlap. This technique using Raman spectroscopy is nondestructive and quick and can potentially be performed at the scene of a crime.

Discriminant Analysis of Raman Spectra for Body Fluid Identification for Forensic Purposes

“…Fluorescence and Raman spectroscopies are among the most promising nondestructive methods for confirmatory identification of body fluids [4][5][6][7][8][9][10][11][12]. The less sensitive Raman spectroscopy in comparison with fluorescence has higher selectivity and specificity to biochemical species and could potentially be useful in resolving mixtures of multiple body fluids with minimal sample preparation or manipulation [4][5][6][7][8][9][10][11]13]. We have recently demonstrated that the combination of Raman spectroscopy and advanced statistics can potentially discriminate human and animal blood traces [13,14].…”

“…The less sensitive Raman spectroscopy in comparison with fluorescence has higher selectivity and specificity to biochemical species and could potentially be useful in resolving mixtures of multiple body fluids with minimal sample preparation or manipulation [4][5][6][7][8][9][10][11]13]. We have recently demonstrated that the combination of Raman spectroscopy and advanced statistics can potentially discriminate human and animal blood traces [13,14]. Raman scattering is a powerful qualitative and quantitative analytical method based on a process where incident monochromatic photons interact with a sample to produce scattered photons with an energy distribution characteristic of molecular structure [15][16][17].…”

“…Advanced statistical methods allow for retrieving of reliable information from data sets that is not otherwise evident. We have been successful in developing and applying advanced statistical analysis of Raman spectra for biochemical [19][20][21][22][23][24][25][26][27] and forensic purposes [7][8][9]11,13].…”

Body Fluids and Spectroscopic Techniques in Forensics: A Perfect Match?

“…Although all blood stains were detected by these three techniques based on their characteristic spectral signal, the extreme similarity among the blood spectra of the three species frustrated the aim of distinguishing them, either by UV-Vis, IR or Raman spectroscopy. This challenging purpose regarding blood species discrimination was subsequently tackled by Lednev's group, by using Raman spectroscopy followed by chemometric analysis [28,29]. In this respect, chemometric analysis such as PCA enabled the discrimination of blood species based on slight spectral differences, differences that are hardly visible or even unnoticed for the naked eye but highly significant by chemometric procedures [28].…”

“…This challenging purpose regarding blood species discrimination was subsequently tackled by Lednev's group, by using Raman spectroscopy followed by chemometric analysis [28,29]. In this respect, chemometric analysis such as PCA enabled the discrimination of blood species based on slight spectral differences, differences that are hardly visible or even unnoticed for the naked eye but highly significant by chemometric procedures [28]. Thereby, the differentiation of blood from several species (up to 12) including human, dog, cat, cow, horse, pig and chicken, amongst others, has been successfully achieved [29].…”