15 demonstrated that a portable Raman spectrometer could be successfully used for this purpose. 14 also applied Raman spectroscopy and advanced statistical analysis to differentiate between human and animal blood. Our laboratory has demonstrated that Raman spectroscopy in combination with chemometrics allows for identification of species using bloodstain analysis 8, 11, 12, 13. They concluded that it was impossible to visually differentiate spectra of blood from different species. 10 was the first to report on the use of vibrational spectroscopy for discrimination between human and animal blood. In such cases, it is very advantageous to test any bloodstains on the suspect’s car to determine their origin.ĭe Wael et al. Discrimination between human and animal blood is especially important for hit-and-run cases when a suspect claims an incident involved an animal and not a human. The National Institute of Justice recently recommended that laboratories should consider going directly to DNA examination and perform serology only if necessary 9. Both presumptive and confirmatory assays are destructive in nature. Although some confirmatory tests can be conducted at a crime scene, the others require laboratory settings. Other species (e.g., ferret) can cause false positive results with some of these tests because of the hemoglobin composition, which is similar to that of human 7, 8. These tests are based on the reaction with hemoglobin and are specifically sensitive to human and higher primate bloods. Immunoassay tests, such as ABAcard® HemaTrace® and HemDirect Hemoglobin are routine human blood identification methods 6, 7. The two most common confirmatory assays for blood are the Teichmann and Takayama tests, which are both microcrystal tests 5. Confirmatory tests, which also use reactions between blood components and reagents, are more specific for identification of blood. However, there are other body fluids and substances that can react positively to these tests. These tests are based on reactions between blood components and a specific reagent. Preliminary tests are also known as presumptive or screening tests and can narrow the search field. An example protocol for the examination of blood involves physical examination of evidence, recording of evidence, preliminary tests, and confirmatory tests. Identification of blood can involve several analytical steps 5. Another significant development in forensic analysis is the introduction of advanced statistics that increase the reliability of the results, reduce the “human factor”, and provide information about the confidence interval, which is important for consideration of evidence in court 1, 2, 4.īloodstains found at crime scenes are very important evidence and one of the main sources of DNA. During the last decade, a variety of emerging analytical and bioanalytical methods have been developed for forensic serology, toxicology, and trace analysis 1, 2, 3. It is the role of analytical chemistry to detect and identify this material. Locard’s exchange principle says that “when two objects come into contact, material between them can be transferred” 1. Both validations showed excellent results demonstrating potential of the developed approach for nondestructive, rapid, and statistically confident discrimination between human and animal blood for forensic purposes.Īnalytical chemistry plays an important role in forensic science. The method was externally validated first using blood samples from new donors of species used in the training data set, and second using donors of new species that were not used to construct the model. A partial least squares discriminant analysis (PLSDA) was used for classification purposes and showed excellent performance in internal cross-validation (CV). Three other species (deer, elk, and ferret) were used for external validation. The following species were used to build statistical models for binary human–animal blood differentiation: cat, dog, rabbit, horse, cow, pig, opossum, and raccoon. Here, we report on the development of a nondestructive method that could potentially be applied at the scene for differentiation of human and animal blood using attenuated total reflection Fourier transform-infrared (ATR FT-IR) spectroscopy and statistical analysis. Current serological blood tests are destructive and often provide false positive results. Confirmation of the human origins of bloodstains is important in practical forensics. This field has been rapidly growing over the last several decades. Forensic chemistry is an important area of analytical chemistry.
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