The most important task in a criminal investigation is to detect and identify the recovered biological stains beyond reasonable scientific doubt and preserve the sample for further DNA analysis. In the light of this fact, many presumptive and confirmatory tests are routinely employed in the forensic laboratories to determine the type of body fluid. However, the currently used techniques are specific to one type of body fluid and hence it cannot be utilized to differentiate multiple body fluids. Moreover, these tests consume the samples in due process, and thus it becomes a great limitation especially considering the fact that samples are recovered in minute quantity in forensic cases. Therefore, such limitations necessitate the use of non-destructive techniques that can be applied simultaneously to all types of bodily fluids and allow sample preservation for further analysis. In the current work, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy has been used to circumvent the aforementioned limitations. The important factors which could influence the detection of blood such as the effect of substrates, washing/chemical treatment, ageing, and dilution limits on the analysis of blood have been analysed. In addition, blood discrimination from non-blood substance (biological and non-biological in nature) has also been studied. Chemometric technique that is PCA–LDA has been used to discriminate blood from other body fluids and it resulted in 100% accurate classification. Furthermore, blood and non-blood substances including fake blood have also been classified into separate clusters with a 100% accuracy, sensitivity, and specificity. All-inclusive, this preliminary study substantiates the potential application of ATR-FTIR spectroscopy for the non-destructive identification of blood traces in simulated forensic casework conditions with 0% rate of false classification.
Grass evidence often encountered at the crime scene, helps in establishing the primary as well as secondary crime scenes. Due to the limited quantity and intricate nature of samples, there is a need for fast, sensitive and reliable techniques for the effective analysis of this vital evidence. In the current study, an attempt is made to study the feasibility of ATR FT-IR in combination with chemometric tools for chemical characterization and species differentiation of grass stains. Ten different grass species belonging to three subfamilies, Panicoideae, Chlorodoidae, and Bambusoideae, were collected and analyzed by using the ATR FT-IR spectroscopy combined with the PLSR chemometric tool. Results showed a clear difference between samples of Panicoideae, Chlorodoidae, and Bambusoideae subfamilies, and between species of each subfamily. To analyse the performance of the classification model, a set of 10 unknown/blind samples (unknown to the analyst) were randomly selected from the training dataset and all unknown/blind samples were accurately assigned in their corresponding group. ATR FT-IR spectroscopy requires minimal sample preparation and can be successfully used as an eco-friendly, non-destructive, and reliable alternative to other existing methods.
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