Further developments in surface-enhanced Raman spectroscopy (SERS) for forensic trace body fluid detection
Reese, Traci R.
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It has been previously shown that SERS provides a rapid, confirmatory technique for the detection of blood, one of the most commonly found body fluids at a crime scene, from samples extracted with 1 µL of 50% acetic acid and placed on Au nanoparticle substrates developed by this laboratory. In recent results, the SERS spectra of blood extracted using a 50% acetic acid procedure is distinguished from 30 other reddish-brown stains (RBS) that do not contain blood, with 100% sensitivity and specificity using a partial least squares discriminant analysis (PLS-DA). A blind study was performed and 12 blinded samples were tested using the statistical method. All stains were identified as blood or non-blood with 100% accuracy. While peripheral blood and menstrual blood share many components, the complexity of menstrual blood is further enhanced by the addition of vaginal secretions. Further demonstrating SERS specificity, differential extraction procedures using water and acetic acid allow peripheral and menstrual blood to be distinguished. Given the sensitivity of SERS to identify bloodstains invisible to the naked eye, it is important to establish what limitations luminol might impose for SERS identification of bloodstains. SERS sensitivity allows blood diluted by a factor of at least 100 to be detected in the presence of undiluted luminol when using the acetic acid procedure. Current results demonstrate that the SERS detection limit is at least 103 diluted bloodstains when 1% luminol solutions, capable of producing the bright blue glow, are employed. In sexual assault cases, it may be necessary to identify the presence of semen prior to DNA analysis. Sexual assault cases may also require the identification of the presence of vaginal fluid in certain scenarios. A stain extraction method prior to SERS analysis was optimized for both semen and vaginal fluid by testing different extraction procedures with water and acetic acid. In semen, the acetic acid procedure was found to produce a signal intensity 4 times that of the water extraction procedure. Preliminary results show that for vaginal fluid, the water procedure was found to produce a SERS signal intensity more than 3 times that of the acetic acid procedure. Using differing solubilities of the chemical components of these body fluids, mixture deconvolution has been shown to be possible. The analysis of four swab types for SERS acquisition are compared in order to determine the optimal swab types for field collection of various trace body fluids. SERS analysis of trace body fluids for forensic work is a minimally destructive technique that can be applied for rapid and easy examination of evidence. The high sensitivity and specificity of SERS provides a robust spectroscopic technique for the rapid detection and identification of trace body fluids.