Conservation of evidence is crucial at a crime scene, most notably for blood or other biological samples. However, depending on the sample, traditional analytical methods are typically time consuming and destructive. Raman spectroscopy was first introduced in 1928 and since then has made an impact on forensic analysis as a valuable analytical tool, allowing for detection of trace amounts of a given material.1,2 Current developments in technology have allowed Raman spectrometers to become miniaturized and portable, which allows for real time analysis of substrates in the field. Unfortunately, Raman produces a weak signal, where only 1 per 10,000 photons are considered Raman active. The signal further suffers from masking by luminescence. 1 The drawbacks of standard Raman limit its usefulness in forensic analysis as the results will not necessarily hold up in court. More recently surface enhanced Raman spectroscopy (SERS) has been utilized, where excitation of the molecules is done on roughened metal substrates such as gold or silver. This method allows for an upsurge of Raman scattering up to 10 orders of magnitude while simultaneously quenching luminescence. 3
This spectroscopic technique allows for analysis of a variety of samples including paints, documents, explosives, drugs, fingerprints, and bodily fluids.1,2 The identification of blood is now possible up to a 1:100,000 dilution through the use of SERS.1 Building off the ability to provide a structural fingerprint of a sample such as blood, researchers have gone one step further by combining SERS with advanced statistical analyses, including partial least squares-discriminant analysis model (PLS-DA) and significant factor analysis (SFA).4,5 The combination of SERS and these statistical analyses enhance the analytic capabilities of Raman, allowing identification of species, race, and gender from a blood sample alone.4–7
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3. Haynes, C.L, McFarland, A.D., & Van Duyne, R. P. Anal. Chem. 77, 338A–346A (2005).
4. McLaughlin, G., Doty, K. C. & Lednev, I. K. Anal. Chem. 86, 11628–11633 (2014).
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6. Sikirzhytskaya, A., Sikirzhytski, V. & Lednev, I. K. Anal. Chem. 89, 1486–1492 (2017).
7. Mistek, E., Halámková, L., Doty, K. C., Muro, C. K. & Lednev, I. K. Anal. Chem. 88, 7453–7456 (2016).