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Raman spectroscopy is a well-established technique in the forensics field, particularly in criminal forensics. The technique has benefits over alternative techniques, particularly in its non-destructive nature, speed, and accuracy, which has helped develop its use in several forensic applications. Due to the importance of accuracy when conducting forensic analyses given that the data may be presented in court, as well as the benefits of Raman spectroscopy in forensics, scientists continue to work on improving the technique and exploring more applications of the method. Here, we discuss the current uses and recent developments of using Raman spectroscopy in forensic applications.
The Principles of Raman Spectroscopy
Raman spectroscopy is an optical analytical method that measures the vibrational energy of a sample via scattered light. The technique provides chemical and structural information about the sample and can also be used to identify unknown substances through what is known as the Raman ‘fingerprint’.
During Raman spectroscopy, light is exposed to a source and its Raman scattering is detected. It is based on the principle that when light is scattered by a molecule, the photon’s oscillating electromagnetic field polarizes the molecule’s electron, leaving the molecule in a higher state of energy than before it interacted with the photon. Because this state is relatively short-term, it is known as a virtual state. After a brief time, almost immediately, the photon becomes released as scattered light. This pattern of scattered light can inform scientists about the properties of the molecule and help to identify it.
This ability to use Raman scattering to identify samples has made it invaluable to the field of forensic science. In addition, Raman spectroscopy is a non-destructive analytical method, which is important in forensics, particularly in criminal forensics where preservation of evidence is vitally important. This has helped Raman spectroscopy thrive in forensics, above alternative methods.
Current Applications of Raman Spectroscopy in Forensics
Raman spectroscopy has been developed to analyze a wide range of forensic samples. It can investigate blood and other bodily fluids such as saliva, semen, sweat, tears, and vaginal secretion. An amended version of Raman spectroscopy, surface-enhanced Raman scattering (SERS), has proven to be reliable in analyzing fibers and other physical evidence commonly left behind at a crime scene, such as dyes, paints, fibers, textiles, lipsticks, and shoe polish.
Raman spectroscopy can also be used to detect fraudulent documents. Due to its highly sensitive nature, the technique can identify when different inks have been used to change a document and can indicate where changes have been made. Finally, Raman spectroscopy is also currently used to examine gunshot residue, helping to identify the weapon used in a crime and to detect traces of illicit drugs.
Recent Developments in Raman Spectroscopy in Forensics
Current research into the use of Raman spectroscopy in forensic applications focuses on validating the current uses (discussed above). Recent reviews have confirmed, for instance, the use of Raman spectroscopy in forensic serology and forensic phenotype profiling has recently been validated. Additionally, there is a wide body of research that has recently confirmed the efficacy of Raman spectroscopy in analyzing other types of forensic evidence, such as controlled substances, counterfeit pharmaceuticals, explosives, gunshot residue, hair, fibers, lipstick, paint, and nail polish. There have also been recent studies validating the use of Raman spectroscopy in chemometrics, toxicology, and forensic anthropology. These studies have helped to further cement Raman spectroscopy’s respected place within the field of forensics.
Recent research has also focused on exploring how the capabilities of Raman spectroscopy in forensics can be developed. For example, a 2019 study demonstrated that the technique can be used alongside random forest statistics to differentiate between environmental interferences and bloodstains, overcoming the limitation of the genetic algorithm in differentiating numerous environmental interferences.
Further to this, another 2019 study showed that Raman spectroscopy can be developed to differentiate between samples of bodily fluids left by smokers and non-smokers, demonstrating another application of the technique in forensics which may be useful in helping to identify suspects or victims.
A 2020 study combined Raman spectroscopy with chemometrics as a non-destructive and rapid method capable of identifying semen traces. Another 2020 study assessed the use of a newly established handheld Raman spectroscopy device in detecting illicit drugs (cocaine), demonstrating the potential to investigate samples with Raman spectroscopy in the field without the need to transport evidence.
Future Directions of Raman Spectroscopy in Forensics
Because evidence analyzed with Raman spectroscopy in forensic applications is often presented in court, scientists continue to work on both improving the technique and exploring its capabilities. Currently, a growing body of research is dedicated to confirming the accuracy and reliability of the technique in already established applications. There is much research exploring new uses of the method, and we can expect continued developments in the field, with more applications of Raman spectroscopy in forensics emerging in the coming years.
References and Further Reading
Al‐Hetlani, E., Halámková, L., Amin, M. and Lednev, I., 2019. Differentiating smokers and nonsmokers based on Raman spectroscopy of oral fluid and advanced statistics for forensic applications. Journal of Biophotonics, 13(3). https://onlinelibrary.wiley.com/doi/abs/10.1002/jbio.201960123
Casey, T., Mistek, E., Halámková, L. and Lednev, I., 2020. Raman spectroscopy for forensic semen identification: Method validation vs. environmental interferences. Vibrational Spectroscopy, 109, p.103065. https://www.sciencedirect.com/science/article/abs/pii/S0924203120300680
Doty, K. and Lednev, I., 2018. Raman spectroscopy for forensic purposes: Recent applications for serology and gunshot residue analysis. TrAC Trends in Analytical Chemistry, 103, pp.215-222. https://www.sciencedirect.com/science/article/abs/pii/S0165993617304314
Kranenburg, R., Verduin, J., Ridder, R., Weesepoel, Y., Alewijn, M., Heerschop, M., Keizers, P., Esch, A. and Asten, A., 2021. Performance evaluation of handheld Raman spectroscopy for cocaine detection in forensic case samples. Drug Testing and Analysis,. https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/full/10.1002/dta.2993
Muehlethaler, C., Leona, M. and Lombardi, J. (2015). Review of Surface Enhanced Raman Scattering Applications in Forensic Science. Analytical Chemistry, 88(1), pp.152-169. https://pubs.acs.org/doi/abs/10.1021/acs.analchem.5b04131
Rosenblatt, R., Halámková, L., Doty, K., de Oliveira, E. and Lednev, I., 2019. Raman spectroscopy for forensic bloodstain identification: Method validation vs. environmental interferences. Forensic Chemistry, 16, p.100175. https://www.sciencedirect.com/science/article/abs/pii/S2468170919300724