Journal of Forensic Pathology

Application of New Raman Spectroscopic Techniques in Forensic Science

George Wilson^{* *}Correspondence: George Wilson, Department of Forensic Pathology, Freie University of Berlin, Berlin, Germany, Email:

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Introduction

Raman spectroscopy has grown in popularity in the realm of forensic investigation and has been designated as a category a method by the Scientific Working Group for the Analysis of Seized Drugs (SWGDRUG) due to its high potential level of selectivity through structural information. Raman spectroscopy is a nondestructive, non-invasive technique that can be used to analyse even the smallest sample with very little sample preparation [1]. Water does not exhibit strong signals in Raman spectroscopy, despite having powerful IR signals that can dwarf those of genuine analytes. Because water doesn't obscure analyte peaks in aqueous solutions, it is easier and more desired to examine various types of forensic evidence that contains water or moisture. They are perfect for on-site forensic investigation because there are now many portable Raman or handheld Raman spectrometers available [2].

Literature Review

Conventional/normal Raman signals are innately weak because very few photons from the light source are dispersed, and only one in ten million of those scattered photons engage in Raman scattering. This is typically not a barrier to bulk analysis, and even when portable/handheld devices are used, conventional Raman spectroscopy approaches have been found to be adequate for such samples. Analyzing trace evidence, which calls for extremely sensitive detection, is difficult, nevertheless. To achieve high sensitivity, techniques have been devised to produce substantially stronger Raman signals. Surface Enhanced Raman Spectroscopy is one of them (SERS) [3]. Even when SERS is used, fluorescence from some samples not just from the analytic but also frequently from contaminants or packaging materials can significantly obscure the analyses Raman peaks. Resonance Raman spectroscopy, using a longer wavelength light source, like a 1064 nm Near Infrared (NIR) laser, and other techniques can help to some extent to reduce this issue. These techniques do, however, have certain inherent drawbacks. For instance, when NIR light sources are used, Raman signals may be substantially weaker since scattering is inversely proportional to the 4th power of the input light's wavelength (to minimise fluorescence interference). In order to overcome fluorescence interference in the Raman examination of some forensic evidence, forensic experts have lately begun to use a novel technique called Shifted Excitation Raman Difference Spectroscopy (SERDS), at least through some proof of concept experiments. For surface analysis, the traditional backscattering Raman spectroscopy method is appropriate [4]. Although standard confocal Raman microscopy can be utilised to investigate subsurface layers if top layers are transparent, employing it to directly analyse a subsurface material via a turbid surface layer can be very difficult. No matter whether the surface layer is clear or not, Spatially Offset Raman Spectroscopy (SORS) has been created to extract subsurface Raman data, finding use in the field of forensic research. A strong and useful technique in forensic analysis is conventional Raman spectroscopy, commonly referred to as regular or ordinary Raman spectroscopy. It has been demonstrated to be able to discern between a variety of physiological fluids, as well as gender, race, and chronic age differences in blood samples. Semen samples of different races can also be distinguished by it. The forensic analysis of paints, ink/questionable documents, fibers, gunshot residue, and other evidence has been done using Raman spectroscopy. Using a 785 nm laser as the excitation source, conventional Raman spectroscopy was employed to separate several types of cocaine that had been confiscated. Additionally, it was discovered to be more accurate than FT-IR at detecting benzoic acid and inorganic adulterants in cocaine seizures. In preparation for use in actual forensic analysis, Raman spectroscopy techniques have also been developed to locate and measure cocaine obfuscated in food matrices and a cocaine analogue impregnated in textile. In a recent investigation, the Raman spectra of 21 phenethylamines were obtained with the aid of statistical methods, it has been demonstrated that traditional Raman spectroscopy can distinguish between all varieties of regioisomers and structural analogues, even homologs, among these phenethylamines. A very high % (95%) of 59 confiscated phenethylamine samples was accurately identified with only minimal sample preparation, demonstrating the promise of this non-destructive technology in the forensic field investigation.

Discussion

A thorough study of traditional Raman spectroscopy in forensic analysis has been done. The application of SERS, SERDS, and SORS in forensic research and investigation will be the main topic of this paper. Despite the fact that Raman scattering is typically very weak, it has been discovered that many molecules that adsorb on particular rough metal surfaces, particularly metal nanoparticles, as well as other nanostructures or porous structures, greatly enhance Raman scattering signals by up to 1011 times. Surface Enhanced Raman Spectroscopy was born as a result of this (SERS). It is hardly surprising that the field of forensic science has adopted this technique for the more delicate examination of evidence, particularly that involving banned chemicals [5].

After micro extraction using commercially available colloidal silver nanoparticles and the aggregating agent KBr, scientists at a forensic science laboratory run by the US FDA developed a SERS method using handheld Raman spectrometers for quick and sensitive detection (as low as 100 mg/mL) of fentanyl and other opioids in low dosage pills. The majority of the time, a 10% aqueous methanol solution was the ideal solvent for this type of analysis because it was more effective than pure water at dissolving Active Pharmaceutical Ingredients (APIs) or just the active component. Additionally, compared to utilising pure methanol, it provided less methanol interference in SERS. The API peaks were far more intense than the methanol peaks after the addition of KBr, whereas the methanol peaks looked to have significantly decreased, if not completely disappeared. The nanoparticles then gathered to form SERS hot spots. Fentanyl was one of the opioids examined in the aforementioned SERS study; however, due to its extraordinarily high potency and toxicity, it often only makes up a small portion of relevant street narcotics. It calls for the development of highly sensitive detection techniques, particularly in the field. Although there were slight variations in shift wavenumbers coming from the same vibration modes, the normal Raman and SERS spectra of fentanyl were found to be relatively similar. The strongest peaks in the fentanyl SERS Raman spectrum appeared at 1002 cm^-1 and 1030 cm^-1, which are connected to various phenyl ring vibration modes. Similar findings were made in other SERS fentanyl experiments utilising gold or silver nanoparticles. In the SERS spectrum, the amide carbonyl peak at 1647 cm, which is present in the regular Raman spectrum, was not present. Based on these findings, it was believed that the amide carbonyl oxygen was coordinated with the metal nanoparticle surface and that the aromatic ring of fentanyl was adsorbed perpendicular to the metal nanoparticle surface. The suspect tablets were examined using this technique. For instance, a blue tablet in issue was seized and examined using the two hand held Raman spectrometers stated above: A progeny instrument with a 1064 nm near IR excitation laser and a TruScan RM device with a 785 nm excitation laser. The tablet core's conventional/normal Raman spectra, which was measured with the 785 nm excitation and yielded little information due to excessive fluorescence background and other interference. Although the use of the 1064 nm excitation resolved the fluorescence interference problem, it only provided a spectrum that was consistent with mannitol, which was likely used as an excipient in the pill and didn't exhibit any fentanyl peaks, according to a library search. Both instruments typical Raman spectra of the 10% methanol extract were dominated by methanol signals, not fentanyl peaks or other flag peaks associated with other restricted compounds. At least in this instance, conventional/normal Raman spectroscopy was useless and could have produced inaccurate results [6].

Conclusion

However, when the extract was combined with a silver nanoparticle colloid for SERS experiments, both instruments obtained spectra with recognisable fentanyl peaks. More importantly, when KBr was added to the extract silver nanoparticle colloid mixture, fentanyl peaks were significantly enhanced in comparison to those from other species. This enhancement was particularly noticeable between the fentanyl peak at 1002 cm and the methanol peak at 1019 cm, which was very similar to the spectra of standard fentanyl acquired under the same conditions with only a few very small differences. Due to the tiny dosage of this tablet, it appears that conventional/normal Raman could not determine whether it included fentanyl, whereas SERS did, particularly after hotspots were created by the addition of the aggregating agent KBr.

References

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