Portable Spectroscopy and Forensic Analysis: Trends and Emerging Technologies

Spectroscopy plays a crucial role in forensic analysis by enabling the identification and characterization of substances at crime scenes. Forensic analysis is the scientific detection, evaluation, and examination compiled from crime scenes to support the investigation of legal cases (1).

Different spectroscopy techniques, such as infrared (IR), ultraviolet-visible (UV-vis), and Raman spectroscopy, are employed depending on the nature of the material being analyzed (2). IR spectroscopy is particularly useful for identifying organic compounds by examining the vibrational modes of molecules. UV-vis spectroscopy is often applied in cases involving colored substances, such as inks or dyes, to analyze their composition (2,3). Raman spectroscopy allows for rapid, non-invasive identification of both organic and inorganic substances, often complementing other forms of chemical analysis. The introduction of portable Raman spectrometers has also allowed Raman spectroscopy to become a technique of choice because it requires no sample preparation (4).

Forensic police investigator collecting evidence at the crime scene by the river in nature at night selective focus on police line tape. | Image Credit: © Miljan Živković - stock.adobe.com

The global portable spectrometer market has exploded over the past few years and is expected to continue to grow as the demand for these instruments continues to increase. From a market size valued at $1,675.7 million in 2020, the portable spectrometer market is expected to reach $4,065.7 million by 2030, registering a compound annual gross rate (CAGR) of 9.1% from 2021 to 2030 (5).

The portability of instrumentation has resulted in massive changes in how forensic investigations are conducted. For example, handheld instrumentation allows for on-site analysis without transporting samples to a laboratory. As a result, handheld instrumentation has helped reduce the cost and time of forensic investigations, allowing law enforcement agencies to solve cases quicker. This development has been important for forensic investigations because many spectroscopic techniques are used in this field. Kabrena E. Rodda, Ph.D., a Fellow of the American Chemical Society and a research line manager at a private nonprofit science and technology development company, said that a variety of detection modalities are used to investigate crime scenes.

“Many involve handheld detectors that utilize a variety of spectroscopic techniques including Raman, ultraviolet-visible (UV-vis), and infrared (IR), as well as commonly used tools such as UV lamps, which can help investigators find and collect samples of bodily fluids, gunshot residue, fibers, paint chips, and many other types of trace evidence,” Rodda said.

Handheld and portable instrumentation now possess similar capabilities to their benchtop counterparts, which has made them become more valuable in forensic investigations. Brooke Kammrath, a Professor in the Henry C. Lee College of Criminal Justice and Forensic Sciences at the University of New Haven and the Executive Director of the Henry C. Lee Institute of Forensic Science, told Spectroscopy that portable spectrometers contain the capabilities forensic analysts like in their benchtop counterparts. The issue though, Kammrath said, is that portable spectrometers currently are not able to analyze all samples forensic analysts may encounter in their work.

“Portable spectroscopic technologies have the exciting potential to bring powerful science to the scene. Some portable spectrometers are incredibly advanced with capabilities on par with their benchtop counterparts, (for example, FT-IR spectrometers), whereas others are relatively new technologies that need additional research and real-world validations to understand their capabilities and limitations. Ultimately, Star Trek’s tricorder is still far from reality, and there is no single portable spectrometer able to analyze all samples,” said Kammrath (6).

The Limitations of Spectroscopic Instrumentation

Despite the advancements made in spectroscopic instrumentation in forensic investigations, limitations remain in the instrumentation that force analysts to make tough choices when applying these instruments in a crime scene investigation.

“The biggest challenges with conducting a forensic investigation at a crime scene are the natural tradeoff between selectivity (differentiating between several different components in a sample), specificity (ability to detect a specific substance in a sample), and sensitivity (ability to detect very small amounts of a substance in a sample),” Rodda said. “Many handheld detectors may be sensitive, but they lack specificity and/or selectivity, which may cause many false positives (indicating a detection when the substance of interest is not present) or false negatives (indicating a specific substance of concern is not present when it actually is). This is why findings from initial crime scene investigations are best confirmed by more time-intensive sample analysis in a laboratory – but such analyses take much more time and cost more to complete.”

Therefore, one of the first issues forensic analysts encounter at the crime scene is how to balance finding the right selectivity, specificity, and sensitivity for their instrument while conducting their investigation. Ultimately, the analyst will have to decide what is more important at the stage of the investigation.

“It comes down to whether you need an answer quickly (in which case you will most likely have to sacrifice selectivity and specificity, leading to more false positives or false negatives) or whether you have more time (in which case you can perform measurements that take more time but which are able to provide much more accurate and reliable results—meaning fewer false positives and false negatives),” Rodda said.

Forensic analysts have been creative in mitigating these challenges. For example, Rodda said that forensic analysts sometimes do a screening to remove samples that do not contain any analytes of interest. Although this method does result in many false positives, it is often good at removing samples that are not worth the time to study further.

Although this screening process cannot reduce the time that confirmation analysis requires in the second step, Rodda said, it still allows analysts to feel more confident that the samples undergoing this process will turn up worthwhile results.

“While confirmation techniques take more time (and are more expensive), since they are performed on a subset of the total number of samples and the screening results indicate an analyte of interest is present, lab managers can have a higher degree of confidence that samples sent for confirmation warrant the additional cost per sample,” Rodda said.

Emerging Technologies

The introduction of new technologies and machine learning (ML) applications has opened avenues for novel methods to be developed that attempt to address some of these concerns. For example, a research team from the Massachusetts Institute of Technology introduced a ML package called Chemprop, which uses deep learning tools to predict molecular properties, which can help forensic analysts detect chemical compounds that are new and/or when standard reference materials do not exist (7). There have also been positive developments in using a combination of high-resolution mass spectrometry (HRMS) and ion mobility spectrometry (IMS) to identify nitazenes, which is a new class of novel synthetic opioids (8). As a result, these developments show that researchers are finding new methods and techniques to meet the current challenges in criminal investigations.

Ultimately, the biggest challenge heading into the future for forensic analysis is the selectivity, specificity, and selectivity challenge. Solving this challenge will be critical toward obtaining better results in criminal investigations and handling more criminal cases.

“We need to continue to advance capabilities to provide fast results which are also sensitive, selective, and specific enough to provide reliable results,” Rodda said. “A fast test is not worth performing if the results it yields leave you scratching your head.”

References

1. Shehova, A. What is Forensic Analysis and Why is it Important for the Security of Your Infrastructure. Virtual Metric. Available at: https://www.virtualmetric.com/blog/forensic-analysis-and-the-security-of-infrastructure (accessed 2024-06-19).
2. Wetzel, W. Spectroscopy Announces Upcoming Content Series on Forensic Analysis. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/spectroscopy-announces-upcoming-content-series-on-forensic-analysis (accessed 2024-09-11).
3. Kaveti, B. What Spectroscopy Techniques are Most Useful in Forensics? Azo Optics. Available at: https://www.azooptics.com/Article.aspx?ArticleID=2456 (accessed 2024-06-19).
4. (4)George, N.; Singh, H.; Jotaniya, R.; Pandya, S. R. Raman Spectroscopy for the Determination of Forensically Important Bio-fluids. Forensic Sci. Int. 2022, 340, 111441. DOI: 10.1016/j.forsciint.2022.111441
5. Chasse, J. Portable Spectrometer Market to Grow Past $4 Million by 2030. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/portable-spectrometer-market-to-grow-past-4-million-by-2030 (accessed 2024-10-04).
6. Wetzel, W. The Future of Forensic Analysis: An Interview with Brooke Kammrath. The Future of Forensic Analysis. 2024, ASAP.
7. Heid, E.; Greenman, K. P.; Chung, Y.; et al. Chemprop: A Machine Learning Package for Chemical Property Prediction. J. Chem. Inf. Model. 2024, 64 (1), 9–17. DOI: 10.1021/acs.jcim.3c01250
8. Hollerbach, A. L.; Lin, V. S.; Ewing, R. G.; et al. Elucidating the Gas-Phase Behavior of Nitazene Analog Protomers Using Structures for Lossless Ion Manipulations Ion Mobility-Orbitrap Mass Spectrometry. J. Am. Soc. Mass Spectrom. 2024, 35 (7), 1609–1621. DOI: 10.1021/jasms.4c00200