The Raman technique is gaining widespread acceptance as an investigative tool for forensic applications. This article focuses on the use of portable and handheld Raman spectroscopy in the field of forensic science and illustrates it with real-world examples.
The benefits of Raman spectroscopy are well recognized for the molecular identification of unknown molecular compounds and as a result the technique is being used routinely in applications areas such as pharmaceutical manufacturing (1), raw material verification (2), detection of counterfeit drugs (3), medical diagnostics (4), characterization of polymers (5), and the quality control of food products (6). However, more recently the technique is gaining widespread acceptance as an investigative tool in the areas of forensic science and homeland security (7,8). On-board spectral libraries and intelligent decision-making software make Raman spectroscopy ideally suited to help law enforcement agencies better understand the source and nature of illicit materials. Today's Raman instrumentation is faster, more rugged, and less expensive, and the advances in component miniaturization have led to the design of portable devices with extremely high performance that can be taken out and used for field-based investigations. Therefore, this study focuses on the use of handheld Raman spectroscopy for the characterization and identification of samples encountered in various application areas related to forensic science.
The Role of Law EnforcementLaw enforcement agencies responsible for reducing the level of serious crime are being faced with more challenges than ever before. For example, new designer drugs are appearing on street corners around the world almost every day. Additionally, terrorism attacks using various explosive devices are being reported by the media around the globe on a regular basis. Also, a topic of international importance is the increase in production of counterfeit cancer, malaria, prescription, and over-the-counter (OTC) drugs, particularly in parts of the world that do not have the skill and expertise to detect them (9). As a result, there is clearly a need to investigate these events in a speedy and timely manner.
This fact is supported by investigations into the illegal use of both social and performance-enhancing drugs, where an identification needs to be made on the type and source of the material used as quickly as possible. Traditionally, test kits are used to obtain a positive indication of a particular drug for presumptive evidence purposes. Unfortunately, for some of the newer, more exotic, and designer drugs of abuse, specific test kits may not be available. Since limited testing can be carried out in the field, seized samples are subsequently sent to a state or federal laboratory for confirmatory analysis. Overburdened laboratories may require weeks or even months before test results reach the prosecutor's hands and, as a result, the pressure placed on analytical chemists to process samples as quickly as possible can be quite significant.
Forensic laboratories that provide evidence for the positive identification of these kinds of samples frequently use gas chromatography–mass spectrometry (GC–MS), which is considered the gold standard for the analysis of volatile organic compounds. However, even though GC–MS provides definitive results, it is a costly, destructive, laboratory-based technique that is extremely time-consuming and contributes to the backlog of samples, subsequently delaying the reporting of results back to law enforcement agencies waiting to prosecute cases.
For that reason, state-of-the-art analytical techniques being used for rapid screening and confirmatory identification are now being miniaturized and making their way into field instrumentation. The transition from laboratory-based to field-based analyzers allows law enforcement agencies to conduct reliable measurements at the point of use, lessening the burden on crime laboratories, reducing their sample backlog, and accelerating the prosecution process. One of the most exciting analytical techniques that is moving analysis away from the laboratory and into the field is portable Raman spectroscopy. Before we take a look at how this new technique is revolutionizing the forensic analysis landscape, let's take a brief look at its fundamental principles of operation.