By Dawn Yang, Kristen Frano, John Maticchio
B&W Tek
Introduction
In recent years, handheld Raman devices have become a widely used technology for safety and security personnel and law enforcement for quick identification of narcotics, pharmaceutical drugs, hazardous chemicals, explosives, and other substances. Thanks to the rugged design and portability of handheld Raman devices, police officers and public safety personnel are able to detect suspected substances in the field.
However, brightly-colored street samples such as ecstasy tablets pose a serious challenge due to the fluorescence interference commonly associated with Raman devices that use a 785-nm laser. Fluorescence is photoluminescence emission upon laser excitation that potentially overwhelms the Raman signal partially or completely, resulting in a poorly defined Raman signature, and failure of identification. Fluorescence can limit the Raman detection of colorful substances and mixtures with plant-based narcotics and cutting agents, making it difficult to perform fast, presumptive tests of street samples in the field.
Case Study: Ecstasy
Popular among teenagers and young adults, ecstasy tablets are often found in many colors with various logos at club scenes and rave music events to attract young people. The main ingredient MDMA (3,4-methylenedioxymethamphetamine) is a synthetic drug, chemically similar to those of stimulants and hallucinogens that alters mood and perceptions. Listed by the US Drug Enforcement Administration (DEA) as Schedule I drug, MDMA has high potential for abuse. Deaths from MDMA are commonly associated with a fatal increase in body temperature and dehydration.
Due to the colorful and nonhomogeneous nature of ecstasy pills, when they are measured with a Raman device with a 785-nm excitation wavelength the Raman signatures tend to be overwhelmed by strong fluorescence, which limits the capability of identification. To illustrate the fluorescence interference of colorful ecstasy pills generated by a 785-nm laser, Figure 1 shows Raman spectra collected from a pink-colored MDMA tablet using a Raman device with a 785-nm laser (blue trace) and a Raman device with a 1064-nm laser (red trace). The fluorescence generated from the 785-nm laser overwhelms the Raman peaks characteristic of MDMA, while excitation with the 1064-nm laser results in clear, distinct MDMA Raman signature peaks