Discovery of a Simultaneous False Positive and Negative Illicit Drug Identification with Portable Surface Enhanced Raman Spectroscopy (SERS)

For many decades, the standard procedure for testing suspected controlled substances in the field involved the use of color-based presumptive tests. Although color tests are sensitive with low limits of detection, they have several recorded limitations, including a lack of specificity. A majority of instrumental methods used in the forensic analysis of illicit drugs in the laboratory have portable field versions. However, portable spectrometers may have meaningful differences in their performance characteristics when compared to their benchtop counterparts, which must be evaluated and understood prior to use of these instruments in the forensic field. When using surface enhanced Raman spectroscopy (SERS), a technique that enhances Raman Scattering there can be meaningful improvement in the limits of detection for illicit drugs to include trace-level detection for analytes of interest.

When evaluating the TruNarc™ Handheld Narcotics Analyzer (a Raman spectrometer with a 785-nm laser) for the detection and identification of low dose fentanyl mixtures, a false positive for cocaine and false negative for fentanyl (0.1%) in acetaminophen was identified using the Thermo SERS H kit. This SERS kit has a gold nanoparticle infused substrate in a polycarbonate holder, and a solvent for dissolving a sample. Interestingly, this fentanyl false negative has a library positive result for cocaine, meaning it is also a false positive for cocaine. This false positive for cocaine and false negative for fentanyl will complicate subsequent laboratory testing, has safety implications, and may have legal ramifications.

References:
1. SWGDRUG. 2022. Scientific Working Group for the Analysis of Seized Drugs (SWGDRUG) Recommendations. Version 8.1, United States Department of Justice
2. ASTM International. 2017. Standard Practice for Identification of Seized Drugs. ASTM E2329-17