Researchers at Oregon State University examine a more efficient method for the detection of THC in body fluids.

Credit for featured photo: Michal Jarmoluk from pixabay

Marijuana is one of the most commonly used psychoactive drugs in the country. Marijuana contains the well-known compound THC (D9-tetrahydrocannabinol), which is responsible for many of its effects, such as increased heart rate and reddening of the eyes. When THC enters the body, the compound can end up in various body fluids such as saliva, urine, and blood. This fact allows toxicologist to detect THC for a variety of forensic applications. Among these applications are preventing drug abuse and determining if someone is driving under the influence.

Figure 1: Instruments, such as the one above, are typically used to analyze drugs. Above is a gas chromatography machine, which can be used to confirm the identity of drugs. Credit: creative commons

Current methods for the detection of THC and other illicit drugs require extensive sample preparation and long data processing times. This can waste precious time in a forensics investigation. Surface Enhanced Raman Spectroscopy (SERS) has potential for being a quicker but accurate alternative. In Raman spectroscopy, light is used to irradiate a sample, however, the energy that passes through the sample (or rather, is scattered by it) is different than the energy used to irradiate it. A spectrum can be created from this shift in energy, or “Raman” shift, and the unique chemical information can then be used to identify a compound. SERS uses a substrate (often a precious metal like gold or silver) to make the signal for the Raman spectrum stronger, making it possible to analyze miniscule amounts of sample.

Figure 2: In SERS, a sample is deposited on silver or gold nanoparticles, which enhances the Raman signal.

While SERS has been used to detect THC in a methanol solution (since it serves as a standard that can be used to calibrate the system and prepare it for more complex analysis), work has yet to be done on using SERS to detect THC in body fluids. For this reason, the Micro- & Nano-photonics Research Group at Oregon State University sought to determine if SERS could be used to detect THC in blood plasma and saliva.

THC was added at various concentrations to methanol (the positive control), blood plasma, and purified saliva. The solutions were loaded onto the SERS substrate, and the Raman spectra of the samples were collected using a Raman microscope. Using advanced statistical methods like principal component analysis, Sivashanmugan et al. showed that their method could be used to detect THC at various concentrations, as low as 10­-12 M, in the selected body fluids. That is 1 mol of THC for every 1 trillion liters of solution. Such a low detection limit is especially important in forensic science, since small traces of body fluids are often retrieved from crime scenes for analysis.

In addition to looking at THC in various body fluids, Sivashanmugan et al. monitored the degradation of THC in body fluids over time. When THC is present in body fluids, it undergoes a process known as metabolization, where it turns into less active compounds that can be eliminated from the body with greater ease. One of the metabolites of THC is THC-COOH, which has a carboxylic functional group attached to the main ring. Since metabolites like THC-COOH are present in body fluids after marijuana use, rather than THC itself, toxicologist test for the presence of these metabolites in body fluids. In order to look at the degradation, or metabolization, of THC in body fluids over time, Sivashanmugan et al. used SERS to collect the Raman spectra of THC in raw saliva over the course of 9 hours. Using advanced statistical methods, they were able to characterize the metabolization of THC into metabolites such as THC-COOH in raw saliva.

The method developed by Sivashanmugan et al. detects THC in various body fluids as well as characterizes the metabolization of THC into THC-COOH. This technique has potential to be applied as a sensing technique for the detection of marijuana abuse. Due to the shorter sample preparation and data analysis time associated with SERS, implementing this method could save forensic toxicologist valuable time.

Title Trace Detection of Tetrahydrocannabinol in Body Fluid via Surface-Enhanced Raman Scattering and Principal Component Analysis
Authors Kundan Sivashanmugan, Kenneth Squire, Ailing Tan, Yong Zhao, Joseph Abraham Kraai, Gregory L. Rorrer, Alan X. Wang
Journal ACS Sensors
Year March 2019
Link https://pubs.acs.org/doi/10.1021/acssensors.9b00476
Citation Sivashanmugan, K.; Squire, S.; Tan, A.; Zhao, Y.; Kraai, J. A.; Rorrer, G. L., Wang, A. X. Trace Detection of Tetrahydrocannabinol in Body Fluid via Surface-Enhanced Raman Scattering and Principal Component Analysis. ACS Sens. 2019, 4, 1109-1117.

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