Can metal nanoparticles and portable lasers detect synthetic cannabinoids in saliva?

Credit for featured photo: Domonic Milton Trott from Flicker available via Creative Commons (CC).

While overdosing on traditional marijuana is unlikely, the consumption of another emerging class of cannabinoids poses a risk to public health; synthetic cannabinoids (SC). These substances are similar in their chemical structure to compounds like THC (Δ-9-tetrahydrocannabinol), however they differ in the identity or connectivity of a few atoms. These slight changes may greatly increase its potency compared to the parent drug. Their novel nature along with our lack of knowledge on their toxicological effects make SCs dangerous. Especially since these substances have already been linked to numerous emergency room visits and even fatalities.

We need a simple test to recognize SCs, known as a screening test, that doctors can use in an emergency room. Such a test could identify those suffering from potent SCs so they can receive the proper treatment, or inform the community which SCs cause adverse effects. Unfortunately, current screening tests, like enzyme-linked immunosorbent assay (ELISA), do not rise to the challenge.

ELISA methods typically immobilize antigens (your molecule of interest, like an SC) to a 96-well plate like the one in Figure 1. Then, antibodies that specifically bind to the antigen are added. After washing away any stray molecules, only the antigen and the attached antibody will remain. The attached antigen-antibody complex is recognized by adding an enzyme that will color the complex, like the blue seen in Figure 1. Thus, wells that change color contain your molecule of interest, like an SC. While ELISAs are useful for the analysis of better-known drugs, they may not effectively distinguish between different SCs. This is because the extent of modification to the molecular structure is subtle enough to fool the ELISA test and may still result in false negatives for SCs.

Figure 1: This figure shows an example of a 96-well ELISA plate. It also shows how a color change is used to determine if a substance is or isn’t present. Source: Ajpolino from WikiCommons available via Creative Commons (CC).

Surface Enhanced Raman Spectroscopy (SERS) recently showed potential as a screening test method as it compensates for these ELISA-based drawbacks. SERS is a form of Raman spectroscopy that uses a metal nanoparticle coated surface (often gold or silver) to enhance the strength of Raman signal, allowing for the detection of trace or miniscule amounts of compounds. SERS is both more sensitive and more selective than ELISA, and does not require any labeling of your molecule of interest, such as the antigen-antibody sandwich.

This potential screening tool is even said to yield a molecular fingerprint based on the molecular structure, not elemental composition. This gives the potential to not only detect SCs, but determine when new ones reach the market. SERS has already been shown to detect other drugs such as benzodiazepines in urine and distinguish between highly similar SC structures. For these reason, the authors of this study choose this technique for a potential screening method. Even more promising, portable Raman spectrometers, like the one in Figure 2, are becoming more widely available and financially accessible to crime labs.

Figure 2: This figure shows an image of a portable Raman Spectrometer. Source: IAEA Imagebank from Flicker available via Creative Commons (CC).

The researchers chose saliva as the main sample in this study for several reasons. Entry level personnel can collect saliva easily compared to blood, which requires a nurse or phlebotomist. Saliva is also difficult to adulterate, or add a substance that interferes with the technical analysis, and can be collected under supervision; unlike urine, where a person gives a sample behind closed doors. Little metabolization or bodily processing occurs in saliva, so the original drug is most likely present for long periods of time, as opposed to its metabolite products, which may not be well known. The study used the SC JWH-018 because it is fairly well-researched.

Figure 3: This figure shows an example of a μ-SPE apparatus, used by the authors in this study to analyze the saliva for SCs. Source: Iarsjuh from Flicker available via Creative Commons (CC).

The researchers from the McCord lab at Florida International University aimed to develop a rapid, qualitative screening method for JWH-018 in saliva without losing sensitivity. To do this, they prepared saliva solutions by adding JWH-018, then removed potentially interfering proteins and salt by adding methanol and performing a micro-solid phase extraction (μ-SPE), the apparatus pictured in Figure 3. Afterwards, the researchers prepared a gold nanoparticle SERS surface and added them to the SC-containing saliva sample before collecting the SERS spectra.

By examining how the intensity of a particular SERS signals varied with the concentration of JWH-018, the McCord group determined the limit of detection or sensitivity of their method. This value describes how little JWH-018 must be present in order to detect it. The limit of detection was found to be 31 nanograms per milliliter, which is equivalent to pouring about 4 tablespoons of salt into an Olympic sized swimming pool. As part of their study, the scientists also collected the SERS spectra of the untampered saliva and found a limit of detection for obtaining any signal of the biological fluid to be around 35.7 nanograms of saliva per milliliter of methanol solution.

These promising results suggest that taking SERS analysis of saliva from someone suspected of taking synthetic cannabinoids can recognize the specific SC they took. Further, the limit of detection of this method is about the same as current screening methods, meaning we lose no sensitivity by switching methods. The most substantial improvement though, was the total time of analysis, which includes sample cleanup and spectral acquisition; SERS took a mere 36 minutes while ELISA methods can take up to 2 hours. This nearly four-fold reduction in analysis acquisition is the largest feather in the hat of the McCord lab’s new method.

If accepted by medical professionals, crime laboratories and the court (which means a Daubert hearing), this method would change how we can rapidly recognize SCs in emergency rooms and improve the treatment of many individuals. Even more promising is that a portable Raman spectrometer achieved sensitivity comparable to current, laboratory-based methods, opening up the ability to perform this test in the field. Both applications of this work are promising, and more research should be done to ensure their use in hospital and emergency clinic settings.

 TitleMicro Solid Phase Extraction Surface-Enhanced Raman Spectroscopy (μ-SPE/SERS) Screening Test for the Detection of the Synthetic Cannabinoid JWH-018 in Oral Fluid
AuthorsChiara Deriu, Irene Conticello, Alexander M. Mebel, and Bruce McCord
JournalAnalytical Chemistry
CitationDeriu, C; Conticello, I.; Mebel, A. M.; McCord B; Micro Solid Phase Extraction Surface-Enhanced RamanSpectroscopy (μ-SPE/SERS) Screening Test for the Detection of theSynthetic Cannabinoid JWH-018 in Oral Fluid. Anal Chem. 2019, 91 (7), 4780-4789. doi: 10.1021/acs.analchem.9b00335.

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