The Development of a Surface Enhanced Raman Spectroscopy Method for the Detection of Synthetic Cannabinoids in Urine

Abstract

The use and abuse of synthetic cannabinoids has increased significantly in recent years due to their easy access and growing popularity. Despite having more known drugs become illegal, new synthetic versions of these drugs are being made that have not yet been recognized or classified as illegal substances. Therefore, standard methods may not be able to detect these drugs. The most common method of screening detection for drugs of abuse in biological samples is the immunoassay. However, the immunoassay method presents some disadvantages, particularly for newly synthesized compounds. More advanced methods have also been used, such as LC-MS; however, these procedures involve complex sample preparation and long run times. A potential solution to this issue is surface enhanced Raman spectroscopy (SERS). When Raman spectroscopy is performed in the presence of metallic nanoparticles and aggregating agents, the signal can be enhanced several orders of magnitude via the creation hot-spots that results from displacement of the stabilizing agent, which leads to a change in the surface charge of the metallic nanoparticle and the ionic strength of the solution. In the present thesis an optimal SERS method was developed for the detection of synthetic cannabinoids. A variety of aggregating agents and nanoparticles were evaluated using UV/Vis spectrometry, particle sizing and zeta potential for optimal detection of these compounds. Overall, the best analytical procedure used 0.0015 MgCl2 to aggregate spherical gold nanoparticles to detect synthetic cannabinoid parent compounds using a portable Raman spectrometer with a limit of detection as low as 20 ng/mL in pure samples. Then the optimized SERS method was tested on two JWH-018 metabolites producing a limit of detection as low as 37 ng/mL. To determine if the SERS method could be used for practical applications, an additional study was conducted on spiked urine samples using supported liquid extraction (SLE) prior to analysis. Since synthetic cannabinoid parent compounds are not commonly found in urine samples, two JWH-018 metabolites were examined. A few pretreatment methods prior to extraction were examined to determine the optimal SLE method to detect synthetic cannabinoid metabolites. However, the SERS spectrum of the JWH-018 metabolites after the extraction did not match that of the pure drug. Therefore, additional study needs to be conducted to determine other possible extraction methods to detect JWH-018 metabolites using SERS.