Abstract
Marijuana is listed as a Schedule I substance under the American Controlled Substances Act of 1970. As more U.S. states and countries beyond the U.S. seek legalization, demands grow for identifying individuals driving under the influence (DUI) of marijuana. Currently no roadside DUI test exists for determining marijuana impairment, thus the merit lies in detecting the primary and the most sought psychoactive compound tetrahydrocannabinol (THC) in marijuana. Salivary THC levels are correlated to blood THC levels making it a non-invasive medium for rapid THC testing. Affinity biosensing is leveraged for THC biomarker detection through the chemical reaction between target THC and THC specific antibody to a measure signal output related to the concentration of the targeted biomarker. Here, we propose a novel, rapid, electrochemical biosensor for the detection of THC in saliva as a marijuana roadside DUI test with a lower detection limit of 100 pg/ml and a dynamic range of 100 pg/ml – 100 ng/ml in human saliva. The developed biosensor is the first of its kind to utilize affinity-based detection through impedimetric measurements with a rapid detection time of less than a minute. Fourier transform infrared spectroscopy analysis confirmed the successful immobilization of the THC immobilization assay on the biosensing platform. Zeta potential studies provided information regarding the stability and the electrochemical behavior of THC immunoassay in varying salivary pH buffers. We have demonstrated stable, dose dependent biosensing in varying salivary pH’s. A binary classification system demonstrating a high general performance (AUC = 0.95) was employed to predict the presence of THC in human saliva. The biosensor on integration with low-power electronics and a portable saliva swab serves as a roadside DUI hand-held platform for rapid identification of THC in saliva samples obtained from human subjects.
Highlights
Regular use of marijuana shows an increased risk of addiction and the use of other illicit drugs[5]
Gold thin films were deposited on PET substrates using e-beam vapor deposition at parameters mimicking those used for sensor fabrication and used for fourier-transform infrared spectroscopy (FTIR) analysis
Prior to FTIR measurements, each sample was rinsed thoroughly with DI water dried with N2 air to rid the surface of any unbound material that may interfere with the analysis
Summary
Regular use of marijuana shows an increased risk of addiction and the use of other illicit drugs[5]. THC can be detected in blood for up to 5 hours with a cutoff limit of 10 ng/mL, in urine for up to 95 days with a cutoff limit of 15 ng/mL, and in saliva for up to 34 hours with a 0.5 ng/mL limit[13,14] These values are based on only a few seminal studies as approval for testing illicit products like marijuana are difficult to get approval for. Despite that salivary THC levels have only an insignificant contribution directly from THC in blood, the time course in these two biological fluids follow very similar concentration profiles[16] This finding suggests that saliva is a good indicator for active drug use
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