Abstract
With recent changes in the legalization of cannabis around the world, there is an urgent need for rapid, yet sensitive, screening devices for testing drivers and employees under the influence of cannabis at the roadside and at the workplace, respectively. Oral fluid lateral flow immunoassays (LFAs) have recently been explored for such applications. While LFAs offer on-site, low-cost and rapid detection of tetrahydrocannabinol (THC), their nominal detection threshold is about 25 ng/ml, which is well above the 1-5 ng/ml per se limits set by regulations. In this paper, we report on the development of a thermo-photonic imaging system that utilizes the commercially available low-cost LFAs but offers detection of THC at unprecedented low concentrations. Our reader technology examines photothermal responses of gold nanoparticles (GNPs) in LFA through lock-in thermography (LIT). Our results (n = 300) suggest that the demodulation of localized surface plasmon resonance responses of GNPs captured by infrared cameras allows for detection of THC concentrations as low as 2 ng/ml with 96% accuracy. Quantification of THC concentration is also achievable with our technology through calibration.
Highlights
Cannabis and its byproducts are the most widely used psychoactive substances worldwide [1]
lateral flow immunoassays (LFAs) strips for THC saliva test were spiked at various concentrations of THC and inspected visually by adults and a lock-in thermography (LIT) imaging system
At high THC concentrations (e.g., 25 ng/ml), THC binds effectively with the antibodies present in the LFA sample pad; the antigen immobilized at the test line is unable to restrain with antibody conjugate, preventing the gold nanoparticles (GNPs) from being fixed on the test line and yielding lack of signal at the test line
Summary
Cannabis and its byproducts are the most widely used psychoactive substances worldwide [1]. Accurate measurement of THC in blood has proven to be challenging as withdrawal of blood samples need to take place in medical facilities, causing a significant delay in sampling (usually 1-2 hours) during which THC concentration in the blood dramatically drops [14]. To overcome this systematic source of error in screening, and allow for proper enforcement of regulations, law enforcement in most jurisdictions have advocated and, even regulated, the use of devices that screen and measure THC in accessible bodily fluids such as oral fluid [15]. Studies suggest a close correlation between the concentration of THC in blood and oral fluid, especially about half an hour after consumption [16]
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