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Marijuana or cannabis is becoming lawful in North America and many countries of the world. About 23 states and the District of Columbia in the United States have recently legalized the medical use of cannabis. Four states (Alaska, Colorado, Oregon, and Washington) have even legalized its recreational use. Tetrahydrocannabinol (THC) is one of the most psychoactive agents in cannabis that causes intoxication during driving. It is needed to develop portable tools for enhanced detection of THC influenced drivers in order to keep our roads safe.
To date several detection techniques have been reported to identify THC from blood, urine, hair, sweat, and saliva. But, most of those anylysis are laboratory dependent. The use of bulky equipments such as chromatography and mass spectroscopy for analyzing THC in blood sample make it incompatible for road tests. Moreover, the most widely used urine tests cannot detect THC immediately after intake of cannabis. Recently, Stanford researchers developed mobile “potalyzer” based on magnetic biosensors to detect tiny THC molecules in human saliva. Besides, police officers could collect oral fluids with a cotton swab and test the saliva using magnetoresistive biosensors and read the results on an integrated smartphone. However, it is thought that the origin of THC in saliva is oral mucosal depots instead of blood. Then, the consumption of cannabis through edibles will make difficult to detect THC in saliva.
Currently, there has no portable device in the market to provide quick and precise identification of a driver’s THC intoxication as effectively as breathalyzer for alcohol intoxication. Here, we proposed a field effect transistor based biosensor technology that facilitates rapid and precise measurement of THC intoxication from driver’s breath.
The detection technique is based on change of conductivity in MoS2 nanosheets due to interaction between THC molecules and MoS2 through anti-THC antibody and gold nanoparticles (AuNPs).
Proposed biosensor for detecting THC:
To fabricate the MoS2 EFT biosensor, the chemically exfoliated few-layer MoS2 dispersion will be deposited on a 200 nm Si/SiO2 substrate. 80 nm Au will be deposited as source and drain electrodes. Au NPs of 10 nm will be deposited onto the surface of the MoS2 film using a DC sputtering. Then, 5 μL of 5 μg/mL anti-THC antibody solution will be injected onto the active area of the device, and incubated for 15 mins at room temperature. Finally, the device will be rinsed with DI water to remove the unbound antibodies and dried with N2 blow.
AuNPs are used to bind anti-THC antibody on MoS2 surface. The anti-THC antibody acts as anchor sites for THC molecules. Electrons transfer from negatively charged oxygen in THC to AuNPs and then AuNPs to MoS2, resulting in an increased electron concentration in the MoS2 nanosheets. Thus, the electrical conductivity in the n-type MoS2 channel will increase with exposure to THC. The strong affinity of anti-THC antibody towards THC will make the biosensor more selective. Although there is no clear scientific limit on THC for drivers intoxication, most previous reports suggests the values ranging from 2 to 25 ng/mL. The concentration of anti-THC antibody, incubation time, and diameter of AuNPs will be optimized in order to achieve better sensitivity in this range. The anti-THC antibodies bind the THC on AuNPs, leading to the change in the electrical conductivity of MoS2 as a sensor signal.
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