Team:Queens Canada/Description

We aim to use recombinantly expressed antibody fragments, which are conjugated to fluorescent molecules, to detect tetrahydrocannabinol (THC) – the active ingredient in marijuana. This novel immuno-assay would allow for a specific detection method with minimal cross-reactivity.

Why Develop a THC Immunoassay?

Tetrahydrocannabinol (THC) is the major psychoactive ingredient in marijuana; yet, there is currently no cheap, specific, and sensitive assay for its detection. In Canada, devices for roadside THC testing have been approved, however there is concern about their specificity. For example, the Draeger Drug Test 5000 has been shown to have a false positive 14.5% of the time (1). We believe the issue of specificity could be addressed by a handheld fluorescent immunoassay. Therefore, we aim to establish an assay using genetically engineered recombinant antibody fragments.

Development of a Handheld Immunoassay

For detection of the fluorescently labelled antibody, we aim to use lipophilic membranes and a photon counter. THC is a highly lipophilic molecule; therefore, it could be absorbed by a lipophilic membrane, such as oil only sorbent pads, or polyvinylidene difluoride (PVDF). In principle, the lipophilic membrane will absorb THC, which the fluorescently labelled antibody can then bind to (Fig. 1A). Due to the lipophobic (hydrophilic) nature of antibodies, the antibodies are not expected to stick to the membrane in the absence of THC (Fig. 1B).

The hydrophobic membranes, alongside an antibody solution, can be implemented into a portable photon counter (Fig. 2). The membrane can be housed in a removable compartment, which allows for switching the membrane after each test. An LED can be used to excite the antibody inside the device, and the emission can be determined via a photon counter. The antibodies will be housed in a replaceable cartridge. A handheld prototype will be made to automate the detection process and will serve as a proof of concept.

Figure 1. Explanation of the theory behind the novel immunoassay for THC detection. Note that this concept could be adapted to other lipophilic antigens.

Figure 2. Computer assisted design (CAD) illustration of the THC roadside test sensor. The openings at the top correspond to the wash (left) and antibody (right) chamber, respectively. The pinch-drawer on the side of the device house the replaceable lipophilic membrane. A photon counter, Arduino board, and OLED display will be used to measure and display the fluorescent signal.

Sources

1. Gjerde, H., Clausen, G. B., Andreassen, E., and Furuhaugen, H. (2018) Evaluation of Dräger DrugTest 5000 in a Naturalistic Setting. J Anal Toxicol. 42, 248–254