An electrochemical aptasensor for A9-tetrahydrocannabinol detection in saliva on a microfluidic platform

We present a novel on-off, cost-effective, rapid electrochemical aptasensor combined with a microfluidics cartridge system for the detection of Delta(9)-THC (Delta(9)-tetrahydrocannabinol) in human saliva via differential pulse voltammetry. The assay relied on the competitive binding between the A9-THC and a soluble redox indicator methylene blue, using an aptamer selected via FRELEX. We found that the aptasensor can detected 1 nM of Delta(9)- THC in PBS in a three-electrode cell system, while the sensitivity and both the dissociation constant (K-d) and association constant (K-b) were dependent on the aptamer density. The aptamer also showed great affinity to-wards Delta(9)-THC when tested against cannabinol and cannabidiol. The same limit of detection of 1 nM in PBS was achieved in small volume samples (similar to 60 mu L) using the aptamer-modified gold screen-printed electrodes combined with the microfluidic cartridge setup, however, the presence of 10% raw human saliva had a negative effect which manifested in a 10-fold increase in the LOD due to interfering elements. Filtering the saliva, improved the tested volume to 50% and the LOD to 5 nM of Delta(9)-THC which is lower than the concentrations associated with impairment (6.5-32 nM). The aptasensor showed a good storage capability up to 3 days, however, the reusability significantly dropped from 10 cycles (freshly prepared) to 5 cycles. The results clearly demonstrate the feasibility of the aptasensor platform with the microfluidics chamber towards a point-of-care testing application for the detection of Delta(9)-THC in saliva.

Automated summary

We have developed a new on-off, cost-effective, and rapid electrochemical aptasensor combined with a microfluidics cartridge system for the detection of Delta(9)-THC in human saliva. The sensor showed a high sensitivity to Delta(9)-THC and can detect it at a concentration as low as 1 nM in PBS. However, the presence of raw human saliva significantly increased the limit of detection due to interfering elements. With saliva filtration, the limit of detection improved to 5 nM, which is lower than the concentrations associated with impairment.