Development of an electrochemical biosensor for ∆9-tetrahydrocannabinol detection based on gold surfaces functionalized with self-assembled monolayers

The cannabis is one of the most widely-consumed drugs in the world. According to the United Nations’ Word drug report, the number of cannabis consumers worldwide was of order of 238 million in 2017 and this number is in constant increase. Certainly, cannabis can be administrated for therapeutic use, and in several medicines; in this case, the administered doses take into account both medical and psychic states of the patients. When consumed as a drug, and depending upon the dose, method of administration and prior experience, cannabis can cause an altered state of consciousness, pulse and heart rate increase, and impaired coordination and concentration. For an equivalent dose of 15 mg of ∆9-tetrahydrocannabinol, the active ingredient of cannabis, the consumer can get attacks of anxiety, hallucinations, delusions and impression of knowing nothing. France has recorded 7 % of fatal accidents involving cannabis’ users drivers. The ∆9-THC, as an example of cannabis, can be detected with its metabolites in the blood, sweat and saliva by chromatographic methods with a limit of detection in the order of 0.4 ng.ml-1. In this context, we have developed a new alternative for ∆9-THC detection: an electrochemical immunosensor. To the very best of our knowledge, this is the first study concerning cannabinoid detection with a biosensor. Here, gold electrodes were first functionalized with a self-assembled monolayer (SAM) of mercaptoundecanoid acid (MUDA), a long-chain carboxylic acid-terminating alkanethiol. The acid groups were then activated with the 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS) before further grafting of anti-cannabinoid monoclonal antibodies. Cyclic voltammetry (CV) and impedance (EIS) electrochemical techniques were used to follow up ∆9-THC antigen detection. All experiments were carried out in phosphate buffer solution (PBS) containing 1 M KCl and 5 mM [Fe(CN)6]-2/-3 redox probe. Electrochemical results showed a wide dynamic range varying between 10-15 and 1 mg.mL-1. The limit of detection of the designed sensor, of order of 10-15 mg/ml, is largely inferior to that obtained with conventional technique techniques. This study paves the way for the development of new analytical devices able to detect cannabis traces in few minutes and in a biological medium.