There is a key need for better testing for tetrahydrocannibanol (THC), the principal psychoactive ingredient in cannabis. Existing testing methods such as urine testing can often show positives weeks after cannabis consumption, so as more states and countries around the world begin to legalize marijuana for recreational use, the ability to perform roadside or job-site testing that accurately reflects potential impairment levels from THC is critical. In this paper a lateral flow immunoassay (LFA) is performed by looking at the light absorption thermal profile of gold nanoparticles. Using an infrared camera, and a standard paper-based LFA for THC results using lock-in thermography (LIT) imaging were compared to a controlled study of visual analysis of the same LFAs. The visual analysis method was able to reliably observe down to 10 ng/ml, while the LIC was able to record to 2 ng/ml which is significantly better than any field tests currently in use. Future work will look at replacing the laser source with low-cost green LEDs to reduce the setup cost from US$7k to US$250, and the authors see strong potential for use of this analysis technique in other applications such as food pathogen or disease biomarker detection.

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