Organic Thin-Film Transistors as Cannabinoid Sensors: Effect of Analytes on Phthalocyanine Film Crystallization

With a growing international trend of Cannabis legalization, there is a present need for on-the-spot, low cost, and rapid detection of cannabinoids. Here, relationships between thin-films of phthalocyanines (Pcs) with a variety of central, peripheral, and axial substituents and their response to the cannabinoid Delta(9)-tetrahydrocannabinol (THC), with and without a cannabinoid-sensitive chromophore (Fast Blue BB) are investigated through organic thin-film transistor (OTFT) performance. X-ray diffraction and UV-vis absorption spectroscopy measurements demonstrate significantly altered film morphologies and the formation of new crystal orientations in response to analytes, which are corroborated by scanning electron microscopy. Electron paramagnetic resonance further corroborates shifting crystal structures in response to THC and also reveals the formation and promotion of Pc radical species through THC-metal coordination. With exposure to THC, aluminum chloride Pc generates the largest physical film changes as well as the largest changes in OTFT performance. These findings suggest that the semiconductor thin-film morphologies in Pc-based OTFT sensors are not static in the presence of analytes and that the sensing response is driven both by strong analyte-Pc coordination and bulk film restructuring to accommodate these interactions.