Engineering Cannabinoid Sensors through Solution-Based Screening of Phthalocyanines

Abstract

Organic thin-film transistors (OTFTs) have shown promise for a range of sensing applications, with phthalocyanine-based OTFTs demonstrated as sensors for atmospheric parameters, volatile gases, and small organic molecules including cannabinoids. However, the process of fabricating, testing, and optimizing OTFTs in a laboratory setting requires highly specialized equipment, materials, and expertise. To determine if sensor development can be expedited and thus reduce manufacturing burden, spectroelectrochemistry is applied to rapidly screen for molecular interactions between metal-free phthalocyanines and a variety of metal phthalocyanines (MPcs) and the cannabinoids Δ9-tetrahydrocannabinol (THC) or cannabidiol (CBD), with and without a cannabinoid-sensitive chromophore (Fast Blue BB). Spectral analyses are corroborated by 2D-NMR and related to measured OTFT performance. Spectroelectrochemical changes to the Q band region of the phthalocyanine spectra in the presence of analytes can be used to predict the response of OTFTs. Thus, with spectroelectrochemistry, a range of potential materials for OTFT small organic molecule-sensing applications can be quickly analyzed, and phthalocyanines with a preferred response can be selected.

Metal phthalocyanines: thin-film formation, microstructure, and physical properties

“…However, solvent coordination and aggregation can result in peak shifts uncharacteristic to the MPc itself. 145 Additionally, solid state UV-vis absorption includes effects of thin-film molecular packing and crystal structures that are not visible in solution. MPcs typically display two strong absorption bands, one in the UV region of 280–350 nm known as the B (Soret) band, and the stronger, often better resolved, band in the visible region between 550–750 nm known as the Q band ( Fig.…”

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

“…With the subsequent addition of THC, the peak maximum of AlClPc red shifts from 686 to 689 nm, suggesting altered analyte‐Pc coordination states similar to those observed in solution in our previous work. [ 13 ] This is further corroborated by the SEM images (Figure 3), suggesting the unique crystal structure of AlClPc is particularly susceptible to analyte‐induced physical film effects. These results provide evidence that metal and substituent differences in the Pcs alter Pc‐analyte interactions, resulting in the observed variations of analyte induced crystals.…”

“…[ 46,56 ] Upon exposure to both FBBB(B) and THC, CuPc also has an increase in its second Q band (695 nm), albeit much lower in relative intensity to that of CoPc, further suggesting the absorbance peak intensity shifts are a result of strong FBBB(B) + THC conjugate interactions. In our previous work, [ 13 ] H 2 Pc was found to uniquely coordinate with the FBBB(B) + THC conjugate in solution. The absorbance spectra of the H 2 Pc thin‐film shows the appearance of two additional broad peaks, centered at 499 and 583 nm, when exposed to FBBB(B) + THC, another indication of η‐crystal formation.…”

“…In our previous work, following exposure to FBBB(B), subsequent additions of THC to the surface of OTFTs, at concentrations as low as 200 n m , was found to produce strong effects on device performance, and demonstrated as ratiometric sensors, [ 24 ] as well as spectroelectrochemical responses for a variety of soluble Pcs. [ 13 ] We previously established that the combination of FBBB(B) and THC was necessary to produce large decreases in μ in CuPc and F 16 ‐CuPc. [ 24 ]…”

“…[ 4,5 ] Pc‐based OTFTs have been demonstrated in a variety of liquid [ 6–9 ] and gas [ 10–12 ] sensing applications, including the ratiometric detection and differentiation of Δ 9 ‐tetrahydrocannabinol (THC, Figure iii) and cannabidiol (CBD) recently described by our group. [ 13,14 ] The plant Cannabis sativa is cultivated for multiple purposes, including its fibers and seed/oil (hemp), but is primarily used for therapeutic and recreational purposes attributed to the pharmacological effects of the unique cannabinoids concentrated within the inflorescence. Among over 100 identified cannabinoids, tetrahydrocannabinolic acid (THCa) and cannabidiolic acid (CBDa) are typically the most abundant, with their respective decarboxylated forms, THC and CBD, the most studied and recognized for their psychoactive and therapeutic potential.…”