Functionalized graphene sensors for detecting coffee-related compounds

Coffee is a globally consumed beverage that needs high quality and production standards. Consequently, concerns regarding its quality are widespread, making the identification of its chemical components and of potential substances resulting from the cultivation process highly desirable. In this work, theoretical calculations based on the density functional theory combined with non-equilibrium Green’s function were employed to assess the potential of graphene-based devices for molecular detection and sensing. The quantum calculations were used to investigate the interaction between graphene-based systems (including pristine graphene and oxygen-containing graphene sheets) and individual molecules such as caffeine, trigonelline, and glyphosate. The binding energy analysis revealed that epoxy- and hydroxyl-functionalized graphene sheets exhibit a stronger interaction with the target molecules in comparison with pristine graphene. The transmission curve obtained for each molecule allowed the identification of individual molecules on the devices based on conductance changes. Since reduced graphene oxide (rGO) is known to contain a distribution of oxygen functional groups (such as epoxy and hydroxyl groups) surrounded by large regions of interconnected hexagonal rings of sp${}^2$${}^2$-hybridized carbon atoms, the obtained results indicate then that different types of target molecules can be detected using an rGO-based device. This underscores the capability of carbon-based materials to exhibit remarkable sensitivity and selectivity in the detection of organic molecules, which are of special interest for molecular sensing applications in general and for the coffee production sector in particular.