Graphene field-effect transistor sensor for detection of urea in water: Experimental study and DFT analysis

Urea sensors are used in medicine for disease monitoring, the automotive industry for emission control, agriculture and food safety for fertilizer and residue analysis, environmental monitoring for water pollution detection, and in industrial processes for production control. This article presents a pioneering experimental study of non-selective urea detection in aqueous solution using graphene doping in a field-effect transistor (FET) configuration. It is demonstrated that water itself p-dopes graphene, while the addition of urea weakens this effect (resulting in reduced p-doping). The response is explained by original density functional theory (DFT) calculations considering the common influence of water and urea. Analyses of charge redistributions and band structures indicate the formation of non-doping urea–water complexes responsible for the observed results. Moreover, the calculations provide deeper insight into the complex urea–water–graphene interactions, which may be utilized in other applications.