The evolutionary conservation of the sense of smell tells how important and well-functioning it is. Olfactory proteins (odorant binding proteins, OBPs) are capturing selectively a set of small molecules and therefore deciding which ones are sensed to be odorous and which ones not. Inspired by these proteins, the latest generation of biosensors relies on the binding capabilities of odorant binding proteins, communicatively linked to an electronic transducer. Along these lines a reduced graphene oxide field effect transistor is presented in this thesis, functionalized by an odorant binding protein, for the real-time detection of unlabeled small molecules - like odorants - in a concentration dependent manner. The results demonstrate the suitability of AmelOBP14 - the odorant binding protein from the honey bee Apis mellifera - for biosensors, when immobilized, it is able to bind and discriminate selectively ligands. Furthermore the recombinant odorant binding proteins can be engineered adapting the affinity range of the sensor. The biosensor is demonstrated for the screening of potential interaction partners of odorant binding proteins from the beetle Tribolium castaneum. The OBPs TcasOBP9A and B were identified as capture molecules for agriculture pest markers 6-Methyl-5-hepten-2-one (Sulcatone) and (S)-(+)-3-Octanol. Deciphering the odorant's capability i) to interact with proteins and ii) to activate the insect's olfactory response of the antenna was investigated with two biosensors, in-vitro and in-vivo. The in-vitro method is an OBP-functionalized reduced graphene oxide - field effect transistor (rGO-FET) based sensor which monitors the odorant interaction with the odorant binding protein. A second, orthogonal method was capable to identify the odorantś capability to activate the insect's olfactory response of the antenna in-vivo. Beside the detection of weak binding small ligands for odorant binding proteins, applications for medical diagnostics like the detection of the interaction of antibodies, food derived toxins and aptamer based hormone detection is shown with the biosensor. This thesis introduces the bioelectro-interfacial nano-sensor for real-time and high-throughput, quantitative analysis of protein-ligand interactions based on reduced graphene oxide - field effect transistor sensing.