Plasmonic biosensors relying on biomolecular conformational changes: Case of odorant binding proteins

Plasmonic nanostructures serve in a range of analytical techniques that were developed for the analysis of chemical and biological species. Among others, they have been pursued for the investigation of odorant binding proteins (OBP) and their interaction with odorant molecules. These compounds are low molecular weight agents, which makes their direct detection with conventional surface plasmon resonance (SPR) challenging. Therefore, other plasmonic sensor modalities need to be implemented for the detection and interaction analysis of OBPs. This chapter provides a guide for carrying out such experiments based on two techniques that take advantage of conformation changes of OBPs occurring upon specific interaction with their affinity partners. First, there is discussed SPR monitoring of conformation changes of biomolecules that are not accompanied by a strong increase in the surface mass density but rather with its re-distribution perpendicular to the surface. Second, the implementation of surface plasmon-enhanced fluorescence energy transfer is presented for the sensitive monitoring of conformational changes of biomolecules tagged with a fluorophore at its defined part. Examples from our and other laboratories illustrate the performance of these concepts and their applicability for the detection of low molecular weight odorant molecules by the use of OBPs attached to the sensor surface is discussed.