Surface plasmon resonance (SPR) spectroscopy is a biosensor technology, that uses the detection of changes in mass in an evanescent wave field (Figure 4). Biomolecules like proteins, peptides and nucleic acids are immobilized on the surface of a sensor chip and possible binding partners are flushed over the surface. Interactions with the immobilized binding partner are detected by a change in refractive index close to the chip surface. Time-courses of these changes are monitored and displayed as sensorgrams and allow the determination of kinetic parameters. Current projects are:

• Molecular mechanisms in myristoyl-switch sensor proteins

• Immobilization of phospholipid layers on sensor chips to study membrane proteins

• Investigation of G-protein coupled receptors and protein complexes on surface-modified sensorchips

Principle of surface plasmon resonance

Figure 4: Principle of surface plasmon resonance. A light source emits monochromatic light that traverses through a prism at a certain angle θ and that is totally internally reflected at an interface of two media. A thin metal layer is at the boundary between the prism and a medium of lower refractive index (e.g. aqueous buffer). Interaction of the evanescent electric field and the electron constellations of the metal causes a reduction in the reflected light intensity (RI). This is illustrated as a gray shadow in the reflected light beam and as a decrease of RI in the graph RI versus θ . Changes of the dielectric properties in the vicinity of the metal surface changes the resonance conditions and leads to a shift of θ (I --> II).