Surface Plasmon Resonance
Eric Sundberg, Ph.D., Scientist
The interaction of biomolecules with one another is essential for all cellular processes. Surface plasmon resonance (SPR) technology allows us to answer many basic questions about these biomolecular interactions, including: How specific is the interaction? How fast is the interaction? How strong is the interaction?
SPR arises when light is reflected under certain conditions from a conducting film (such as a thin layer of gold) at the interface between two media of different refractive index (such as a surface onto which one biomolecular binding partner is immobilized and the sample, which contains the second biomolecular binding partner in solution). SPR causes a reduction in the intensity of light reflected at a specific angle. This angle varies with the refractive index close to the surface of immobilized molecules.
If the biomolecular binding partner in solution binds to the biomolecule immobilized on the sensor surface, the concentration, and thus the refractive index, changes and an SPR response is measured. Plotting the SPR response versus time during the course of the interaction provides a quantitative measure of the association rate of the binding event. Once the biomolecules reach a binding equilibrium on the sensor surface, the introduction of buffer, in which no soluble biomolecule is present, will cause the displacement of the soluble binding partner and again result in a change of the refractive index and a measurable SPR response. Plotting this response versus time provides a measure of the dissociation rate. Together, the association and dissociation rates of a molecular interaction describe the kinetics (or speed) of the binding event, and their quotient is a direct measure of the affinity (or strength) of the interaction.
Our instrument for SPR analysis of biomolecular interactions is the Biacore 3000. This instrument is the highest performance research system available for such analysis, providing non-invasive, label-free and real-time measurements of binding events. The sensitivity range of the instrument allows for the analysis of interactions involving small molecules, proteins, nucleic acids, viruses, lipid vesicles, crude extracts and whole cells. A computer-driven microfluidic system allows for completely automated interaction analysis. A specialized sample recovery unit provides the option of recovering only the bound molecules from a mixed sample population in a state that is suitable for further analysis, such as by mass spectrometry.