Pioneer SPR Principles
Surface plasmon resonance (SPR) technology can be used to probe for affinity and kinetics between a range of molecules from small-molecule fragments to virus particles without the need for labels for detection. Binding interactions are monitored in a biosensor that is comprised of a thin gold-coated glass slide.
In most cases, a dextran matrix is attached to the gold coating, which acts as a substrate to which specific immobilization chemistries can be introduced to attach one binding partner to the biosensor. The other binding partner will be introduced to the biosensor using an automated fluidic system.
When light is made to pass through the biosensor surface and is reflected off the gold coating, at a certain angle of incidence, a portion of the light energy couples through the gold coating and creates a surface plasmon wave at the sample and the gold surface interface.
The angle of incident light required to sustain the surface plasmon wave is sensitive to refractive index changes that is proportional to mass changes at the surface (Figure 1).
A typical SPR binding assay is shown in Figure 2. As mass accumulates at the sensor surface during a binding interaction, the refractive index increases, and an increase in response signal is observed.
After the sample is replaced by buffer, mass will decrease at the surface due to dissociating molecules and reduce the resonance unit response. By repeating this cycle at different concentrations, calculations can be made for ka (on-rate) and kd (off-rate) and binding affinity of the biomolecular interaction (Figure 2).