Monochromatic light is illuminated vertically on the rear side of a transparent multi-layer substrate. The partial beams of the monochromatic light are transmitted and reflected at each interphase of the multi-layer system. Superimposition of the reflected beams result in destructive or constructive interference (depending on wavelength of the used light and the used substrate/multi-layer system materials) that can be detected in an intensity change of the reflected light using a photodiode, CCD, or CMOS element.
The sensitive layer on top of the multi-layer system can be (bio-)chemically modified with receptor molecules, e.g. antibodies. Binding of specific ligands to the immobilised receptor molecules results in a change refractive index n and physical thickness d of the sensitive layer. The product of n and d results in the optical thickness (n*d) of the sensitive layer.
Monitoring the change of the reflected intensity of the used light over time results in binding curves that provide information on:
* concentration of used ligand
* binding kinetics (association and dissociation rate constants) between receptor and ligand
* binding strength (affinity) between receptor and ligand
* specificity of the interaction between receptor and ligand
Compared to bio-layer interferometry, which monitors the change of the interference pattern of reflected white light, SCORE only monitors the intensity change of the reflected light using a photodiode, CCD, or CMOS element. Thus, it is possible to analyse not only a single interaction but high-density arrays with up to 10,000 interactions per cm.
Compared to surface plasmon resonance (SPR), which penetration depth is limited by the evanescent field, SCORE is limited by the coherence length of the light source, which is typically a few micrometers. This is especially relevant when investigating whole cell assays. Also, SCORE (as well as BLI) is not influenced by temperature fluctuations during the measurement, while SPR needs thermostabilisation.