SPR arises when photons are reflected from a conducting film at the interface between two media of different refractive indices. This phenomenon can be utilized by measuring a change in the angle of reflection of polarized near infra-red light on a gold surface, which occurs when the index of refraction of the surface changes. The Bio-Rad ProteOn XPR36instrument is used to measure biomolecular interactions, specifically the association rate and dissociation rate of analytes from a biomolecule immobilized on one side of a gold film. In the instrument, light is reflected on the opposite side of a gold film to excite the surface plasmons, that is, the oscillations of free electrons propagating along the film's surface. The angle of reflection of polarized light reflecting off this surface is measured. When the immobilized biomolecules are bound by their ligands, an alteration in surface plasmons on the opposite side of the film is created that is directly proportional to the change in bound, or absorbed, mass. The HTSRC hosts a Bio-Rad ProteOn XPR36instrument and can provide guidance and support in its use.
The technique of microscale thermophoresis allows for the detection of conformational changes in molecules that can be a consequence of binding, aggregation or polymerization, provided the change results in a change in mass, charge or solvation shell. The approach is well-suited for measuring equilibrium binding affinities. The technique requires the presence of a fluorophore and can be accomplished with small samples of analyte (8 uL). The HTSRC hosts aNanoTemper MST monolith 115 and can provide training and guidance in this simple technique.
Circular dichroism (CD) spectrometry measures very small differences in the absorption of right- and left-circularly polarized photons. This differential absorption correlates with the phenomenon of chirality. Changes in the CD spectrum correlate with protein secondary structure such as alpha-helixes or beta-sheets. Thus, CD spectrometry can be used to monitor changes in the secondary structure of biomolecules that possess chiral centers.