Get rid of ‘bulk effect’ and separate true binding without a reference channel!
Differences in liquid composition between samples and running buffer causes a change in refractive index, which in turn appears as a shift in the measured SPR curve. This is called bulk effect, and it is present with any method that records refractive index changes close to a sensor surface.
In traditional SPR, imaging SPR or localized SPR, meticulous bulk signal calibrations with multiple background solution injections and a dedicated reference channel are required to separate true molecular binding from the undesired bulk effect, and only small changes in concentrations of the solvent (e.g. DMSO) are allowed.
Bulk effect is not an issue with MP-SPR measurements, because the unique optical setup of MP-SPR instruments enables cross-correlation of parameters provided by the MP-SPR method and allows simple in line characterization of interfering bulk signal using the PureKinetics™ feature. This feature is available in all MP-SPR Navi™ instruments.
PureKinetics™ allows significant improvements, especially when a reference flow-cell is not available due to sample or sensor surface properties, or when high concentrations of additives (such as DMSO for solubility) are needed in the experiment. The method can be used to remove even 5% changes in the DMSO concentration from the sensogram without the need for multi-injection DMSO calibrations. PureKinetics™ improves remarkably small molecule detection as well as lipid bilayer or material-biomolecule interactions, where it is difficult to fabricate a reference channel for the experiments.