How to get rid of bulk effect in SPR measurements? • How to separate true binding of small molecules from DMSO effect? • Can any SPR method tolerate even 5% changes in DMSO concentration during runs? • How to determine bulk effect without a reference channel? 

What is bulk effect?

Bulk effect (sometimes called DMSO effect or solvent artefact) is the difference in liquid composition between samples and running buffer. The composition difference is seen as a change in refractive index, which in turn appears as a shift in measured SPR curve. In traditional SPR, imaging SPR or localized SPR, only part of the SPR curve can be seen and therefore, several steps have to be taken in order to separate true molecular binding from the undesired bulk effect.

How to get rid of bulk effect in SPR measurements?

Bulk effect is always present when optical methods are used. Traditionally, for instance in Biacore measurements, imaging SPR or localized SPR, bulk effect is distinguished from binding with meticulous bulk signal calibration requiring multiple background solution injections. However, this linearization method allows only small changes in concentration of the solvent (e.g. DMSO) and requires a dedicated reference channel during measurements.

How to get rid of bulk effect in MP-SPR measurements?

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 PureKinetics feature. This feature is available in all MP-SPR Navi™ instruments.

(picture on the left) Measurement of adalimumab (known as Humira®) affinity to FcyIIb and IIIb in crude samples containing more than 10cells/mL was compared to affinity in purified end product. Affinity of purified end product was the same before (black) and after (red) the measurement of crude sample (blue). Binding in crude sample was only slightly weaker. Some differences in the affinity was expected due to difference in the pH of the cell growth media compared to buffer.


Why is PureKinetics the best choice?

  • No reference channel needed
  • Tolerates even 5% changes in DMSO concentration
  • Does not require multiple DMSO injections for calibration

When is PureKinetics useful?

  • Kinetic measurements of small molecules
  • Interaction measurements with lipid bilayers
  • Material interactions with biomolecules
  • Material interactions with solvents


PureKinetics™ allows significant improvement especially when reference flow cell is not available due to sample or sensor surface properties, or when high concentrations of additives (such as DMSO for solubility) is needed in the experiment, but the target protein does not tolerate them well. The method can be used to remove even 5% changes in the DMSO concentration from the sensogram without 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.

(A) the standard SPR sensogram and (B) the PureKinetics™ sensogram of the same experiment. Measurements were done in parallel (blue and green). The standard SPR sensogram shows large responses due to the refractive index differences (bulk effect) between running buffer and dissociation or regeneration solutions. The PureKinetics™ sensogram shows the true binding response without bulk artefacts. Using the PureKinetics™ feature, the IgG dissociation in changing buffers could be quantified.
Events in the sensogram: 1. dissociation buffer PBS + 1 M NaCl, 2. IgG 33 µg/mL, 3. dissociation buffer PBS + 1 M NaCl 4. and 5. regeneration solution glycine/HCL pH=2.0


To summarize, if you are after high quality kinetic data, contact us

Click here to see application examples. You can also read more about PureKinetics™ in AN#147 and about measurements in 100% serum in AN#151.