By Anna Moberg, Staff Research Engineer, Cytiva

What is surface plasmon resonance?

Surface plasmon resonance (SPR) allows you to perform analysis of molecular interactions in real-time.
SPR occurs when polarized light strikes an electrically conducting surface at the interface between two media. This generates electron charge density waves called plasmons, reducing the intensity of reflected light at a specific angle known as the resonance angle, in proportion to the mass on a sensor surface.

Biacore™ SPR systems are used primarily in pharmaceutical development, quality control, and basic life science research.

Follow label-free molecular interactions in real-time

In Biacore™ assays, target molecules, most frequently proteins are immobilized on a sensor surface and a sample containing a potential interacting partner in solution is injected over the surface through a series of flow cells.

During the interaction, polarized light is directed toward the sensor surface and the angle of minimum intensity reflected light is detected. This angle changes as molecules bind and dissociate and the interaction profile is thus recorded in real-time in a sensorgram.

What kind of interactions can you study with SPR?

You can use Biacore™ systems to study interactions involving (in principle) any kind of molecule, from organic compounds to proteins, nucleic acids, glycoproteins, and even viruses and whole cells. Since the response is a measure of the change in mass concentration, the response per molar unit of interactant is proportional to the molecular weight (smaller molecules give lower molar responses).

What’s more, you will find that there is no lower limit for organic molecules with today's Biacore™ systems.

What samples can be used?

The SPR detection principle does not require labeling of any of the interactants and you can perform measurements on complex mixtures, such as cell culture supernatants or cell extracts, as well as purified interactants. The identity of the interactant monitored in a complex sample matrix is determined by the interaction specificity of the partner attached to the surface. The SPR detection principle is noninvasive and you can analyze equally well on clear, colored, or opaque samples.

How is surface plasmon resonance data displayed?

Biacore™ systems monitor the interaction between two molecules, of which one is attached to the sensor surface and the other is free in solution. A sensorgram is a plot of response against time, showing the progress of the interaction. This curve is displayed for you directly on the computer screen during an analysis.

What is shown in the sensorgram?

During sample injection, a positive response can be viewed in the sensorgram, as analyte (the interacting partner in solution in Biacore™ based assays) binds to the ligand (the interaction partner that is attached to the sensor surface in Biacore™ based assays). The response decreases during dissociation. After an analysis cycle is completed, regeneration solution is passed over the sensor chip, removing bound analyte, preparing for the next analysis cycle.

The schematic illustration below shows a sensorgram. The bars below the curve indicate the solutions that pass over the sensor surface.


What data can you obtain from an interaction?

The data from an interaction is presented in a sensorgram, providing you with quantitative data on:

  • Binding
    Does the interacting partner bind to the target molecule?
  • Specificity
    To what extent does an interacting partner cross-react with other molecules?
  • Concentration
    How much of a given molecule is present and active?
  • Kinetics
    What are the rates of association and dissociation?
  • Affinity
    How strong is the binding?

Get an overview of analysis and interpretation of SPR data in our comprehensive library of Application guides

How do I interpret a sensorgram?

The shape of the sensorgram gives information about the interaction.

A few examples of how to interpret sensorgram shapes are described in the application guide “Affinity and Kinetics measurements”.