Surface plasmon resonance

What is surface plasmon resonance (SPR)?

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

How does SPR work?

In Biacore™ system SPR 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 recorded in real-time in a sensorgram. The schematic illustration below shows a sensorgram. The bars below the curve indicate the solutions that pass over the sensor surface.

Applications of Surface Plasmon Resonance

Biacore™ SPR systems are primarily used in:

• Biological research
• Biotherapeutics and small molecule drug discovery and development
• Vaccine development and quality control
• Epitope binning, potency, and immunogenicity studies
• Titer, concentration, and drug product release testing

Features of SPR

Surface Plasmon Resonance allows you to:

• Follow label-free molecular interactions in real-time.
• Perform analysis without labelled interactants/reporter molecules
• Analyze biological samples, complex mixtures or purified samples with no difference in data quality.
• Measure even weakly-binding molecules.
• Utilize low sample and reagent volumes with high precision.
• Reuse sensor chip surface saving time and cost

What kind of interactions can you study with SPR?

Biacore SPR systems can be used to study interactions involving any kind of molecule including:

• Organic compounds
• Proteins
• Nucleic acids
• Glycoproteins
• Viruses
• 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). There is no lower limit for organic molecules with modern Biacore SPR systems.

What samples can be used?

The SPR detection principle does not require labeling of any of the interactants. You can perform measurements on complex mixtures, such as:

• Cell culture supernatants
• Cell extracts
• Serum and plasma
• 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 clear, colored, or opaque samples with the same data quality.

How is surface plasmon resonance data displayed?

Your Biacore SPR data is displayed in real time via a sensorgram on the computer screen during an analysis. A sensorgram is a plot of response against time, showing the progress of the interaction. To monitor the interaction between two molecules, one molecule is attached to the sensor surface (ligand) and the other is free in solution (analyte).

What data can you obtain from an interaction?

The data from an interaction between two molecules 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.

Future trends and innovations in SPR

The drug discovery industry is in a great position with many new modalities and modes of action. Biacore SPR systems play a pivotal role in accelerating the development of advanced therapeutic modalities like proteolysis targeting chimera (PROTAC), antibody-drug conjugates (ADCs), and multi-specific antibodies.

As the demands on biophysical research grow, automation is essential for unlocking the full potential of SPR. By integrating advanced technologies—such as machine learning—modern platforms like Biacore systems can transform how researchers tackle challenges associated with SPR. These innovations streamline workflows, accelerate decision-making, and provide reproducibility, reliability, and scalability in therapeutic development.

Conclusion

Biacore systems monitor the interaction between molecules in real time using the phenomenon of surface plasmon resonance. Target molecules 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. Analysis can be done label-free with small sample quantities on complex mixtures or purified samples—with no difference in data quality. Your Biacore system SPR data is displayed in real time via a sensorgram on the computer screen during an analysis.

FAQs

Why is surface plasmon resonance important?

Biological processes are "real-time" events, driven and regulated by dynamic interactions between key molecules. End-point techniques such as ELISA offer a snapshot view of interactions. They only provide basic information such as overall binding strength (affinity). The affinity depends on the ratio of molecules on- and off-rates, which are time bound constants. Equal affinity interactions can have very different kinetic properties, resulting in different biological responses. These differences can't be resolved by viewing a point in time. SPR monitors molecular interactions in real-time so you can differentiate between variances in kinetic properties, even for interactions with challenging targets.

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".

What is shown on the sensorgram?

During sample injection, a positive response can be viewed in the sensorgram, as analyte binds to the ligand. 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.

Resources

 

1. Article: Boost your research with details on protein interaction
2. Handbook: Biacore™ Sensor Surface handbook
3. Selection tool: Biacore™ consumables selection tool
4. Courses: Free online learning tools
5. Infographic: Surface plasmon resonance (SPR) Visualize your research
6. Infographic: Biotin CAPture Kit Ready-to-go interaction analysis