Surface Plasmon Resonance

SPR is a phenomenon in which the reflected light disappears at a specific angle of incidence when light is incident on the side of the prism on which the gold thin film is placed. When biomolecules bind on the sensor chip, the surface refractive index changes and the angle of the reflected light shifts. Molecular interaction is monitored by acquiring sensorgrams that record this angle change in real time.

SPR measures the binding of various molecules such as antigen-antibody, protein, nucleic acid, carbohydrate, fat, cell, and virus.
In addition, label-free real-time analysis enables kinetic analysis of intermolecular association affinity (affinity) as well as
association rate constant and dissociation rate constant.

Applications of SPR in Life Science

​Yes/No: Checks whether or not there is a connection. The presence or absence of reaction can be checked by simply flowing the analyte (B)  to the sensor chip on which the ligand (A) is immobilized.
Screening: Multiple analytes can be run sequentially on the same ligand to evaluate which analyte binds best.
Concentration: After acquiring a sensorgram for each concentration of an analyte, a standard quantitation curve can be created through the concentration-signal graph.
Affinity: Evaluate the equilibrium constant after creating a Langmuir isothermal curve by acquiring the association section of the sensorgram for each concentration up to the equilibrium stage.
Kinetics: Evaluate the rate constants ka and kd through curve fitting by acquiring the association/dissociation section of the sensorgram  for each concentration.

Key Steps for SPR Analysis

1. Ligand Immobilization

The ligand immobilization step is the step of immobilizing the ligand on the surface of the sensor chip.
Substances used as ligands such as antibodies, proteins, nucleic acids, and peptides are very diverse.
Depending on the properties of the ligand material, the surface functional groups (COOH, Biotin, NTA) of the sensor chip and the immobilization method can be determined.

Immobilization with Amine coupling

2. Analyte binding and regeneration

​Analyte binding includes the association step in which the graph rises in real-time by injecting the analyte solution and binding to the ligand. By injecting only the running buffer, some analytes attached to the ligand are separated into the dissociation phase. After that, if the remaining analytes attached to the ligand are removed using a regeneration solution, experiments can be continued with different concentrations or different types of analytes on the same sensor chip.  The regeneration solution is a low pH buffer, high pH buffers, and solutions with high ionic strength can be selected and used according to the properties of the ligand-analyte.

3. Kinetic Evaluation

Kinetic parameters can be calculated through a sensorgram that observes association and dissociation sections by flowing different concentrations of analyte.
The association rate constant (ka) and dissociation rate constant (kd) are obtained through a 1:1 binding model.The equilibrium dissociation constant (KD) obtained by dividing the dissociation rate constant by the association rate constant can be used as a parameter to evaluate the bonding force between two molecules.