#surface plasmon resonance

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What causes SPR signal increase?

In Surface Plasmon Resonance, signal intensity increases when soluble analyte specifically binds to ligand immobilized on the sensor surface, thereby increasing mass concentration and local refractive index within the evanescent field approximately 300 nm from gold film. This accumulation shifts resonance angle, recorded as increase in resonance units over time during association phase. Dissociation or buffer washing decreases signal. Evaporation, light absorption, or refractive index decrease would lower or destabilize signal rather than increase it. Specificity is validated using reference flow cells and concentration series for accurate kinetic characterization.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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In SPR, the ligand is:

In Surface Plasmon Resonance terminology, ligand refers to the molecule permanently attached to the sensor chip dextran matrix, while analyte is the soluble partner that flows in microfluidic channels. Immobilization is typically achieved via amine, thiol, or streptavidin coupling, ensuring stable baseline and reproducible orientation. Ligand density influences response magnitude and kinetic accessibility. Analyte binding to ligand produces resonance unit increase. Distinguishing ligand and analyte is crucial for kinetic modeling, since immobilization restricts diffusion and may affect binding activity. Antibody coating or bead systems are not used in conventional SPR sensor design.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Which physical property does SPR detect?

Surface Plasmon Resonance detects minute shifts in refractive index at the sensor chip interface, which directly correlate with mass concentration variations close to the gold surface. When light excites surface plasmons, resonance occurs at a specific angle dependent on the dielectric environment. Adsorption or binding of biomolecules increases the refractive index within the evanescent field, shifting the resonance angle. This optical readout is independent of magnetic or pH changes and does not measure bulk optical density alone. Sensitivity to refractive index enables quantitative, real-time monitoring of unlabeled interaction kinetics and equilibrium binding parameters.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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SPR is used to study:

Surface Plasmon Resonance is a powerful label-free technique for monitoring biomolecular interactions in real time without fluorescent or radioactive tags. One interaction partner is immobilized on a gold-coated sensor chip while the other flows over the surface. Binding changes the refractive index near the surface, altering the resonance angle proportionally to mass accumulation. This allows determination of association and dissociation rate constants, affinity, and specificity. Applications include protein-protein, protein-DNA, antibody-antigen, and small molecule screening. Traditional processes like DNA replication, transcription, and translation are studied by other molecular biology techniques.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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What does SPR stand for?

SPR stands for Surface Plasmon Resonance, a physical optical phenomenon occurring at the interface of a thin noble metal film, typically gold, and a dielectric medium. Upon illumination with p-polarized light under conditions of total internal reflection, conduction electrons undergo collective oscillations called surface plasmons. The resonance angle is highly sensitive to refractive index changes near the metal surface. Biomolecular binding increases local mass and refractive index, shifting resonance. This principle enables real-time, label-free detection of biomolecular interactions and is extensively used in biosensor technology for kinetic analysis.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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