SPR is an optical phenomenon occurring naturally when light undergoes total internal reflection at the interface between a prism and a metal film, generating an evanescent wave that penetrates into the rarer medium. If the medium (commonly a noble metal) supports a plasmon wave, resonance may occur between the two wave modes under energy conservation conditions. SPR technology applies this classical optical phenomenon to develop a biosensing approach for analyzing biomolecular interactions. By observing the interactions between ligands and analytes immobilized on a biosensor chip, changes in the resonance angle (SPR angle) of polarized light at the critical angle between two media of differing refractive indices can be monitored. Resonance leads to significant attenuation of reflected light, and at a specific incidence angle, complete disappearance of reflected light can be observed. Dynamic monitoring of SPR angle changes during a biological reaction yields specific signals reflecting molecular binding and interactions.

Schematic diagram of Surface Plasmon Resonance (SPR) principle

Compared with conventional affinity measurement methods, SPR offers the following advantages:

1. No purification or labeling is required for any molecules during measurement.

2. Real-time monitoring of the dynamic reaction process.

3. Rapid acquisition of results, ensuring high work efficiency.

4. Higher sensitivity in measuring low-affinity antibodies.

We can provide SPR measurements for various sample types, including but not limited to small molecules, proteins, nucleic acids, lipids, bacteria, viruses, and whole cells. Multiple types of biomolecular information can be provided, including binding specificity, concentration analysis, kinetics and affinity analysis, as well as thermodynamic data.

SPR affinity measurement is also applicable to qualitative studies for confirming interaction specificity. It can monitor many sequential binding events, as each individual event results in a mass increase on the sensor chip surface, and all stages of the binding process are monitored. Examples include epitope mapping, antibody isotyping, and immunogenicity measurement.

Most chemical and spectroscopic methods for quantifying proteins (1) measure total protein content and (2) cannot distinguish between active and inactive molecules, nor can they be applied directly to unpurified samples. Since SPR is a non-invasive method (no light penetration through the sample), it can measure small amounts of analyte molecules from complex matrices, such as food, serum or plasma, and cell extracts. Both direct and indirect (inhibition or competition) methods are feasible for concentration measurement. SPR biosensors are particularly suitable for measuring kinetic association and dissociation rate constants through real-time monitoring of binding interactions.

Figure 2 SPR sensor surface adsorption of bovine serum protein

-- Stable performance. In specific application scenarios, such as when proteins are particularly valuable, affinity data obtained are generally high.

-- For many small molecules, stringent buffer conditions are required, and sensor chips are relatively expensive.

-- Professional technical team with extensive experience.

-- High measurement efficiency, label-free and real-time monitoring.

-- Advanced instrumentation.

-- Broad application range: suitable for protein, nucleic acid, polypeptides, and nanomaterial interaction analysis.

-- One-stop service: providing integrated solutions from affinity measurement to molecular interaction studies.