Do you know the history of SPR?

Surface Plasmon Resonance (SPR) is shorted for SPR which is a new technology developed from the 1990s. The interaction between ligand and analyte on biosensor chip has been detected by SPR principle which has been widely applied in various fields. In 1902, Wood discovered the SPR phenomenon for the first time in an optical experiment and made a simple record of it. But it wasn't until 1941, 39 years later, that a scientist named Fano actually explained the SPR phenomenon. Over the next 30 years, SPR technology has not developed substantially, nor has it been applied to practical applications. In 1971, Kretschmann laid the foundation for the structure of SPR sensor and began the experiment with SPR technology. In 1983, Liedberg first used SPRs for the reaction of IgG with its antigen and achieved success. In 1987, Knoll et al began to study SPR imaging. In 1990, Biacore AB developed the first commercial SPR instrument, which opened up a new movement for the wider application of SPR technology.

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In short, SPR is used for real-time analysis and monitoring between DNA and protein, between protein and protein, between drug and protein, between nucleic acid and nucleic acid, between antigen and antibody. Interactions between receptors and ligands and other biomolecules simple and quick. SPR has a wide range of applications in life sciences, medical testing, drug screening, food testing, environmental monitoring, drug testing and forensic identification.

Do you know the principles of SPR?

(I) Evanescent wave

According to the optical theorem proposed by French physicist Fresnel:

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It can be seen that when light is injected from the dense medium into the light thinning medium, the incident angle increases to a certain angle. So that the refraction angle reaches 90 °, the refraction light will disappear completely and only the reflected light will be left. This phenomenon is called total reflection. When the total reflection is studied from the angle of wave optics, it is found that when the incident light reaches the interface. And it does not directly produce the reflected light, but first passes through the light thinning medium at a depth of about one wavelength. Then it flows along the interface about half the wavelength and then returns to the dense medium. Waves passing through light-sparsely media are called evanescent waves.

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(II)  SPR optical principle

We mentioned earlier that when the light is reflected on the surface of the prism and the metal film, it forms the evanescent wave and enters the light thinning medium. If it is a metal medium, there is a certain plasma wave in the medium. Resonance may occur when two waves meet.

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When the evanescent wave resonates with the surface plasmon wave, the detected reverberation intensity will be greatly weakened. The energy is transferred from photon to surface plasma meanwhile most of the energy of incident light is absorbed by surface plasma wave, which reduces the energy of reflected light.

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We can see a minimal spike from the reflected intensity response curve on the left where shows the wavelength of incident light is resonant wavelength and its corresponding incident angle θ is SPR angle. The electron absorbs light energy so that the reflected light intensity is greatly weakened at a certain angle. The angle in which the reflected light disappears completely is the SPR angle. The SPR angle varies with the refractive index of the metal surface meanwhile the change of the refractive index is proportional to the molecular mass of the metal surface. Therefore, the specific signal of biomolecules interaction can be obtained by the dynamic change of SPR angle during biological reaction.

(III) Analysis of bio-molecular interaction based on SPR principle

Bio-molecular interaction analysis is a novel bio-sensor analysis technology based on SPR principle which doesn’t need for labeling or purification of various biological components. It is a process of interaction between a variety of biological molecules, such as peptides, proteins, oligonucleotides, oligosaccharides, and viruses, bacteria, cells, and small molecules, in real time and in real time, through a sensor chip. Surface plasma resonance is one of the important enhancement mechanisms of surface enhanced Raman spectroscopy. Because the size effect and quantum effect of noble metal nanoparticles can cause surface plasmon resonance by exciting light irradiation, Raman scattering signal is greatly enhanced to achieve the purpose of trace detection.

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Do you know the character of SPR?

After 20 years of development, SPR optical bio-sensor has become an important research tool in the field of life sciences and pharmaceuticals. Compared with traditional interaction techniques such as ultracentrifugation, fluorescence and calorimetry, SPR biosensors have the following remarkable characteristics:

1. Real - time detection. Dynamically monitor the whole process of biological molecule interaction.

2. The molecular activity was maintained without labeling the sample.

3. Very few samples are required and only 1 mg of protein is required for one surface.

4. The detection process is convenient and quick and the sensitivity is high.

5. It has a very wide range of applications.

6. High quality analytical data.

7. Track and monitor the stability of fixed ligands.

8. Quantitative determination of the complex does not interfere with the equilibrium of the reaction.

9. In most cases, there is no need to treat the sample.

10. Because the SPR is based on the measurement of the reflected light of the unpenetrated sample, it can be carried out in the opacity or even opacity.

Do you know the future of SPR?

As SPR technology becomes analytical biochemistry, the application of SPR bio-sensor will be more diversified in the field of drug development and food monitoring. Especially, its new application in the field of small molecule detection and lipid membrane will make the SPR bio-sensor more widely used in the future. It will play an increasingly important role on drug discovering and membrane biology. In recent years, its development has been particularly rapid. With the continuous improvement of SPR instruments and the continuous enhancement of bio-molecular membrane construction ability, SPR bio-sensors have a very broad application prospect. Because the SPR is based on the measurement of the reflected light of the unpenetrated sample, it can be carried out in the opacity or even opacity. However, compared with the traditional analytical methods, especially the immunoassay, the existing SPR sensing technology still has some shortcomings in the detection cost, ease of use, stability, detection efficiency and so on which also determines the main development trend of this technology in the next few years.