RSD Detection Principle

RSD detection principle
Surface plasmon resonance (SPR) immunosensor is an optical immunosensor that uses SPR technology to detect immune molecular reactions. Surface plasmon resonance occurs at the interface of two media with different dielectric constants. It is a charge density vibration generated by the interaction between the electromagnetic wave of the incident light and the charge density wave formed by the free electrons on the metal surface. This charge density wave propagating along the metal surface is called a surface plasma wave (SPW). Its amplitude inside the metal decays exponentially with the direction perpendicular to the surface. According to the Maxwell equation, the wave vector Ksp of SPW can be obtained:

Where εm is the dielectric constant of the metal, εa is the dielectric constant of the object being measured, ω is the angular frequency of the incident light, and c is
the wave velocity . When horizontally polarized incident light passes through a prism and irradiates the metal surface, the projection of the incident light wave vector on the X-axis is Kx:

εp is the dielectric constant of the prism, and θ is the angle of incidence. If the projection Kx of the incident light wave vector on the X axis is equal to the wave vector Ksp of the SPW, the incident light
will cause surface plasmon resonance
on the metal surface. Most of the energy of the incident light is absorbed by the SPW and converted into heat, causing the energy of the reflected light to drop sharply, and the minimum reflection intensity (i.e., resonance peak) can appear on the reflection spectrum. If the refractive index of the medium in contact with the metal surface or the dielectric constant of the object
being measured changes, the position of the resonance peak (resonance angle or resonance wavelength) will change. Therefore, by measuring
the change in resonance angle or resonance wavelength, information about the reaction of the object being measured on the interface can be obtained. Based on this principle, by modifying a layer of antibody molecules on the
reaction , when the antigen and antibody recognize each other, the position of the resonance peak will shift, and the magnitude of the shift will reflect
the amount of biological molecules fixed on the metal surface, thereby realizing immunoassay.