Changes

SPR are oscillating electromagnetic waves of conduction electrons on the interface between a metal and dielectric. The conduction electrons have a resonant frequency at which they are excited, leading to these oscillations. As resonance is a requirement, only certain energies can excite the plasmons. This is done by matching the momentum of a Transverse Magnetic oscillation (polarised light) to the oscillation of the plasmons. When this coupling happens, SPR waves propagate along the surface of the metal film, gold in this case, and exponentially decays parallel to the surface.

As light coming from the medium of air cannot match the momentum of the plasmons by itself,

the SPR is only possible with a coupling mechanism: using a higher refractive index material on one side of the metal than the other. Prisms are commonly used as they have this higher index.

In this biosensor, the Kretschmann configuration is used.

A different concentration of adalimumab means a change in the refractive index of the analyte, leading to a change in the SPR excitation angle.

Optimisation of the optical setup can be done using several parameters such as the metal layer, the RI of the coupling materials (prism and substrate), focal length of focusing and collimating lens, and the length between the CCD detector and the final collimating lens.