Surface Plasmon Resonance (SPR)

So far, I have been talking about LSPR, which comes up in UV/Vis. What is LSPR?

Surface Plasmon Resonance (SPR)

SPR is restricted to flat surfaces with metal-dielectric interfaces; typically gold or silver films. A dielectric is a non-conduction material that can be polarized by the electric field. Common dielectrics in SPR are air, vacuum, water, buffer solutions, glass, biological materials, polymers.

Biosensing with SPR

Surface Plasmon Resonance (SPR) is widely use for studying interactions at metal-dielectric interfaces, particularly in bio sensing applications.

In the setup below, light hits a gold film through a prism at specific angles. Binding events on the gold surface change the refractive index, shifting the resonance angle.

What you measure: Shift in angle of minimum reflectance

Glass prism
    |
Gold film (metal) ← 50 nm thick
-----------------  ← This is the interface where plasmons propagate
Sample solution (dielectric)

Some applications are antibody-antigen binding, drug-target interactions.