Surface plasmon resonance imaging (SPRI) is a high throughput optical biosensing technique used to study small molecules and provide data on the affinity, specificity, and kinetics of biomolecular interactions.

It is also referred to as surface plasmon resonance microscopy (SPRM) and provides its data by measuring the target molecules’ real-time binding association rates and dissociation rates. It is considered a fundamental principle behind many biosensor applications, diatom photosynthesis, and various lab-on-a-chip sensors.

Surface Plasmon Resonance (SPR) technology is combined with imaging devices to form SPRI and can be used in several different ways.

It is most commonly used to analyze molecular interactions because, unlike many other immunoassays, such as ELISA, SPR assays allow for real-time, label-free detection of biomolecular interactions and provide higher-throughput analysis than many traditional methods.

Surface plasmon resonance is also used for measuring the adsorption onto the surface of metal nanoparticles or onto a planar metal surface (such as gold or silver), as it is the basis behind many other tools that material adsorption onto planar metal. This includes using SPR as a characterization tool for lipid nanoparticles (LNPs) used in drug discovery.

Other SPR applications include observing protein-to-protein, protein-to-antibody, DNA-to-protein, and many other molecular exchanges. Unlike similar analytical techniques, SPR can be used to look at both binding kinetics and binding affinity.

A plasmon refers to the minimum amount, or quantum, of rapid oscillations of electron densities in conducting medium or plasma densities. Surface plasmon relates to this oscillation as it occurs on the surface of a conducting medium such as a metallic surface.

When polarized light hits an electrically conducting surface, such as a metal, some light is absorbed by the object’s surface electrons and resonates with the electrons along the material’s surface. Specifically, it occurs at the interface of the media with different refractive indices. These resonated electrons are the surface plasmons.

Surface plasmon resonance excites electrons on the surface of a conductive layer and detects the resulting oscillations of free electrons. This means that the excited electrons absorb some of the incident light, and the resulting reflected light will now contain an absorption line. This absorption line can then be used to determine various qualities of the material.