Plasmon Resonance-Based Sensors Surface Plasmon

¶ … Plasmon Resonance-Based Sensors

Surface Plasmon Resonance-Based Biosensors

Surface plasmon resonance (SPR) was first observed in 1902 by Wood and this physical phenomenon has since begun to be used in multiple applications. Modern detectors now use the phenomenon to detect sub-monomolecular coverage. Since Wood came across the phenomenon, it has been perfected by Lord Rayleigh, Fano, Krestchmann and Raether. Actual sensors first came into use in 1983 by Liedberg. A good conceptual example is a polarized light being shone through a prism onto a sensor chip assembly with a film of thin metal on top. The shining of the light incites surface plasmons into becoming active and this phenomenon can then be measured. A wave-like oscillation of free electrons is induced and the intensity of the light is reduced in the process. The angle at which the maximum amount of refraction loss occurs is called the resonance angle [1].

Applications

Surface plasmon resonance can be used to determine the concentration of an analyte in a sample during a quantitative analysis session. The analysis involves a calibration curve whereby a response over time to an SPR series is plotted on a graph in the form of a curve. The amount of data points (dilutions) can range from 10 times to 100 or even 1000 iterations. The results of this analysis will depend a lot on the sample size [1].

The most significant benefit of using SPR detection is being able to determine the kinetics of bio-molecular reactions. The interactions of an analyte and a ligand immobilized on the sensor surface can be ascertained using SPR techniques and technology. Assessing and analyzing the process and results of such experiments is not terribly complex or beyond most people's understanding. It is enough to know that an optical method is used to measure the refractive index within proximity of a sensor surface [1].

History

Biosensor as a term was coined in roughly 1975 and its genesis related to the exploiting transducer principles for the direct detection of biomolecules on certain surfaces. One common example is a biosensor that measures glucose at the point of analysis. The science behind surface plasmon resonance advanced sharply in 1983 when physical methods for label-free real-time detection of biomolecules started to become possible [1].

Since then, more than two dozen countries have begun to use SPR technology en masse but it is impossible to reliably and accurately track all of the developments realized by those companies. The technology initially was more of a novelty with little to no real-world application but that has changed greatly over the years. One major update to its applications was the Evanescent Wave, which has become an integral and essential concept when discussing SPR sensing [1].

SPR Types