SPR allows the kinetic parameters of the molecular interaction to be determined, but it is also used for quantitative kinase inhibitor Axitinib purposes, i.e. for the determination of unknown concentrations of analytes in complex samples. The significant advantage over other biophysical approaches is that the interaction is studied in real time and without the need of labelling. The method is very sensitive, as concentrations in the picomolar range may be determined. The limit for the detection is around 200 Da, depending from the instrument used. Smaller molecules may also be detected with competition type assay or by including one or more amplification steps, which lowers the sensitivity of detection to femtomolar levels . Finally, the technology can be included in portable instruments [18�C20].
Field detection is desirable in Inhibitors,Modulators,Libraries monitoring and identification of biological agents as well as environmental pollutants. The portable SPR platforms were among other included in detection of ricin , enterotoxin B , 2,4-dichlorophenoxyacetic acid  and atrazine .Biosensors based on SPR utilize a thin metal film between two transparent media of different refractive index, e.g. a glass prism and sample solution. Gold is preferably used in many SPR refractometers. A plane-polarized Inhibitors,Modulators,Libraries light beam entering the higher refractive index medium (glass prism) can undergo total internal refraction above a critical angle of incidence. Under these conditions, an electromagnetic field component of the light, the evanescent wave, will penetrate into the gold film.
At a specific angle of incidence, interaction of this wave with free oscillating electrons at the gold film surface will cause the excitation of surface plasmons, resulting subsequently in a decrease in the reflected light intensity. This phenomenon is called surface plasmon resonance Inhibitors,Modulators,Libraries and occurs only at a specific angle of incident light. SPR system thus detects changes in the refractive Inhibitors,Modulators,Libraries index of the surface layer of a solution in contact with the sensor chip (Figure 1A).Figure 1.(A and B) The angle of the minimum of reflected intensity shifts when one molecule binds to the other one attached to the surface of the gold layer and, therefore, changes the refractive index of solution. In the SPR biosensor terminology the molecule …SPR is observed as a sharp dip in reflected intensity at a certain angle, which is dependent on the refractive index of the medium on the non-illuminated side of the surface.
This angle shifts when biomolecules bind to the surface and change the refractive index of the surface layer Batimastat (Figure 1B). The sensorgram is a plot of the SPR angle against time, and displays the real-time progress of the interaction at the sensor surface (Figure 1C). Most of the SPR biosensors utilize response units (RU). The signal is proportional to the amount of the bound molecule (Figure 2). For proteins it was estimated that approximately selleck bio 1,000 RU corresponds to surface coverage of 1 ng/mm2 .