The underlying physics of the principles of SPR are complicated. To allow the detection of an interaction one molecule termed by BIAcore as the ligand is immobilized onto the sensor surface. Its binding partner termed by BIAcore as the analyte is then injected in aqueous solution ideally with the same components and composition as the running buffer through the flow cell, under continuous flow. As the analyte binds to the ligand the accumulation of protein on the sensor surface causes an increase in refractive index.
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The underlying physics of the principles of SPR are complicated. To allow the detection of an interaction one molecule termed by BIAcore as the ligand is immobilized onto the sensor surface.
Its binding partner termed by BIAcore as the analyte is then injected in aqueous solution ideally with the same components and composition as the running buffer through the flow cell, under continuous flow. As the analyte binds to the ligand the accumulation of protein on the sensor surface causes an increase in refractive index. This refractive index change is measured in real time sampling in a kinetic analysis experiment is taken every 0.
This background response must be subtracted from the sensorgram to obtain the actual binding response. One RU represents the binding of 1 pg of protein per square mm. To get round this technical difficulty, BIAcore sensor chips have a - nm thick carboxymethylated dextran matrix attached.
However, having very high levels of ligand immobilised on the surface has two important implications for the technique. Such high ligand density may result in the rate at which the surface binds the analyte exceeding the rate at which the analyte can be delivered to the surface this latter consideration is referred to as mass transport. If this condition arises, mass transport becomes the rate-limiting step, and as a consequence, the measured apparent on-rate will be slower than the true on-rate.
A related problem is that, following dissociation of the analyte, it can rebind to the unoccupied ligand before diffusing out of the matrix and being washed from the flow cell. Consequently, the measured apparent off-rate is slower than the actual off-rate. The SPR optical unit consists of a source for a light beam that passes through a prism and strikes the surface of a flow cell at an angle, such that the beam is totally reflected.
Under these conditions, an electromagnetic component of the beam, the evanescent wave, propagates into the aqueous layer and can interact with mobile electrons in the gold film at the surface of the glass. At a particular wavelength and incident angle, a surface plasmon wave of excited electrons the plasmon resonance is produced at the gold layer and is detected as a reduced intensity of the reflected light beam.
In Biacore instruments, monochromatic light in the shape of a wedge a broad distribution of incident angles is used. The optical device has no moving parts and the fixed geometry enhances stability and allows binding to be monitored in real time. The SPR angle is sensitive to the composition of the layer at the surface of the gold. A baseline SPR angle is first determined by washing buffer over the surface with a fixed amount of ligand attached.
To this flow of buffer, some analyte is then added. The binding of analyte to immobilized ligand causes an increase in the refractive index at the surface, thereby changing the SPR angle because it is directly proportional to the amount of bound analyte. The exact relation between RU and ng of material bound will vary with the refractive index of the analyte. If the added molecule does not bind to a target or receptor, the SPR angle change in the sample and reference flow cells will be the same, and, after subtraction, will give a zero net RU response that indicates no binding occurred.
Only bound protein generates a positive SPR signal and that signal, recorded over time, produces a sensorgram.
EMBL - European Molecular Biology Laboratory
Product Support Biacore T is a versatile system for high-quality characterization of molecular interactions, from ions to viruses. One platform for comprehensive characterization of molecular interactions in terms of kinetics, affinity, specificity, comparability, concentration, immunogenicity, and thermodynamics Reliable ligand-binding assays, even for the most complex biologics Confident selection and characterization of the smallest organic compounds to large multidomain proteins Validated software meeting your regulatory expectations by supporting GxP procedures and 21 CFR Part 11 compliance Fast, simple kinetic analysis Biacore T software offers a range of tools for confident and reliable kinetic analyses. These analyses can be performed using a multicycle approach many samples against one ligand or when different ligands are immobilized , or alternatively, using singlecycle kinetics fast runs without regeneration. Read more Confident concentration analysis — with or without standards Software-supported direct binding and inhibition assays enable measurement of active concentration. The precision and automation of the system generates highly reproducible data. Calibration-free concentration analysis CFCA is of great value when no satisfactory calibration standard is available. Secure assays to meet regulatory needs The widely adopted Biacore T offers reliable ligand-binding assays—as described in regulatory guidelines—to characterize and assess comparability, even for the most complex biologics.
EMBL - European Molecular Biology Laboratory
BIACORE T200 SPR Biosensoren