Sensor surface analysis
SPR sensors lack intrinsic selectivity: all refractive index changes in the evanescent field will be reflected in a change of the signal. These changes can be due to refractive index difference of the medium, e.g. a change in the buffer composition or concentration, also, non specific adsorption of material on the sensor surface can cause refractive index changes. To enable selective detection at an SPR sensor, its surface needs to be modified with ligands suited for selective capturing of the target compounds but which are not prone to adsorbing any other components present in the sample or buffer media. The sensor chips of IBIS Technologies show very low non-specific binding behavior.
Figure. Schematic representation of direct detection: the analyte is captured by the ligands (Y) immobilized in the hydrogel that matches the evanescent field. Accumulation of the analyte results in a refractive index change and in a shift of the SPR angle. In SPR terminology the ligand is immobilized (here in a hydrogel).