Working group of Prof. Gauglitz
Surface modification
The detection of binding events on substrate surfaces requires special surface modification to provide a stable and homogenous surface with a defined concentration and good accessibility of the immobilized components. The modification of the substrate depends on the application area. First, in label-free detection method, it is necessary to prevent non-specific binding, as every binding event to the surface is detected. Second, through surface modifications it is possible to tune the numbers of available binding sites. This is important concerning the type of assay or the application. Polymers like poly-(ethylene)-glycol (PEG) or aminodextran (AMD) are widely used for surface modifications but have different characteristics. PEG forms polymer brush at the surface which is a more homogeneous surface structure whereas AMD forms a hydrogel layer providing more binding sites compared to PEG. Both polymers are coupled covalently on the surface.
The next step contains the immobilization of ligands, which finally interact with the analyte. The ligands can be coupled covalently on the biopolymer using active-ester chemistry or via affinity binding like streptavidin/biotin. Furthermore for characterization of kinetic and thermodynamic reactions (determination of dissociation/ association and affinity constants) the surface has to be regenerable after binding reaction, without losing their properties. But e.g. for clinical assay single chip measurements are preferred so that one has to assure a high chip to chip reproducibility.