Matrix: carboxymethylated dextran covalently attached to a Gold surface. Molecules are covalently coupled to the sensor surface via amine, thiol, aldehyde or carboxyl groups. Interactions involving small organic molecules, such as Drug candidates, through to large molecular assemblies or whole viruses can be studied. A high binding capacity gives a high response, advantageous for capture assays and for Interactions involving small molecules. High surface stability provides accuracy and precision and allows repeated analysis on the same surface.