Abstract: An assay method comprising the step of binding a second substance to a first substance immobilized to a solid phase surface, the first substance being either a ligand or a species bound directly or indirectly thereto. The method is characterized in that the solid phase surface having the first substance immobilized thereto exhibits and electric charge, and that the reaction for binding the second substance to the first substance is performed at an ionic strength below 100 mM, and at such pH conditions that the electric charge of the second substance is opposite to that of the solid phase surface so that the second substance is electrostatically attracted by the solid phase surface to be concentrated thereto.

Abstract: In assays of the type which comprise contacting the sample containing the analyte to be detected with a solid phase surface supporting a ligand capable of binding the analyte, undesired binding to the surface is prevented to a substantial degree by adding to the sample one or more components of the material forming the ligand supporting solid phase surface, which components are in at least partially soluble form and capable of interacting with constituents of the sample medium.

Abstract: Methods for functionalizing sensing surfaces to be used in systems for measuring simultaneously several properties of one biomolecule as well as for simultaneously measuring the concentrations of a plurality of biomolecules in a sample. The invention furthermore also relates to sensor units containing such surfaces, to the use thereof for surface characterization of biomolecules, and to a reagent kit for functionalization of sensing surfaces.