VISCOSIMETRIC AFFINITY ASSAY

Affinity ligands and/or affinity receptors may be quantified by a visc osimetric assay which can be carried out with a simple technique and h as the potential of broad applications. The viscosimetric affinity ass ay is based on the high contribution of affinity bonds to the viscosit y of an aqueous dispersion of a hydrocolloid that is bearing affinity ligands. In dispersions of such sensitive hydrocolloids at a concentra tion above the overlapping point, agglutination is not possible and th e modulation of viscosity by the formation or dissociation of intercol loidal affinity bonds may be several orders of magnitude larger than t he basic viscosity measurable in the absence of intercolloidal affinit y bonds. If dispersions (30 g liter(-1)) of branched dextran with high molecular weight were used as reagent for concanavalin A (Con A), the Con A concentration necessary for a significant rise in viscosity was decreased with increasing colloid size. The viscosity of dispersions containing both a ligand-bearing high-molecular-weight dextran and an appropriate polyvalent receptor protein (lectin or antibody) showed a dependence on the concentration of free ligands (sugars or insulin) ac cording to the law of mass action. In this competitive mode the viscos imetric affinity assay seems to be well adaptable to many analytical p roblems. (C) 1996 Academic Press, Inc.