CONVECTION DURING INCUBATION OF MICROPLATE SOLID-PHASE IMMUNOASSAY - EFFECTS ON ASSAY RESPONSE AND VARIATION

In solid phase immunoassays, the incubation period is used to specific ally bind free analyte molecules of low concentration to immobilized c ountermolecules. Many of these assays use elevated temperatures during incubation, based on the assumption that the reaction thus is stimula ted by enhancing the association constant. In this paper we demonstrat e that elevated incubation temperatures are not likely to have any sig nificant effects on the association reaction. Furthermore we show that in many situations, uncontrolled thermally induced free convection pl ays an important role in mass transport of analyte toward the solid ph ase. Convection is a function of assay geometry and the properties of the materials used. Our experiments show that it is a major source of interassay variation which never before has been described in the cont ext of immunoassay incubation. Finally we define the conditions under which forced convection will improve assay response and reduce interas say variation. Applying forced convection during sample incubation of a two-step HBsAg assay, we obtained an increase in response rate per t ime unit by a factor of similar to 5. Interassay variation was reduced from 5-10% to 1-2%. Assay sensitivity improved by a factor of 2-6 wit hout the slightest modification in assay chemistry.