Fluid Chamber Membrane

A new format for solid-phase immunoassays has been developed in which a monoclonal antibody-coated membrane, incorporated into a cylindrical, disposable device, regulates sample and reagent delivery. We illustrate the method with a two-site, immunoenzymometnc assay that can detect human choriogonadotropin at less than 50 mt. units/L (4 pg/L) in urine and less than 25 mt. units/L (2 j.tg/L) in serum and takes less than 5 mm to perform. The solid-phase antibody is located in a circular area in the center of the membrane so that in the presence of the hormone, after addition of substrate, a blue enzyme product is generated in this circular area. The high ratio of surface area to volume within the microporous matrix of the membrane assures short diffusion distances and therefore rapid binding of liquidphase reagents to the solid phase. Pseudo-first-order reaction kinetics describe the binding of antigen to immobilized antibody and the binding of enzyme-labeled antibody to immobilized antigen. The speed and simplicity of this format may facilitate testing for many analytes, both soluble and particulate, as well as serological testing.