Multilayer Fluorescent lmmunoassay

We describe a new multilayer immunoassay element for the determination of haptens in undiluted serum and plasma. Polysaccharide layers are coated onto a plastic base. The signal layer contains an immobilized antibody and a fluores-cent-labeled hapten. A second layer, containinga pigment, acts as an optical screen. Sample spreading is achieved by a molded grid in contact with the upper layer of the immu-noassay element. After sample is added to the element, endogenous analyte competes with the labeled hapten for the binding sites of the immobilized antibody; equilibrium is reached in 4.-12 mm. Because of the relative liquid-holding capacities of the layers and the grid, only a smallamountof the free components remains in the signal layer. The signal is measured by front-surface fluonmetry. This technology has been applied to theophylline and thyroxin assays. Within