Homogeneous Fluorescentlmmunoassay with Dry Reagents

We describe an assay fortheophylline in serum in which the reagents for the substrate-labeled fluorescent immu-noassay procedurearecityreagentsIna paper matrix. This assay format is both rapid and convenient. In one such paper stripassay, the competingdrugconjugate Ispresent in the diluting buffer (dilution-into-conjugate strip assay); in another, all necessary assay reagents are containedon the strip (integral strip assay). The latter strip can be pre-pared by using appropriate solvents in a “two-dip ” pro-cedure, which prevents premature reaction of the assay constituents. The dilution-into-conjugate strip assays yield resultsthat compare well with those by the corresponding solution assay (r = 0.975, standard error of estimate = 1.67 mg/L) and by “high-performance ” liquid chroma-tography (r = 0.980, standard error of estimate = 1.4