Transparent flow through membrane for dry reagent analytical devices

A test device for colorimetric determination of an analyte in a test fluid which device comprises a dry reagent layer containing a hydroperoxide and a redox dye capable of colorimetrically detecting the presence or concentration of the analyte which dry reagent layer is overcoated with a transparent, fluid permeable, swellable membrane comprising a blend of an aqueous based dispersion of water dispersible polyurethane together with water soluble polyethyleneoxide, polyvinylpyrrolidone or polyvinylalcohol wherein the transparent, fluid permeable, swellable membrane has immobilized therein an anti-fluorescein antibody and contains a first mobile anti-analyte antibody bearing fluorescein and a second mobile peroxidase labeled anti-analyte antibody together with copper bonded to a charged polymer as a capture reagent for creatinine in the test fluid, so that when the analyte is present in the test fluid there is formed a fluorescein labeled anti-analyte antibody/analyte/peroxidase labeled anti-analyte antibody sandwich in which the fluorescein and peroxidase are available for further reaction and are captured by interaction with the immobilized anti-fluorescein antibody, so that analyte in the test fluid will prevent the peroxidase labeled anti-analyte antibody from flowing through the transparent, fluid permeable, swellable membrane to the dry reagent layer and, in the absence of analyte in the test fluid, the peroxidase labeled anti-analyte antibody will flow through the transparent, fluid permeable, swellable membrane to the dry reagent layer where the peroxidase from the peroxidase label on the second anti-analyte antibody can react with the hydroperoxide and redox dye to colorimetrically detect the analyte wherein the intensity of the color formed by the colorimetric determination reaction is in an inverse relationship to the concentration of the analyte in the test fluid.