Abstract: A solid phase binding member for the detection of an analyte in a test sample is described. The binding member comprises: (1) a solid support having micropores; (2) a polymer reversibly water-soluble before its application to the solid support; and (3) a ligand covalently attached to the polymer, the ligand interacting specifically with the analyte. The solid support can have micropores throughout or on its surface, and can be rayon, paper, fabric, plastic, agarose or polyacrylamide beads, glass, microcrystalline cellulose, or acid-treated plastic. The polymer can be carrageenan or sodium alginate. The ligand can be an antibody, a univalent antigen-binding fragment of an antibody, an antigen, a hapten, an enzyme, a hormone, or a single-stranded nucleic acid. Methods of use of the binding member are also described involving incorporation into a test device. The test device can be a dip stick, a hollow vessel, a slide, or a porous bead.