Abstract: An improved polymer device for conducting a multiplicity of individual and simultaneous binding reactions or performing other separation techniques is described. The apparatus comprises a polymer substrate on which are located discrete and isolated sites for such reactions or separation phenomena. The apparatus is characterized by discrete and isolated regions that extend through said substrate and terminate on a second surface thereof such that when a test sample is allowed to the substrate, it is capable of penetrating through each such region during the course of a reaction. The use of castable polymer techniques improves the manufacturing flexibility and cost over prior materials and fabrication methods and also provides certain improved properties such as lower specific stiffness and ease of lamination or bonding to other elements of a device.