Cassette bodies for use with electrophoresis apparatus can be formed of a single piece of molded or machined plastic. Such cassette bodies can include a plurality of channels that pass through the cassette body, from a proximal end to a distal end. Such channels can be defined by upper and lower chambers. The upper chambers can be in fluid communication with a first buffer pool through a semi-permeable membrane, and the lower chambers can be in fluid communication with a second buffer pool. An electric current can be passed through the first and second buffer pools, and then reversed, to perform an electrophoresis operation that can separate a biomolecule of interest from free probes, and provide for convenient collection of said biomolecule of interest.