A sample processing assembly for treatment of a sample on a substrate includes a mounting surface for the substrate and a closure body configured to releasably retain a cover member. The closure body is movable between an open position and a substantially closed position. When a substrate is placed in the assembly and the closure body is in the substantially closed position while retaining a cover member, a reaction chamber is formed for processing a sample. A cover member for use with the sample processing assembly is also provided.
