Rigid poly(methyl methacrylate) (PMMA) biochips directly modified with active protein spots were obtained, using a redox-initiated PMMA polymerization process. The protein immobilization mechanism is believed to be a combination of both a covalent binding through transient amino acid radical generation and a direct entrapment of the biomolecules in the PMMA polymer. Three different immunoassays (binding, capture, and sandwich) were performed using the developed system, and really promising limits of detection (160-200pg/mL) were obtained, demonstrating a novel straightforward route to fabricate plastic biochips.