Photoinduced immobilization of biomolecules on the surface of azopolymer films and its dependence on the concentration and type of the azobenzene moiety

We report on the photoinduced immobilization of Immunoglobulin G (IgG) on the surface of azobenzene-bearing acrylate copolymers (azopolymers). Two different types of azopolymers were synthesized that incorporated either a 4-aminoazobenzene moiety (H-azopolymer) or a 4-aminocyanoazobenzene moiety (CN-azopolymer), using different concentrations of the respective moieties. IgG was immobilized on the surfaces of the azopolymer films by exposure to visible light, and each of the films was then treated with an aqueous solution of an antigen. Antigen-antibody reactions were confirmed on the surfaces of the films, indicating that immobilized IgG generated by a photoirradiation can retain its activity. The amount of the immobilized antibodies on the azopolymer surfaces increased with azobenzene content up to 30 wt % and saturated over 30 wt % when measured under the same conditions. The efficiency of the immobilization process was found to correlate with the depth of deformations on the surfaces of the azopolymers, which were characterized by comparison with deformations induced by polystyrene microspheres under the same conditions. The increased contact area produced by photodeformation could enhance the interactions between the antibodies and the azopolymer, thereby causing the antibodies to be more firmly immobilized. However, the photoimmobilization of IgG on H-azopolymers was superior to that on CN-azopolymers, even though their original hydrophilicities and adsorption efficiencies were almost the same. We confirmed that both the photoisomerization processes and retention rates of the immobilized antibodies were different for H- and CN-azopolymers. This suggests that the effectiveness of photoimmobilization is controlled not only by photodeformation but also by retention capability, which in turn depends on the chemical structure after photoirradiation.