We demonstrate a novel technique for molecular imprinting and immobilization on a surface of a polymer containing azo dyes (azopolymer). The azopolymer was found to be capable of immobilizing micrometer- and nanometer-scale macromolecules (e.g., lambda-DNA, immunoglobulin G (IgG), bacterial protease, and 1-mum polystyrene particles) through photoirradiation with blue-wavelength light. Fluorescence and atomic force microscopy studies revealed that the azopolymer surface deformed along with the shape of the macromolecules, holding them in place after photoirradiation. The desorption of the immobilized macromolecules from the azopolymer surface in an aqueous medium was observed to be very slow, on the time scale of 10 min to weeks, depending on the photoirradiation time. Immunological and enzymatic studies showed that IgG and bacterial protease immobilized on the azopolymer surface retained their original functionality. These results suggest that the azopolymer physically, not chemically, binds the macromolecules because of the increase in contact area between the macromolecules and the azopolymer surface after photoirradiation.

A photo-immobilization based process is presented for direct imaging of hierarchical assemblies of biopolymers using atomic force microscopy (AFM). The technique was used to investigate the phase behavior of F-actin aggregates as a function of concentration of the divalent cation Mg2+. The data provided direct experimental evidence of a coil-on-coil (braided) structure of F-actin bundles formed at high Mg2+ concentrations. At intermediate Mg2+ concentrations, the data showed the first images of the two-dimensional nematic rafts discovered by recent x-ray studies and theoretical treatments.

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.

The construction of a soft flash x-ray (FX) apparatus with a new type of FX tube for biomedical use is described. The FX apparatus may be used for condenser charging voltages of 50–90 kV and peak currents of 20–40 kA. The electric pulse width of the FX waveforms was almost constant and its value was about 0.3 μs. The effective focal spot varied according to the condenser charging voltage, the anode–cathode (A–C) distance, etc., ranging from 0.2–3.0 mm in diameter. We selected two combinations of electrodes: (a) for normal focusing and a high dose rate; (b) for fine focusing and a low dose rate. The FX intensity was determined by the condenser charging voltage and the A–C distance, while the FX quality (average spectrum distribution) was determined by the average voltage of the FX tube and insertion of metal filters. The average voltage of the FX tube varied according to the condenser charging voltage and the A–C gap impedance. Various clear FX images were obtained by controlling the FX intensity, quality, and the focal spot size. We used Fuji Computed Radiography (FCR) in conjunction with our FX radiography, and by controlling the FX quality and the focal spot size, we obtained some interesting biomedical radiograms.

In our photo-induced immobilization technique for an antibody (IgG) using azopolymers, the introduction of COOH and NMe(2) into the azopolymers, which can introduce surface charges, strongly affected the immobilization properties such as the efficiency of immobilization and the activity of the immobilized IgG (i.e., the orientation of the immobilized IgG). The introduction of COOH promoted a more active orientation of the immobilized IgG. The orientation was determined during the adsorption process onto the azopolymer surface in solution before photo-immobilization, and was maintained during the photo-immobilization. The surface charge of the azopolymer appears to be an important factor for IgG orientation, which involves electrostatic interactions between its Fab and the azopolymer surface.