|Haofei Gong, Javier Garcia-Turiel, Krasimir Vasilev and Olga I. Vinogradova
Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany
The alternate deposition of polycations and polyanions on charged surfaces leads to a building up of films called polyelectrolyte multilayers. These films have received considerable attention during the last decade due to their potential applications in various fields, ranging from electroluminescent diodes to biomaterial coatings. We study here the adhesion properties, morphology, and growth of the DNA/PAH multilayers assembled on the glass surface. The main methods are Surface Plasmon Resonance Spectroscopy (SPR) and the Atomic Force Microscopy (AFM). The imaging was performed with commercial AFMS, while interaction and pull-off forces were measured with the home-made AFM-related setup. Regular oscillations in the pull-off force were observed for multilayers assembled both with and without drying. Strong adhesive forces were detected on the PAH surface of DNA/PAH multilayer. On the polyanion surface of DNA, the force-distance curves show repulsions on approach and weak attractions on retract. The SPR results show a nonlinear film growth at the first several layers, consistent with the pull-off force trends. AFM images show clear DNA loops on the surface of DNA and porous morphology on the surface of PAH. Our results are important for various applications, such biosensors, biochips, and more.