Hydrogen bonding between adenine-modified surfaces and terminal thymine-functionalized polystyrene: Influence of the surface adenine concentration on polymer recognition

The influence of the surface adenine concentration on the adhesion of terminal thymine-functionalized polystyrene (PS-thymine) to a silicon surface that was modified with adenine-functionalized triethoxysilane (ADPTES) was investigated. The surface adenine concentration was systematically varied via co-deposition of a non-hydrogen-bonding diluent. Two different silanes, i.e., 2-diphenylphosphinoethyl triethoxysilane (DPPETES) and 3-mercaptopropyl triethoxysilane (MPTES), were used as the diluents. The compositions of the silicon surfaces modified with different ratios of ADPTES/DPPETES were determined using X-ray photoelectron spectroscopy (XPS) and agreed well with the ADPTES/DPPETES molar ratios in solution. XPS and water contact-angle measurements revealed that modification of surfaces exclusively with the diluents or with a very low concentration of adenine did not result in significant PS-thymine attachment. However, as the adenine concentration on the surface increased, PS-thymine adsorption also increased, passing through a maximum before decreasing with a further increase in the adenine concentration. Surfaces modified exclusively with adenine showed negligible polymer attachment. A similar non-monotonic trend in PS-thymine adsorption was observed for surfaces that were modified with a mixture of ADPTES and MPTES, where PS-thymine adsorption was found to go through a maximum at a particular adenine concentration. A further increase in adenine concentration led to decreased polymer adsorption, and an exclusive presence of adenine was again found to promote negligible polymer adsorption.