A dendron having nine carboxylic acid groups at the end of the branches and a protected amine at the apex was allowed to form a molecular layer on the aminosilylated surface through multipoint ionic attraction. It was found that a compact and smooth monolayer was obtained at appropriate condition. The film quality was maintained successfully after deprotecting CBZ group with trimethylsilyl iodide. The surface density of the primary amine after the deprotection was measured with fluorometry, and 0.1-0.2 amine group per 1 nm2 was observed. This implies that the spacing between the amine functional groups is 24-34 Å in hexagonal close packing (hcp) model. In addition, DNA microarrays were fabricated successfully on the dendron-modified surface.
We have studied ways to control density as well as spacing among functional groups. In particular, we observed that use of aziridine for the surface hyperbranching polymerization yielded extremely high surface density of primary amine that is useful for the immobilization of molecules of biological relevance such as oligo DNA. Also, an employment of dendrons of appropriate molecular architecture provided mesospacing among the reactive functional groups. The spacings was expected to guarantee the freedom of the biological macromolecules so that their properties are close to that in solution in spite of the confinement in the two dimensional world. We demonstrated that this was the case for oligonucleotide microarrays.