Display of Amino Groups on Substrate Surfaces by Simple Dip-Coating of Methacrylate-Based Polymers and Its Application to DNA Immobilization

The implementation of a reactive functional group onto a material surface is of great importance. Reactive functional groups (e.g., an amino group and a hydroxyl group) are usually hydrophilic, which makes it difficult to display them on a dry polymer surface. We here propose a novel method for displaying amino groups on the surfaces of polymeric substrates through dip-coating of a methacrylate-based copolymer. We synthesized copolymers composed of methyl methacrylate and 2-aminoethyl methacrylate with different protecting groups or ion-complexes on their amino groups, then dip-coated the copolymers onto a poly­(methyl methacrylate) (PMMA) substrate. Evaluation using a cleavable fluorescent compound, which was synthesized in the present study to quantify a small amount (pmol/cm²) of amino groups on a solid surface, revealed that the protection of amino groups affected their surface segregation in the copolymer coating. p-Toluenesulfonate ion-complex and tert-butoxycarbonyl (Boc) protection of amino groups were found to effectively display amino groups on the surface (more than 70 pmol/cm²). The density of amino groups displayed on a surface can be easily controlled by mixing the copolymer and PMMA before dip-coating. Dip-coating of the copolymer with Boc protection on various polymeric substrates also successfully displayed amino groups on their surfaces. Finally, we demonstrated that the amino groups displayed can be utilized for the immobilization of a DNA oligonucleotide on a substrate surface.