A functionalized nanomaterial, such as a nanoparticle, can include a polythioaminal functionalized surface. The polythioaminal linked to the surface of the nanomaterial can be bonded to a compound such as therapeutic and/or diagnostic materials. The thiol-based linkages can be used to bond the polythioaminal to both the nanomaterial and the therapeutic and/or diagnostic materials. Polythioaminals can be prepared via reactions of triazine and dithiols. Polythioaminals thus prepared can be further modified to provide linkages to the nanomaterial and other compounds such as medicinal compound, peptides, and dyes. Nanomaterials including such compounds linked thereto via the polythioaminal can be supplied for therapeutic and/or diagnostic purposes to biological target regions.