The ultra-thin polypeptoid brush monolayers are excellent surface modification materials because they can be used to controllably tune the surface properties of Si substrates. Using polypeptoids with a terminal hydroxyl group, we demonstrate that through designing monomer chemistry and composition, different level of complexity in modifying surface properties can be achieved: from the simplest surface energy, to affinity towards biomolecules from passivation to preferential attachment, and further to specific binding of biomolecules.