A substrate comprises a surface, and a plurality of moieties, on at least a portion of the surface. The moieties are moieties of formula: Surf-L-Q-T, where -T comprises a reactant ligand, and Surf- designates where the moiety attaches to the surface. The substrate can be made into a protein chip by the reaction of a reactant ligand and a fusion polypeptide, where the fusion polypeptide includes a capture polypeptide moiety which corresponds to the reactant ligand.