A method for coimmobilizing two or more biomolecules on a substrate in a defined ratio is disclosed. The method uses a copolymer conjugated to a number, N, of different types of oligonucleotides. The copolymer can be adsorbed to the surface of the substrate. N types of oligonucleotides complementary to the copolymer-bound oligonucleotides can be conjugated to N types of biomolecules. The types of the copolymer-bound oligonucleotides can be mixed in a defined ratio then adsorbed to the surface. The biomolecule-bound complementary oligonucletides can be conjugated to the copolymer-oligonucleotides to create a substrate with the biomolecules coimmobilized in a defined ratio. The invention also relates to a substrate prepared by the method of the invention.