A single-step method for applying a coating to a polymeric substrate comprising: Exposing a photoreactive compound and a polymeric compound dissolved in an aqueous solvent to ultraviolet radiation in the presence of said polymeric substrate to obtain a covalently bound coating thereon comprising a reaction product of the photoreactive compound and the polymeric compound, wherein said photoreactive compound is an aromatic ketone selected from the group consisting of a benzophenone derivative, an acetophenone derivative, an anthraquinone derivative, a thioxanthone derivative, and a ketocoumarin derivative, preferably wherein said photoreactive compound is selected from the group consisting of 4-benzoyl benzylamine, 2-aminobenzophenone, 3-aminobenzophenone, 4-aminobenzophenone, 3,4-diaminobenzophenone, 4,4'-diaminobenzophenone, 2-benzoyl benzoic acid, 4-benzoyl benzoic acid, 2-aminoacetophenone, 2'-aminoacetophenone, 2-aminobenzophenone-2'-carboxylic acid, 4-hydroxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2-acetylbenzoic acid, 4-acetylbenzoic acid, 2-(3-benzoylphenyl)propionic acid, anthraquinone-2-carboxylic acid, 1-aminoanthraquinone, 1,4-diaminoanthraquinone, 2-amino-7-methyl-9H-thioxanthen-9-one, 2-carboxy-9H-thioxanthene-9-one, and 2-(3-sulfopropoxy)-9H-thioxanthene-9-one or an inorganic or organic salt thereof; and wherein said polymeric compound is selected from the group consisting of polyethylene glycol, poly(vinyl pyrrolidone), polyacrylic acid, polyacrylamide (PAAM), dextran, and a poly(oxazoline) compound as well as esters, amines, acids, succinimidyl-modified acids, maleimides, biotinylated esters, biotinylated amines, biotinylated acids, and biotinylated maleimides thereof. Exposing a photoreactive compound and a polymeric compound dissolved in an aqueous solvent to ultraviolet radiation in the presence of said polymeric substrate to obtain a covalently bound coating thereon comprising a reaction product of the photoreactive compound and the polymeric compound, wherein said photoreactive compound is an aromatic ketone selected from the group consisting of a benzophenone derivative, an acetophenone derivative, an anthraquinone derivative, a thioxanthone derivative, and a ketocoumarin derivative, preferably wherein said photoreactive compound is selected from the group consisting of 4-benzoyl benzylamine, 2-aminobenzophenone, 3-aminobenzophenone, 4-aminobenzophenone, 3,4-diaminobenzophenone, 4,4'-diaminobenzophenone, 2-benzoyl benzoic acid, 4-benzoyl benzoic acid, 2-aminoacetophenone, 2'-aminoacetophenone, 2-aminobenzophenone-2'-carboxylic acid, 4-hydroxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2-acetylbenzoic acid, 4-acetylbenzoic acid, 2-(3-benzoylphenyl)propionic acid, anthraquinone-2-carboxylic acid, 1-aminoanthraquinone, 1,4-diaminoanthraquinone, 2-amino-7-methyl-9H-thioxanthen-9-one, 2-carboxy-9H-thioxanthene-9-one, and 2-(3-sulfopropoxy)-9H-thioxanthene-9-one or an inorganic or organic salt thereof; and wherein said polymeric compound is selected from the group consisting of polyethylene glycol, poly(vinyl pyrrolidone), polyacrylic acid, polyacrylamide (PAAM), dextran, and a poly(oxazoline) compound as well as esters, amines, acids, succinimidyl-modified acids, maleimides, biotinylated esters, biotinylated amines, biotinylated acids, and biotinylated maleimides thereof.