Chemically and geometrically defined poly (methyl methacrylate) (PMMA) substrates were employed to spatially immobilize biomolecules. First, we irradiated the PMMA substrate with 172 nm vacuum ultraviolet (VUV) light through a photomask to fabricate on its surface well-ordered arrays of micro/nanowells with a depth of 400 nm or less and an average diameter of 5, 10, or 20 mum. The surface of these wells was chemically reactive due to the formation of oxygen-containing functional groups during VUV irradiation, while the surrounding areas remained unreactive. We were therefore able by chemical vapor deposition to selectively and uniformly chemisorb aminosilane, that is, N-(6-aminohexyl)-3-aminopropyltrimethoxysilane (H2N[CH2](6)NHCH2CH2CH2Si[OCH3](3), AHAPS) onto the well surfaces without any marked change in the well's dimensions, as evidenced by x-ray photoelectron spectroscopy and atomic force microscope. Finally, we characterized the micro/nanowell arrays' property to immobilize bovine serum albumin (BSA) by utilizing antigen-antibody reactions. BSA antibody conjugated with fluorescein isothiocyanate was employed to visualize BSA adsorbed onto the microstructured sample surface coated with the AHAPS layer. We confirmed by fluorescence microscope that BSA indeed adsorbed onto the surfaces of the individual wells and did not adsorb onto the unirradiated regions between the wells. (C) 2004 American Vacuum Society.