Nanostructured substrates for high density protein arrays

Nearly defect-free arrays of several 10⁴ gold dots of 12 ± 3 nm in diameter inside 10 nm deep cavities were fabricated for immobilization of proteins. Extreme ultraviolet interference lithography (EUV-IL) at the XIL-beamline of the Swiss Light Source was used to produce 140 nm period arrays of 50 nm holes in a 40 nm thick PMMA layer on oxidized silicon wafers. The size of the openings was reduced by glancing angle deposition (GLAD) of metals such as chromium and silver. Reactive ion etching of the underlying substrate, followed by deposition of a few nanometers of gold, lift-off and thermal annealing resulted in perfectly ordered arrays of small gold nanoparticles with well-defined size distribution. The combination of passivation of the silica surface with polyethylene glycol (PEG) derivatives and functionalization of gold with thiols enables the preparation of large area arrays of well separated functional protein molecules.