We electrostatically placed a single ferritin molecule on a nanometric 3-aminopropyltriethoxysilane (APTES) pattern that was on an oxidized Si substrate. The numerical analysis of the total interaction free energy for ferritin predicted that a quadrilateral array of 15nm diameter APTES nanodisks placed at intervals of 100nm would accommodate a single molecule of ferritin in each disk under a Debye length of 14nm. The experiments we conducted conformed to theoretical predictions and we successfully placed a single ferritin molecule on each ATPES disk without ferritin adsorbing on the SiO2 substrate surface.
High-density cage-shaped proteins with inorganic cores were selectively adsorbed as a monolayer onto a 3-aminopropyltriethoxysilane (APTES) layer on a Si substrate. The electrostatic interaction between the protein and substrate surface was studied and it was proven that protein adsorption density depends on the quantitative balance of surface charge on the substrate and protein. The combination of a highly positive APTES layer and moderately negative ferritin, Fer-4, achieved an adsorption density of 7:6 Â 10 11 cm À2 and the combination of the APTES layer and Listeria ferritin (Lis-fer) reached an adsorption density of 1:3 Â 10 12 cm À2 . The adsorption process including the reduced charge of Lis-fer due to denaturation further enhanced the adsorption density up to 1:5 Â 10 12 cm À2 , whereas no Lis-fer was adsorbed onto the SiO 2 surface under the same conditions. This new technique makes it possible to produce a nanodot monolayer with a density higher than 1 Â 10 12 cm À2 , which can be applied to floating nanodot gate memories.
A two-dimensional hexagonally close-packed (2D-HCP) array of ferritin molecules with a nanoparticle core was fabricated directly on a carbonaceous solid substrate by genetically modifying the outer surface of the ferritin with carbonaceous materials-specific binding peptides. The displayed peptides endowed ferritins with a specific protein-substrate interaction and masked the strong nonspecific interaction. The specific interaction was weak enough to allow ferritins to be rearranged as well as an attractive protein-protein interaction that could be adjusted by selecting the buffer conditions. This method not only produced 2D-HCP arrays of ferritin but also 2D-ordered arrays of independent inorganic nanoparticles after protein elimination that can be applied to floating gate memories.
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