High-density and highly surface selective adsorption of protein-nanoparticle complexes by controlling electrostatic interaction

High-density cage-shaped proteins with inorganic cores were selectively adsorbed as a monolayer onto a 3-aminopropyl-triethoxysilane (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 x 10(11) cm(-2) and the combination of the APTES layer and Listeria ferritin (Lis-fer) reached an adsorption density of 1.3 x 10(12) cm(-2). The adsorption process including the reduced charge of Lis-fer due to denaturation further enhanced the adsorption density up to 1.5 x 10(12) mm(-2), whereas no Lis-fer was adsorbed onto the SiO2 surface under the same conditions. This new technique makes it possible to produce a nanodot monolayer with a density higher than 1 x 10(12) cm(-2), which can be applied to floating nanodot gate memories.