Kiyohito Yamada

Electrostatic placement of single ferritin molecules

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 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 7.6×1011 cm-2 and the combination of the APTES layer and Listeria ferritin (Lis-fer) reached an adsorption density of 1.3×1012 cm-2. The adsorption process including the reduced charge of Lis-fer due to denaturation further enhanced the adsorption density up to 1.5×1012 cm-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 1×1012 cm-2, which can be applied to floating nanodot gate memories.

Making Monolayer of Inorganic Nanoparticles on Silicon Substrate

A monolayer of inorganic nanoparticles (NPs) was fabricated on a silicon wafer using a cage-shaped protein, ferritin, which can sequester several kinds of inorganic NP in their cavities. Ferritins were bound electrostatically in aqueous condition to the silicon wafer which was modified with aminosilane molecules. The obtained sample was heat-treated at 500°C under oxygen gas, and the protein moiety and aminosilane were completely eliminated. The obtained NP monolayer showed no aggregation or sintering. This new method can be used to produce a dispersed inorganic NP monolayer on a silicon substrate as designed, which could be used as a nanodot array in floating nanodot gate memories.

Effects of Dot Density and Dot Size on Charge Injection Characteristics in Nanodot Array Produced by Protein Supramolecules

The charge injection characteristics of nanodot arrays for floating nanodot gate memories (FNGMs) were studied using a metal–oxide–semiconductor (MOS) capacitor having density-controlled arrays of homogenous nanodots in a SiO2 layer. Nanodot arrays were prepared using cage-shaped proteins, Listeria ferritin and ferritin with a nanodot core, the diameters of which are 4.5 and 7 nm, respectively. Dot densities are from 3.3×109 to 1.8×1012 cm-2 for Listeria ferritin and from 3.8×109 to 7.9×1011 cm-2 for ferritin. The capacitance–voltage (C–V) characteristics of the obtained MOS capacitors were measured at 1 MHz by applying a DC bias voltage from -10 to +10 V. The flat-band voltage shift was found to depend on both dot density and dot size, and to be numerically proportional to the sum of the upper hemisphere surface areas of nanodots. It is important to balance dot density and dot size in order to fabricate advanced FNGMs, and the appropriate design of the array is necessary.

Floating Gate Metal–Oxide–Semiconductor Capacitor Employing Array of High-Density Nanodots Produced by Protein Supramolecule

An array of high-density 1.8×1012 cm-2 floating nanodots was embedded within a metal–oxide–semiconductor (MOS) capacitor using a cage-shaped protein supramolecule, Listeria ferritin (Lis-fer). A monolayer of Lis-fer with a 4.5 nm ferrihydrite core was adsorbed on a 3 nm tunneling SiO2 layer on a p-Si substrate by 3-aminopropyl-triethoxysilane (APTES) surface modification. The outer protein was selectively removed and the obtained cores were covered with a 20-nm-thick control SiO2 layer and an aluminum electrode. The MOS capacitor was annealed in reducing gas (H2:N2=10:90%), and the embedded cores were reduced to conductive nanodots. The capacitance–voltage characteristics of the MOS capacitor measured at 1 MHz by applying a DC bias voltage from -5 to +5 V showed a clear hysteresis. This result indicates that the array of nanodots produced and positioned by Lis-fer has the ability for electron confinement.

Electrostatic Placement of Nanodots onto Silicon Substrate Using Ferritin Protein Supramolecules with Control of Electrostatic Interaction in Solution

The behavior of the electrostatic adsorption of a single ferritin protein supramolecule, which formed a nanodot in its inner cavity, on a nanometric 3-aminopropyltriethoxysilane (APTES) pattern made on an oxidized Si substrate was studied using a numerical calculation. The total interaction free energy of the system, which included a ferrin, a substrate with an APTES nanopattern and a buffer solution, was calculated. The obtained distribution of the interaction potential that ferritin experiences can be used to explain theoretically the ferritin adsorption onto a quadrilateral array of 15-nm-diameter APTES nanodisks placed at intervals of 100 nm under a Debye length of 14 nm. This numerical calculation method described here can be applied to the estimation of the electrostatic adsorption behavior of nanometer-sized material as well as proteins.

Adsorption Properties of a Gold-Binding Peptide Assessed by its Attachment to a Recombinant Apoferritin Molecule

The adsorption properties of a recombinant apoferritin protein fused to a gold-binding peptide were characterized. The results of quartz crystal microbalance measurements showed that the fusion protein preferentially adsorbs to gold surfaces. Scanning electron microscopy also revealed that the protein selectively adsorbed onto a nanometer-scale gold pattern on a SiO2 surface fabricated by electron-beam lithography. Our results indicate that nanodots and nanowires synthesized using a biotemplate can be selectively placed onto a gold surface by genetically modifying the outer surface of the biotemplate. This technique represents an important step toward biotemplate-mediated fabrication of a nanometer-scaled device that utilizes gold electrodes.

Floating Gate MOS Capacitor with High-Density Nanodots Array Produced by Protein Supramolecule

Produced by Protein Supramolecule Kiyohito Yamada , Shigeo Yoshii, Shinya Kumagai, Atsushi Miura, Yukiharu Uraoka, Takashi Fuyuki and Ichiro Yamashita 2, 3 Advanced Technology Research Laboratories, Matsushita Electric Industrial Co., Ltd., 3-4 Hikaridai, Seika, Kyoto 619-0237, Japan Phone: +81-774-98-2516 E-mail:yamashita.ichiro@jp.panasonic.com Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan