Ichiro Yamashita

Compositional Changes Induced by Ion Bombardment in Ferritin nanoparticles

A monolayer of inorganic nanoparticles was fabricated on a silicon wafer using a cage-shaped protein, ferritin, which can sequester several types of inorganic nanoparticles in their cavities. Ferritins were bound electrostatically in an aqueous condition to the silicon wafer, which was modified with aminosilane molecules. We have used X-ray photoelectron spectroscopy (XPS) to study the effects of ion bombardment on a freshly cleaned ferritin surface. Compositional changes induced by 3.0 keV Ar+ sputtering in Fe2O3-ferritin nanoparticles have been quantitatively studied by XPS. All the Fe2O3-ferritin nanoparticles showed important changes to Fe nanoparticles in their stoichiometry for 60 sec with Ar+ sputtering. Furthermore, Kelvin force microscopy (KFM) has shown that there exists a very high surface potential, probably owing to the reduction of the surface to its element induced by Ar+ ion bombardment. With regard to the origin of the surface reduction activities, the induced surface potential is discussed.

Fabrication of Nanodevices Using Nanoparticles Synthesized in Cage-Shaped Proteins

Fabrication of nanostructures by biomolecules, termed the “bio nano process (BNP),” has been proposed, and the process utilizes the biotemplated biomineralization of inorganic materials and self-assembly. NP synthesis by genetically modified cage-shaped proteins, ferritin, and DNA-binding protein from starved cells, Dps, is the most basic part of the BNP. The BNP can produce homogenous NPs inside cage-shaped protein. NP growth is limited by the protein shell and the same size NP can be produced. The surrounding protein shells deliver/array the accommodated NPs at designated positions through the interaction of the protein and inorganic material surface. Even a single NP placement to a nanodisk on a substrate is possible. In such placement and arraying, aptamer and electrostatic interactions play the important roles. Obtained NP arrays are proved to be able to fabricate key components of nanoelectronic devices through the integration of top-down and bottom-up technology. The BNP can also produce three-dimensional bioconjugate of cage-shaped proteins and CNTs. This new material has a quantum effect and high thermal insulation by the protein shell. The measurement of thermoelectric properties confirmed that this bioconjugate is a new type of thermoelectric materials.