Single-crystalline nanogap electrodes: enhancing the nanowire-breakdown process with a gaseous environment.

A method for fabricating single-crystalline nanogaps on Si substrates was developed. Polycrystalline Pt nanowires on Si substrates were broken down by current flow under various gaseous environments. The crystal structure of the nanogap electrode was evaluated using scanning electron microscopy and transmission electron microscopy. Nanogap electrodes sandwiched between Pt-large-crystal-grains were obtained by the breakdown of the wire in an O(2) or H(2) atmosphere. These nanogap electrodes show intense spots in the electron diffraction pattern. The diffraction pattern corresponds to Pt (111), indicating that single-crystal grains are grown by the electrical wire breakdown process in an O(2) or H(2) atmosphere. The Pt wires that have (111)-texture and coherent boundaries can be considered ideal as interconnectors for single molecular electronics. The simple method for fabrication of a single-crystalline nanogap is one of the first steps toward standard nanogap electrodes for single molecular instruments and opens the door to future research on physical phenomena in nanospaces.

Controlled dispersion and purification of protein-carbon nanotube conjugates using guanidine hydrochloride.

For the development of biofunctional carbon nanotubes for biosensors, drug carriers, and nanobiocatalysts, their aggregation and biofouling in aqueous solutions are crucial problems because this behavior leads to a reduction of their excellent optical and electrical properties and nanoscale size effects. This paper presents a new method for enhancing the dispersibility of protein-carbon nanotube conjugates and for exfoliating the protein from the carbon nanotube sidewalls through controlling the concentration of guanidine hydrochloride (Gdn·HCl) in the solution. In medium concentrations (2-3 M) of Gdn·HCl, the dispersibility of protein-carbon nanotube conjugates was found to be substantially increased without denaturation or aggregation of the proteins. At higher concentrations (>6 M) of Gdn·HCl, pristine carbon nanotubes were precipitated instantly as a result of dissociation of the protein. These phenomena indicate that Gdn·HCl functions not only as a dispersion adjuvant for biofunctional protein-carbon nanotube conjugates, but also as a cleaning agent for the purification of biofouled carbon nanotubes. The dissociation concentrations of Gdn·HCl were higher than the midpoint of protein denaturation, suggesting that protein adsorption on carbon nanotubes is more stable than protein folding toward Gdn·HCl.