Keita Mitsui

Mechanical unfolding of a2-macroglobulin molecules with atomic force microscope

α 2‐Macroglobutin was derivatized with a sulfhydryl cross‐linker and sandwiched between a mica substrate and a solicon nitride tip, both coated with gold, of an atomic force microscope and force curve measurement was carried out. An extensive downward deflection of the cantilever was observed in the retracting realm of the curve, when and only when the substrate was covered with the derivatized protein. The result was interpreted in terms of the mechanical stretching and unfolding of a single or a few protein molecules.

Mechanical measurements of a single protein molecule and human chromosomes by atomic force microscopy

Copyright (c) 1997 Elsevier Science S.A. All rights reserved. The force-distance mode of atomic force microscopy has been used to mechanically unfold sandwiched protein molecules between the tip and substrate. Under favorable conditions, average spring constants in the range of several tens of pN nm −1 were obtained for the stretching event of single protein molecules. Another series of force curves was recorded to perform indentation experiments on chromosomes, by pressing down an AFM tip beyond a soft chromosomal surface. The resulting force versus depth curves were analyzed to give estimates of the Youngs modulus of wet chromosomes in the range 0.5-1.1×10 5 N m −2 at neutral and alkaline pH, but it was 10 times higher in acetate buffer at pH 4.

Protein Stretching II*1: Results for Carbonic Anhydrase

The force curve measurement mode of an atomic force microscope was used to record the force required to stretch a protein molecule that was covalently sandwiched through gold-thiol bonds between a mica substrate and a silicon nitride tip, both coated with gold. In one experiment, 8 ± 1 out of 20 lysyl residues of bovine carbonic anhydrase B were randomly derivatized to give free thiols, and grafted on an atomically flat gold (111) surface on mica. Force curves taken on the surface covered with protein molecules using a gold coated tip occasionally showed a large downward deflection indicating trapping and subsequent stretching of protein molecules between the tip and the substrate. In another experiment, the same protein was genetically engineered so that cysteine residues were introduced at both the amino and the carboxyl terminus. Force curves taken in a similar manner as in the first experiment indicated almost complete extension of a linear polypeptide chain. The result was explained in terms of extension of a pseudo-three-dimensional get in both cases, with additional stretching of a linear chain in the second case.

Nanoscopic studies investigated by hybrid SNOM/STM

Abstract In order to improve the spatial resolution in scanning near-field optical microscopy (SNOM), we designed a hybrid system of illumination mode SNOM integrated with scanning tunnelling microscopy (STM) by introducing a metal-coated optical fiber tip with a nanometer-scale aperture. The aperture is also covered with a thin metal layer, thus the top of the aperture acts as an STM tip. We employed several materials to show the capability of our hybrid SNOM/STM system as a tool to investigate nanoscopic phenomena. We present a simultaneous SNOM/STM imaging of Au(111), where the SNOM image has a lateral resolution of the order of nanometers, quite comparable to that of the STM image. An azobenzene dye molecule embedded in liquid crystalline cyanobiphenyl molecules on MoS2 was also investigated.

Immobilization of DNA on Self-Assembled Monolayer

Abstract We attempted the immobilization of DNA onto self-assembled monolayer (SAM) which contains the intercalated for DNA. Anthryl moieties were attached to the terminal OH groups in SAM of 1-Mercapt-11-undecanol (MU-SAM) by esterification. In the case of the SAM containing anthryl moieties (Anth-SAM), surface plasmon resonance measurement indicates that the adsorption of DNA onto the SAM was observed in an aqueous DNA solution, and the DNA remained on the surface even after rinsing. Although the adsorption of DNA onto MU-SAM was also observed, little DNA remained on the SAM after rinsing. These results indicate that the anthracene which was attached to the SAM can interact with DNA because the binding ability was increased by introduction of anthracene moieties to the SAM.

Hybridization of scanning near-field optical microscope with scanning tunneling microscope

Abstract Scanning near-field optical microscope (SNOM) is hybridized with scanning tunneling microscope (STM) in order to achieve a higher spatial resolution by introducing a doubly metal-coated optical fiber tip with a nm-scale aperture. The result of a simultaneous SNOM/STM imaging of Au(111) indicates the boundary-sensitive detection in SNOM mode, which is not an artifact caused by z-motion crosstalk.

Development of a hybrid SNOM/STM and its application to organic ultra-thin films

Abstract In order to overcome one of the drawbacks in scanning near-field optical microscopy (SNOM), i.e., a low spatial resolution caused by a rather poor sample-probe distance control, we are designing a hybrid system of SNOM with scanning tunneling microscopy (STM) by introducing a metal-coated optical fiber tip with an apex of a nanometer-scale aperture. We present the recent developments of our homemade hybrid SNOM/STM system.

Adsorption Behavior of DNA onto Self-assembled Monolayer Containing Intercalator

Abstract We synthesized an unsymmetric disulfide containing an anthryl group, which can form a self-assembled monolayer (SAM) on a gold surface, to immobilize DNA onto the gold surface through the intercalation between DNA and anthryl groups. A surface plasmon resonance (SPR) measurement indicates that the SAM can detect DNA efficiently at a liquid-solid interface.