Masami Kageshima

Noncontact atomic force microscopy in liquid environment with quartz tuning fork and carbon nanotube probe

A force sensor for noncontact atomic force microscopy in liquid environment was developed by combining a multiwalled carbon nanotube (MWNT) probe with a quartz tuning fork. Solvation shells of octamethylcyclotetrasiloxane on a graphite surface were detected both in the frequency shift and dissipation. Due to the high aspect ratio of the CNT probe, the long-range background force was barely detectable in the solvation region.

Insight into conformational changes of a single α-helix peptide molecule through stiffness measurements

Stiffness variations during the conformational change of a single α-helix polylysine peptide molecule were measured in a liquid environment using atomic force microscopy (AFM) with magnetic cantilever modulation. At the initial stage of the stretching process the stiffness decreased due to the breaking of hydrogen bonds and then increased due to the stretching of the helix backbone. These changes were reversible on reversal of the stretching motion. Below pK, the stiffness did not show increase on reversal, indicating that the reforming of hydrogen bonds did not take place. Conformational changes in the molecule were examined via these changes in stiffness.

Lateral forces during manipulation of a single C60 molecule on the Si(001)-2×1 surface

Abstract A method to measure lateral manipulation forces of a single molecule or a cluster was developed by combining scanning tunneling microscopy with a special lateral force sensor. The tunneling current and lateral force associated with manipulation of a single C 60 molecule on the Si(0xa00xa01)-2×1 surface were measured simultaneously during raster scanning of the probe. From the measured lateral force profiles the molecular hopping motion was analyzed and an estimate of the elastic energy stored in the molecule was determined.

Scanning Tunneling Microscopy Study on c(6×2) Structure of Ag/Si(001)

The c(6×2) phase of a silver monolayer on Si(001) substrate was investigated by scanning tunneling microscopy (STM). The c(6×2) structure appeared when silver was deposited at room temperature and then annealed at temperatures between 100°C and 250°C, and always coexisted with a 2×3 structure. In contrast, when silver was deposited onto a substrate at a temperature in this range, only the 2×3 structure grew. In the STM images with negative and positive sample bias voltages, one and two maxima were observed, respectively, in a c(6×2) unit cell. The finding of a lack of mirror symmetry in the unit cell reveals that the previously reported single-domain c(6×2) surface actually consists of two crystalographically equivalent domains on a single-domain substrate.

Unfolding process of a single peptide molecule on a substrate was investigated by atomic force microscope

The unfolding process of a peptide on a gold substrate on the scale of a single molecule was investigated by measuring force curves using an atomic force microscope (AFM). The sequence of the synthesized peptide was AAKA (AEAAKA) 5 A-cysteine that formed an alpha-helix in a buffer. A single peptide molecule was stretched between the AFM tip and the substrate during the force curve measurement. In the force curves, many abrupt changes or jumps in cantilever deflection were observed during the peptide stretching. It seems likely that these discontinuities were due to the breaking of some hydrogen bonds of an alpha-helix as helical parts of the peptide were elongated to a stretched form. The distribution of lengths of the peptide elongation, as calculated from the discontinuity spacing, had two peaks around 8-11 and 18-21 A. This suggests that 1.5 or 3 turns of the helical parts of the peptide were ruptured simultaneously.

Investigation of Enzyme Activities of the Enzyme Immobilized on an AFM Tip

Enzyme activities of V8 protease on AFM tip were investigated by measuring its force curves. The enzyme was immobilized onto the surface of the chemically modified AFM tip; two kinds of peptides were immobilized to the mica surface by a hetero‐reactive reagent. One peptide was designed to be recognized and digested by the enzyme. Another was designed so as not to be recognized by the enzyme. Force curves were obtained by plotting the applied force on the cantilever as a function of the sample displacement. Force applied on the cantilever, over 1.5 nN, was often observed when the tip contacted to a peptide that was digestible by the enzyme. In contrast a force of less than 0.4 nN was observed for contact with other peptides. Large force over 1.5 nN seemed to be caused by rupturing of the intermediate form of the enzyme and the peptide. It was suggested that enzyme molecules on the AFM tip can recognize the target sequence of the peptide. This method can be a tool to analyze biomolecules on a surface.

Development of a Gene Transfer Technique Using AFM

We report on a new low invasive technique for gene transfer of living cells using an ultra thin needle, termed a nano‐needle, comprising part of an etched atomic force microscope (AFM) tip. A silicon AFM tip was sharpened using focused ion beam etching to create an etched Si tip with a small diameter (100 to 200 nm). This small diameter ensured no damage was caused to the cell during needle insertion. In this study, we have demonstrated the cell penetration process using a nano‐needle and a DNA immobilized nano‐needle. This new technique could be applied for control of gene expression in a single cell.