Futoshi Iwata

Determination of performance on tunnel conduction through molecular wire using a conductive atomic force microscope

Performance of nonresonant tunnel conduction through a self-assembled monolayer of conjugated molecules fabricated on gold (111) was determined by virtue of nanometer-scale electrical probe measurement using a conductive atomic force microscope. Electrical measurements with nanometer spatial resolution enabled mapping of tunnel current as well as efficiency of tunnel conduction through molecular wire by analyzing length dependence on current. A series of conjugated molecules with different numbers of oligothiophene rings proved to possess a high tunnel-conduction efficiency.

Scanning ion conductance microscopy for imaging biological samples in liquid: a comparative study with atomic force microscopy and scanning electron microscopy.

The present study was designed to show the applicability of scanning ion conductance microscopy (SICM) for imaging different types of biological samples. For this purpose, we first applied SICM to image collagen fibrils and showed the usefulness of the approach-retract scanning (ARS)/hopping mode for such samples with steep slopes. Comparison of SICM images with those obtained by AFM revealed that the ARS/hopping SICM mode can probe the surface topography of collagen fibrils and chromosomes at nanoscale resolution under liquid conditions. In addition, we successfully imaged cultured HeLa cells, with 15 μm in height by ARS/hopping SICM mode. Because SICM can obtain non-contact (or force-free) images, delicate cellular projections were visualized on the surface of the fixed cell. SICM imaging of live HeLa cells further demonstrated its applicability to study the morphological dynamics associated with biological processes on the time scale of minutes under liquid conditions. We further applied SICM for imaging the luminal surface of the trachea and succeeded in visualizing the surface of both ciliated and non-ciliated cells. These SICM images were comparable with those obtained by scanning electron microscopy. Although the dynamic mode of AFM provides better resolution than the ARS/hopping mode of SICM in some samples, only the latter can obtain contact-free images of samples with steep slopes, rendering it an important tool for observing live cells as well as unfixed or fixed soft samples with complicated shapes. Taken together, we demonstrate that SICM imaging, especially using an ARS/hopping mode, is a useful technique with unique capabilities for imaging the three-dimensional topography of a range of biological samples under physiologically relevant aqueous conditions.

Nanometre-scale deposition of colloidal Au particles using electrophoresis in a nanopipette probe

We describe a novel technique of local electrophoretic deposition of colloidal particles using a scanning probe microscope with a nanopipette probe filled with a colloidal solution. The colloidal solution including nanometre-scale particles was put into the nanopipette probe. A thin metal wire was inserted into the nanopipette probe as an electrode for the electrophoretic deposition. With the probe edge nearly in contact with the conductive surface and with an electric potential applied between the electrode and the surface, the colloidal particles migrated toward the edge of the probe, causing them to be deposited on the surface. It was possible for nanometre-scale Au colloidal particles in an aqueous solution to be deposited on Si surfaces. The size of the Au dots could be modified by adjusting the deposition time and voltage. Dot array and line patterns were successfully plotted on the surface. This technique of local deposition should provide the possibility for fabricating nanostructures such as nanomachines and nanoelectronics.

Nanometer-scale metal plating using a scanning shear-force microscope with an electrolyte-filled micropipette probe

We describe a novel technique of local metal plating using a scanning probe microscope with a micropipette probe filled with an electrolyte solution. An electrode wire inside the electrolyte-filled micropipette and Si surfaces were employed as the anode and the cathode, respectively. Nanometer-scale Cu dots could be electrochemically deposited on the Si surfaces as the micropipette probe was nearly in contact with the surfaces with application of a dc voltage between the electrode wire and the surfaces. It was possible to control the size of the Cu dots by adjusting the deposition time and voltage. Dot arrays and line patterns were sequentially fabricated as the pipette probe scanned the surfaces while changing the probe-to-surface distance under shear-force control. This technique of local metal plating could allow the fabrication of nanostructures such as nanomachines and nanoelectronics.

Nanomanipulation of biological samples using a compact atomic force microscope under scanning electron microscope observation.

We introduce a compact nanomanipulator that can be operated inside the sample chamber of a scanning electron microscope (SEM) for biological sample manipulation. The design of the nanomanipulator is based on that of an atomic force microscope (AFM). A self-sensitive cantilever is used to realize the compact body and thus it is possible to put a pair of the standalone AFM units on the sample stage in the SEM chamber. Using this system, we accomplished nanodissection of biological samples as well as AFM imaging under SEM observation. We then fabricated the surface of a rat renal glomerulus by scan-scratching and succeeded in making a small hole on the wall of a blood capillary. As a result, it was possible to observe the internal structure of the capillary, which had been hidden beneath the surface wall. Furthermore, using two AFM units on the sample stage of the SEM, we successfully dissected the lens fiber cells taken from a rat eye in a multi-probe operation using the two cantilevers. This system is expected to become a very useful tool for micro- and nanometer-scale anatomy and engineering applications.

Nanometer-scale layer modification of polycarbonate surface by scratching with tip oscillation using an atomic force microscope

This paper presents a simple and reliable technique for nanometer-scale layer modification of a polycarbonate (PC) surface using an atomic force microscope (AFM). The AFM tip, coated with amorphous carbon was made to oscillate vertically at its resonance frequency. With tip oscillating in tapping mode, it scan-scratched the PC surface to make the desired modification. This action carved the PC surface without distorting it. The bottom of the depression made by scan-scratching with the oscillating tip was obviously flat in comparison with the area scan-scratched without tip oscillation in contact mode. The depth of the scan-scratched depression was controlled by adjusting the amplitude of oscillation and the scanning speed of scratching. This technique is very interesting for microtribology and surface modification.

Oscillating high-aspect-ratio monolithic silicon nanoneedle array enables efficient delivery of functional bio-macromolecules into living cells

Delivery of biomolecules with use of nanostructures has been previously reported. However, both efficient and high-throughput intracellular delivery has proved difficult to achieve. Here, we report a novel material and device for the delivery of biomacromolecules into live cells. We attribute the successful results to the unique features of the system, which include high-aspect-ratio, uniform nanoneedles laid across a 2D array, combined with an oscillatory feature, which together allow rapid, forcible and efficient insertion and protein release into thousands of cells simultaneously.

Nanometer-Scale Manipulation and Ultrasonic Cutting Using an Atomic Force Microscope Controlled by a Haptic Device as a Human Interface

We describe a nanometer-scale manipulation and cutting method using ultrasonic oscillation scratching. The system is based on a modified atomic force microscope (AFM) coupled with a haptic device as a human interface. By handling the haptic device, the operator can directly move the AFM probe to manipulate nanometer scale objects and cut a surface while feeling the reaction from the surface in his or her fingers. As for manipulation using the system, nanometer-scale spheres were controllably moved by feeling the sensation of the AFM probe touching the spheres. As for cutting performance, the samples were prepared on an AT-cut quartz crystal resonator (QCR) set on an AFM sample holder. The QCR oscillates at its resonance frequency (9 MHz) with an amplitude of a few nanometers. Thus it is possible to cut the sample surface smoothly by the interaction between the AFM probe and the oscillating surface, even when the samples are viscoelastics such as polymers and biological samples. The ultrasonic nano-manipulation and cutting system would be a very useful and effective tool in the fields of nanometer-scale engineering and biological sciences.

Local elasticity imaging of nano bundle structure of polycarbonate surface using atomic force microscopy

The elasticity of the periodic bundle structure formed by the interaction between the tip of an atomic force microscope and a polycarbonate surface was studied. The local elasticity of the bundle was observed using ultrasonic force microscopy, which combines the sensitivity to an elastic structure of acoustic microscopy with atomic force microscopy. The mean height of the bundle increases with increase in the number of scan-scratching cycles. The process of decreasing elasticity of a growing bundle of polycarbonate was observed clearly. Furthermore, the elasticity contrast inside the bundle structure was observed by adjusting the amplitude of ultrasonic vibration of sample height in ultrasonic force microscopy.

Operation of Self-Sensitive Cantilever in Liquid for Multiprobe Manipulation

We describe a novel and simple operation method of using a self-sensitive cantilever of an atomic force microscopy (AFM) system in liquid. As for operation of the cantilever in liquid, Al lines of an integrated piezoresistor patterned on the cantilever are easily damaged by electrochemical corrosion. To realize safe operation without the damage, an additional electrode was inserted into the liquid. By applying DC voltage and controlling the potential of the electrode, the Al lines of the piezoresistor circuit on the cantilever could be protected from the electrochemical corrosion. By using this method, AFM imaging of collagen fibrils was demonstrated in physiological saline. Furthermore, the technique allowed us to realize a multiprobe AFM system with a simple configuration. Two cantilever probes were successfully operated like a knife and fork for the manipulation of collagen fibers in liquid.