Yoichi Otsuka

We have studied the electrical conductivity of DNA film using nanogap electrodes. Current–voltage measurements and alternating current measurements were performed for analysis of conductivity. The electrical conductivity of the DNA films of poly(dG)·poly(dC) are found to depend strongly on the humidity. The resistance of poly(dG)·poly(dC) decreases dramatically with increasing relative humidity. The contact resistance between DNA film and Au electrodes is also examined by the conventional four-p

The method, named scanning probe electrospray ionization (SPESI), promises to be a simple and unique approach toward direct sampling and ionization methodology.

Conductance of bundled single-walled carbon nanotubes (b-SWCNTs) are measured by point-contact current-imaging atomic force microscopy (PCI–AFM). Simultaneous mapping of the topographic information and current through SWCNTs enable us to investigate the relationship between structure and conductance. Variation in resistance of a b-SWCNT indicates that the resistance between SWCNTs was higher than 107 Ω with strong voltage dependence. Because PCI–AFM measurement can obtain vertical conductance in

We have developed a fabrication method for nanogap electrodes without employing photo- or electron-beam lithography to measure the electrical characteristics of nanostructured molecules. This angle-controlled shadow-masking method enables us to construct nanogap electrodes without a wet process after the molecules are positioned on the substrate. The proposed method makes it possible to measure electrical characteristics without structurally deforming or denaturing the molecules due either to th

A new atomic force microscopy (AFM) technique, called point-contact current-imaging AFM (PCI-AFM)-which combines tapping mode (for mapping topographic image) and point-contact operation (for measuring current–voltage characteristics)-has been developed. This new AFM technique can simultaneously map high-resolution topographic image and measure spatially resolved I–V characteristics of materials (placed on an insulative substrate and connected to a gold electrode) on the nanoscale. The high perfo

Methods for ambient sampling and ionization enable chemical information to be obtained with minimal sample preparation. Also, imaging mass spectrometry (IMS) enables the spatial distribution of multiple components to be determined by a single measurement. Here, we report an improved method of tapping-mode scanning probe electrospray ionization (t-SPESI) for ambient sampling and ionization in which probe oscillation is stabilized by using a piezo actuator. We demonstrate negative-mode IMS of a mo

Direct extraction and ionization techniques using minute amounts of solvent can be employed for the rapid analysis of chemical components in a sample without any sample preparation steps. This type of approach is important for mass spectrometry imaging of samples with multiple chemical components that have different spatial distributions (i.e., biological tissues). To improve the spatial resolution of such imaging, it is necessary to reduce the solvent volume for extraction and deliver it to the

Mass spectrometry imaging is an informative approach for the comprehensive analysis of multiple components inside biological specimens. We used novel tapping-mode scanning probe electrospray ionization mass spectrometry method to visualize cancer-related chemical components in the mouse pancreas tissue section at a sampling pitch of 100 µm. Positive ion mode measurements from m/z 100 to 1500 resulted in the visualization of multiple components that are tentatively assigned as polyamines, lipids

We demonstrate multicolor, on-line visualization in label-free biomedical microscopy based on stimulated Raman scattering (SRS). Fast data acquisition of SRS spectral images and subsequent image generation are achieved. The loading vectors for the blind separation of chemical components are predetermined by multivariate analysis at a certain field of view (FOV) and are applied to execute on-line visualization of chemical images at other FOVs. We also show that the response time can be shortened

Mass spectrometry imaging (MSI) is an effective technique for visualizing the distribution of lipids in tissues. The direct extraction-ionization methods using minute volumes of solvent for local components have the advantage of rapid measurement without any sample pretreatment. For effective MSI of tissues, it is necessary to understand the effect of solvent physicochemical properties on ion images. In this study, we report solvent effects on the lipid imaging of mouse brain tissue by tapping-m

Conductive polymers are key building blocks for the construction of molecular devices, and it is crucial to elucidate the conduction properties in microscale-shaped nanometer-thickness thin films in which the number of conduction paths is limited. In this study, we describe the effect of chemical doping and spatial limitation on the electrical conduction properties of sulfonated polyaniline (SPAN) strips with nanometer thickness fabricated by fountain-pen lithography and consider their electrica

The development of analytical technology that allows investigation of the diversity of cells that form biological tissues based on molecular information is important to elucidate the heterogeneity of cells and pathological mechanisms. Here, we present a proof-of-concept demonstration of single-cell mass spectrometry imaging (SC-MSI) via tapping-mode scanning probe electrospray ionization (t-SPESI), which is an atmospheric-pressure sampling ionization technique. We developed a novel t-SPESI unit

A combination of direct liquid extraction using a small volume of solvent and electrospray ionization allows the rapid measurement of complex chemical components in biological samples and visualization of their distribution in tissue sections. This review describes the development of such techniques and their application to biological research since the first reports in the early 2000s. An overview of electrospray ionization, ion suppression in samples, and the acceleration of specific chemical

Mass spectrometry imaging (MSI) is a promising analytical method to visualize the distribution of lipids in biological tissues. To clarify the relationship between cellular distribution and lipid types in a tissue, it is crucial to achieve both an improvement in ion detection sensitivity and a reduction in the ionization area. We report methods for improving the efficiency of ion transfer to a mass spectrometer and miniaturizing the extraction area of a sample for tapping-mode scanning probe ele

Mass spectrometry imaging (MSI) is used for visualizing the distribution of components in solid samples, such as biological tissues, and requires a technique to ionize the components from local areas of the sample. Tapping-mode scanning probe electrospray ionization (t-SPESI) uses an oscillating capillary probe to extract components from a local area of a sample with a small volume of solvent and to perform electrospray ionization of those components at high speed. MSI can be conducted by scanni