Yuko Ueno

THz Chemical Imaging for Biological Applications

THz spectroscopy is advantageous in analytical chemistry because it can detect and identify intermolecular interactions in chemical compounds, such as hydrogen bonds and hydrations, and molecular networks. Recent advances in THz components, such as ultrashort pulsed lasers and photoconductive antennas, have improved the sensitivity of THz time-domain (TDS) spectroscopy and have made the THz chemical imaging possible. THz chemical imaging can reveal hydrogen bond distributions and will be a very powerful tool in biology, pharmacology, and life sciences. THz-TDS is also promising for the quantitative chemical analysis and detection of molecules and clusters in nanospace and ice.

Application of a cubic-like mesoporous silica film to a surface photovoltage gas sensing system

Abstract A self-ordered cubic-like mesoporous silica film has been successfully fabricated in a metal–insulator–semiconductor (=Au/SiO 2 (cubic-like meso)/Si 3 N 4 /SiO 2 /Si) device based on the surface photovoltage (SPV) system and applied to an NO gas sensor. The self-ordered cubic-like mesoporous silica film is synthesized by using as a template in spin coating a nonionic poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO 100 –PPO 65 –PEO 100 ) type triblock copolymer surfactant. The sensing characteristics of the self-ordered cubic-like mesoporous SPV system have been investigated by repeated exposure to 100 ppm NO gas and standard air, as well as observation of the alternating (photo) current, which resulted from the physical adsorption and chemical interactions between detected NO gas and the self-ordered cubic-like mesoporous film. In sensing NO gas, this cubic-like mesoporous SPV system exhibits a response nearly five times larger than that of a simple SPV sensor without mesoporous silica film. Even at room temperature, this mesoporous SPV system exhibits a recoverable response. These results can be explained by the characteristics of the cubic-like mesoporous silica film including large surface area and a bi-continuous mesopore structure. This kind of mesoporous film has a great potential for application to highly sensitive and responsive gas sensors.

Terahertz-wave generation from quasi-phase-matched GaP for 1.55μm pumping

We have realized a terahertz (THz)-wave source employing difference frequency generation (DFG) from a quasi-phase-matched GaP stack pumped at 1.55μm. We observed THz waves with enhanced power by quasi-phase matching (QPM) in the ⟨110⟩ direction of GaP with a ⟨111⟩ polarization direction for the incidence of two pump lights with the same propagation and polarization directions. We obtained THz-wave power proportional to the product of two pump-light powers due to DFG. We also confirmed that power peaks appeared at around 1 and 2.6THz reflecting the first- and the third-order QPM, respectively.

Chemical Mapping of Pharmaceutical Cocrystals Using Terahertz Spectroscopic Imaging

Terahertz (THz) spectroscopic imaging is a promising technique for distinguishing pharmaceuticals of similar molecular composition but differing crystal structures. Physicochemical properties, for instance bioavailability, are manipulated by altering a drugs crystal structure through methods such as cocrystallization. Cocrystals are molecular complexes having crystal structures different from those of their pure components. A technique for identifying the two-dimensional distribution of these alternate forms is required. Here we present the first demonstration of THz spectroscopic imaging of cocrystals. THz spectra of caffeine-oxalic acid cocrystal measured at low temperature exhibit sharp peaks, enabling us to visualize the cocrystal distribution in nonuniform tablets. The cocrystal distribution was clearly identified using THz spectroscopic data, and the cocrystal concentration was calculated with 0.3-1.3% w/w error from the known total concentration. From this result, THz spectroscopy allows quantitative chemical mapping of cocrystals and offers researchers and drug developers a new analytical tool.

On-chip graphene oxide aptasensor for multiple protein detection.

The versatility of an on-chip graphene oxide (GO) aptasensor was successfully confirmed by the detection of three different proteins, namely, thrombin (TB), prostate specific antigen (PSA), and hemagglutinin (HA), simply by changing the aptamers but with the sensor composition remaining the same. The results indicate that both DNA and RNA aptamers immobilized on the GO surface are sufficiently active to realize an on-chip aptasensor. Molecular selectivity and concentration dependence were investigated in relation to TB and PSA detection by using a dual, triple, and quintuple microchannel configuration. The multiple target detection of TB and PSA on a single chip was also demonstrated by using a 2×3 linear-array GO aptasensor. This work enables us to apply this sensor to the development of a multicomponent analysis system for a wide variety of targets by choosing appropriate aptamers.

Soft X-ray emission and absorption spectra in the C K region of sputtered amorphous carbon films

Abstract Soft X-ray emission and absorption spectra in the C K region of amorphous carbon films systematically deposited by RF, ion-beam, and ECR sputtering under various deposition conditions were measured using highly brilliant synchrotron radiation. A broad main peak and a high-energy shoulder were observed in the emission spectra, and a fine structure consisting of at least five peaks was observed in the absorption spectra. By analogy to the occupied/unoccupied C2p-DOS obtained by DV-Xα molecular orbital calculations of simple cluster models composed of sp 2 and sp 3 carbon atoms, we approximately explained the spectral features in the measured X-ray emission spectra by σ and π bonds and estimated the fine structures in the absorption spectra by the hybridized unoccupied molecular orbitals formed by the local-structures composed of sp 2 and sp 3 carbon atoms.

Protein recognition on a single graphene oxide surface fixed on a solid support

We study protein recognition on a graphene oxide (GO) surface using a single GO piece fixed on a solid support. The GO surface is modified by newly designed processes using pyrene as a linker to an sp2 domain in the GO, an aptamer for thrombin recognition, and a probe dye for fluorescence detection. In this system, the dye probe fluorescence, which was initially quenched by GO, is recovered when the aptamer recognizes the corresponding protein. We demonstrate the label-free and selective protein recognition for thrombin. The elementary processes of protein recognition are observed directly with a confocal laser scanning microscope and an atomic force microscope using an identical piece of GO. They indicate that proteins are recognized homogeneously on the modified GO surface. We also show that the recognition system can be installed and operated in microchannel devices.

High benzene selectivity of uniform sub-nanometre pores of self-ordered mesoporous silicate

The high benzene gas selectivity of mesoporous silicate (SBA-15) was observed in the sub-nanometre micropore condensation region. The benzene/toluene ratios of the adsorbed amount were >100 and >6 in ideal and pseudo-atmospheric environments, respectively.

Terahertz Spectroscopic Imaging of Polymorphic Forms in Pharmaceutical Crystals

A terahertz spectroscopic imaging system was fabricated for the detection of two-dimensional molecular distributions in pharmaceutical tablets based on absorption peaks of intermolecular or intramolecular hydrogen bonds in crystals. The terahertz imaging system consists of a terahertz time-domain spectrometer and a three-dimension translational stage. Using the system, we obtained frequency-dependent terahertz images of famotidine polymorphic forms A and B. An offset subtraction process is useful for detecting the distribution in an inhomogeneous tablet containing a mixture of the two forms. The terahertz imaging technique is a valuable tool for the analysis of polymorphic forms of crystal in inhomogeneous pharmaceutical tablets.

Effect of the calcination temperature of self-ordered mesoporous silicate on its adsorption characteristics for aromatic hydrocarbons

We have studied the changes in the adsorption characteristics of mesoporous silicate (SBA-15) for benzene and toluene that are caused by using different calcination temperatures (Tc = 773 to 1173 K) in the synthesis process. We found that SBA-15 calcined at 773 K shows an extremely high benzene selectivity, especially in the low pressure region, while SBA-15 treated at higher Tc shows lower selectivity. In order to analyze the benzene selective mechanism, we studied the structures of the SBA-15 series, including their meso- and microporosity in detail. We found that the BET surface area (SBET) and the peak position of the mesopore diameter (2Rp) decreased, the peak position of the micropore diameter (2rp) increased, and the 2rp distribution became broader with increasing Tc. Among above factors, we conclude that the size and the distribution of 2rp are the most important to achieve a high benzene selectivity.