Takehiko Tsukahara

NMR studies of structure and dynamics of liquid molecules confined in extended nanospaces.

We fabricated an NMR cell equipped with 10-100 nm scale spaces on a glass substrate (called extended nanospaces), and investigated molecular structure and dynamics of water confined in the extended nanospaces by (1)H NMR chemical shift (delta(H)) and (1)H and (2)H NMR spin-lattice relaxation rate ((1)H- and (2)H-1/T(1)), (1)H NMR spin-spin relaxation rate ((1)H-1/T(2)), and (1)H NMR rotating-frame spin-lattice relaxation rate ((1)H-1/T(1rho)) measurements of H(2)O and (2)H(2)O. The delta(H) and (1)H- and (2)H-1/T(1) results showed that size-confinement produces slower translational motions and higher proton mobility of water, but does not affect the hydrogen-bonding structure and rotational motions. Such unique phenomena appeared in the space size of 40 to 800 nm. However, the (1)H-1/T(1) value at 40 nm was still different from that in 4 nm porous nanomaterial, because translational and rotational motions were inhibited for H(2)O molecules in the nanomaterial. By examining temperature- and deuterium-dependence of the (1)H-1/T(1) values, the molecular translational motions of the confined water were found to be controlled by protonic diffusion invoking a proton hopping pathway between adjacent water rather than hydrodynamic translational diffusion. Furthermore, we clarified that proton exchange between adjacent water molecules in extended nanospaces could be enhanced by the chemical exchange of protons between water and SiOH groups on glass surfaces, ( identical with SiO(-)...H(+)...H(2)O) + H(2)O --> triple bond SiO(-) + (H(3)O(+) + H(2)O) --> triple bond SiO(-) + (H(2)O + H(3)O(+)), based on (1)H-1/T(2) measurements. An enhancement of proton exchange rate of water due to the reduction of space sizes was verified from the results of (1)H-1/T(1rho) values, and the rate of water in the 100 nm sized spaces is larger by a factor of more than ten from that of bulk water. Such size-confinement effects were distinctly observed for hydrogen-bond solvents with strong proton-donating ability, while they did not appear for aprotic and nonpolar solvent cases. Based on these NMR results, we suggested that an intermediate phase, in which protons migrate through a hydrogen-bonding network and the water molecules are loosely coupled within 50 nm from the surface, exists mainly in extended nanospaces. This model could be supported by a three-phase theory based on the weight average of three phases invoking the bulk, adsorbed, and intermediate phases.

Femto Liquid Chromatography with Attoliter Sample Separation in the Extended Nanospace Channel

A liquid chromatography system, comprising a separation column with a width and depth of a few hundred nanometers, was fabricated on a glass microchip (femto liquid chromatography, fLC). The size of this system was approximately 10(11) times smaller than that of a conventional LC system, the flow rate was subpicoliter/minute, and the injection volume was a few hundred attoliters. The fLC system did not require packing stationary phase and was capable of separating solutes with different molecular charges (fluorescein and sulforhodamine B) that could not be separated on a conventional LC column whose surface was covered with the same functional group as that of the column of the fLC system. The fLC system represented herein overcomes limitations of conventional chromatography separation, namely, heterogeneity of the stationary phases and eddy diffusion. Scale-down of the chromatography system brought advantages not only in reduction of sample volume but also in separation efficiency. The fLC system can analyze a very small amount of sample with high efficiency and will be useful in analyzing small samples, such as single cells and synaptic clefts. fLC greatly influences and benefits various fields such as life sciences, medicine, environmental science, and manufacturing by the improvement of separation technology.

Serial DNA immobilization in micro- and extended nanospace channels

That focused arrays, even with a small set of ligands, provide more data than single point experiments is well established in the DNA microarray research field, but microarray technology has yet to be transferred to fused silica microchips. Fused silica microchips have several attractive features such as stability to pressure, solvents, acids and bases, and can be fabricated with minute dimensions, making them good candidates for nanofluidic research. However, due to harsh bonding conditions, DNA ligands must be immobilized after fabrication, thus preventing standard microarray spotting techniques from being used. In this paper, we provide tools for serial DNA immobilization in fused silica microchips using UV. We report the synthesis of a new UV-linker which was used to covalently couple functional DNA oligos to the inside of channels in fused silica microchips. With some simple modifications to our mask aligner, we were able to transfer OHP mask patterns, which allows the creation of basically any pattern in the channels. The functionality of the oligos was measured through the binding of fluorophore-labeled complementary target oligos. We examined parameters influencing DNA immobilization, and carry-over between spots after consecutive immobilizations inside the same channel. We also report the first successful multiple immobilizations of functional DNA oligos inside single channels of extended nanospace depth (460 nm).

Electrochemical studies on liquid properties in extended nanospaces using mercury microelectrodes

We developed a novel nanofluidic chip equipped with mercury microelectrodes, which enables electrochemical measurements to be made in 10–100 nm scale spaces (called extended nanospaces), and evaluated the performances. The effects of both space sizes and concentrations on the conductance (G) values of KCl solutions in extended nanospaces (216–5000 nm) were examined using impedance spectrometry. We found that the experimental G values in the extended nanospaces decreased non‐linearly with decreasing KCl concentrations in the range of 10−2 to 10−7 M and could be explained by theoretical model taking account of surface charge density of on a glass surface. This was found to result from enhancement of proton concentrations of the confined solution owing to fast proton exchange between SiOH groups on surfaces and water. Moreover, the G values provided the specific resistance and capacitance of KCl solutions in the extended nanospaces. These results showed that the viscosity of KCl solutions increased by size‐confinement and that the viscosity of solution in 216 nm‐sized extended nanospaces became about 2.8 times as large as that of bulk solution. We concluded that the developed nanofluidic chip becomes a new experimental tool for demonstrating confinement‐induced nanospatial electrochemical properties of liquids.

Integrated fluidic systems on a nanometer scale and the study on behavior of liquids in small confinement.

Nanofluidic systems and the studies on the behavior of liquids confined in nanometer-sized space are reviewed. Miniaturized chemical systems having nanometer-sized structures are fabricated by using advanced nanofabrication techniques. The size-confinement effect is expected to be applied in well-controlled chemical and biochemical analysis. While electroosmosis and electrokinetic migration in small-sized channels have been investigated extensively, there have been few reports on pressure-driven flow systems having nanometer-sized structures, which are widely used in laboratory-scale and micrometer-sized systems. In this review, fundamental technologies that can be used in integrated chemical analysis systems having nanometer-sized structures are introduced. In addition to the technological investigations, important topics in the fundamental research on the properties of liquids confined in nanometer-sized space are also presented.

Nanometer-level high-accuracy molding using a photo-curable silicone elastomer by suppressing thermal shrinkage

Although the so-called “labs-on-a-chip” or micro total analysis systems (micro TAS) fields hold high promise for applications in many fields, conventional fabrication processes based on the semiconductor industry such as photolithography have limitations in terms of productivity. Silicone elastomers are widely used for micromodeling and offer biocompatibility and chemical stability, but they are generally thermosetting and undergo unacceptable levels of shape deformation during curing. In this study, a photocurable silicone elastomer that has recently become commercially available was examined, and its basic optical, mechanical, and other related characteristics, along with its shape transfer capabilities, particularly its nanostructure replication characteristics, were measured in comparison with those of a representative existing thermosetting silicone elastomer. As a result, the photo-cured elastomer was shown to be superior to existing heat-cured silicone elastomers, having mechanical strength approximately three times greater, and was shown to have the same optical transmittance, extending from the near-IR to the near-UV regions. In addition, it was shown that the elastomer is sensitive to light in a wide range of wavelengths, from 254 to 600 nm, with no large difference in its curing characteristics, indicating that curing can be performed under a variety of common forms of illumination. Most importantly, the photocured elastomer provided extremely high replication accuracy due to its thermal shrinkage of less than 0.02%, compared to 2.91% in the heat-cured elastomer.

NMR studies on effects of temperature, pressure, and fluorination on structures and dynamics of alcohols in liquid and supercritical states.

We measured 1H NMR chemical shifts (delta H) and 1H and 2H NMR spin-lattice relaxation times (1H- and 2H-T1) of methanol, ethanol, 2-propanol, 2,2,2-trifluoroethanol, and 1,1,1,3,3,3-hexafluoro-2-propanol in the temperature range from 298 to 673 K at reduced pressures ( Pr = P/ Pc) of 1.22 and 3.14. The delta H values showed that the degree (X HB) of hydrogen bonding decreased in the order of methanol > ethanol >2-propanol > H2O, and that the hydrogen bonding was much affected by fluorination, because of the intramolecular H-F interactions in supercritical (sc) states. Moreover, 1H- T 1 measurements revealed that the relaxation processes of OH groups in nonfluoroalcohols are controlled by dipole-dipole (DD) and spin-rotation (SR) mechanisms below and above the critical temperature (Tc), while the cross-correlation effects connected with intramolecular DD interactions between a carbon atom and an adjacent proton played an important role for hydrocarbon groups (CHn, n = 1-3) under sc conditions. This interpretation was also supported by two other results. The first is that the intramolecular H-F interactions strongly inhibit the internal rotation of CH and CH2 groups of sc fluoroalcohols, and the second is that the molecular reorientational correlation times (tauc(D)) obtained from 2H- T 1 values of deuterated hydrocarbon groups (CDn ) at temperatures above T c have significantly less temperature dependence than those of OD groups. Actually, the apparent activation energy (DeltaEa) for molecular reorientational motions in sc alcohols was smaller compared with liquid alcohols, being about 1 order of magnitude.

Shift of isoelectric point in extended nanospace investigated by streaming current measurement

Isoelectric points in extended nanochannels (580-2720 nm) fabricated on fused-silica substrates were measured using the streaming current method. The isoelectric point obtained in a 2720 nm channel was almost the same as the isoelectric point reported for the bulk (2.6-3.2). However, the isoelectric point in the extended nanochannel (580 nm) was decreased to less than 2.0. This result provides important information for the modeling of ion transport in extended nanospace.

Dielectric Constant of Liquids Confined in the Extended Nanospace Measured by a Streaming Potential Method

Understanding liquid structure and the electrical properties of liquids confined in extended nanospaces (10-1000 nm) is important for nanofluidics and nanochemistry. To understand these liquid properties requires determination of the dielectric constant of liquids confined in extended nanospaces. A novel dielectric constant measurement method has thus been developed for extended nanospaces using a streaming potential method. We focused on the nonsteady-state streaming potential in extended nanospaces and successfully measured the dielectric constant of liquids within them without the use of probe molecules. The dielectric constant of water was determined to be significantly reduced by about 3 times compared to that of the bulk. This result contributes key information toward further understanding of the chemistry and fluidics in extended nanospaces.

Direct measurements of the saturated vapor pressure of water confined in extended nanospaces using capillary evaporation phenomena

Direct measurements of the saturated vapor pressures of water confined in extended nanospaces (10–100 nm scale) were realized using capillary evaporation phenomena. These results verified that the saturated vapor pressure was reduced with decreasing space sizes and that Kelvins equation was applicable even in extended nanospaces.