Biomedical subjects

Sho Kataoka

Publications and source records attributed to Sho Kataoka.

6 recordsLinked to original sources

PubMed2006

Probing molecular structure at interfaces for comparison with bulk solution behavior: water/2-propanol mixtures monitored by vibrational sum frequency spectroscopy.

The orientation of the isopropyl group at the liquid/vapor interface in 2-propanol/water binary mixtures was studied by vibrational sum frequency spectroscopy. The CH(3) stretch modes of the two methyl groups were used to determine the molecule's orientation by employing a novel united atom approach to model the (CH(3))(2)X moiety. For this purpose, the changes in the molecular susceptibility of the isopropyl group stretches were derived in the laboratory frame as a function of the tilt and twist angles. The results indicated that the methyl groups lay down on the surface at low alcohol mole fraction and gradually twisted with increasing mole fraction. At the azeotrope, x(iso) = 0.68, one of the methyl groups aligned approximately parallel to the surface normal, whereas the other was nearly parallel with the liquid/vapor interface. When the mole fraction of 2-propanol was higher than 0.68, the orientation of 2-propanol remained almost constant. The change in the alcohol's orientation with 2-propanol mole fraction closely tracked changes in its bulk activity coefficient. Such results lead to a picture in which the surface structure and bulk properties of the system are closely linked.

Journal Article↗

PubMed2006

Direct writing of metal nanoparticle films inside sealed microfluidic channels.

Herein we demonstrate the ability to pattern Ag nanoparticle films of arbitrary geometry inside sealed PDMS/TiO2/glass microfluidic devices. The technique can be employed with aqueous solutions at room temperature under mild conditions. A 6 nm TiO2 film is first deposited onto a planar Pyrex or silica substrate, which is subsequently bonded to a PDMS mold. UV light is then exposed through the device to reduce Ag+ from an aqueous solution to create a monolayer-thick film of Ag nanoparticles. We demonstrate that this on-chip deposition method can be exploited in a parallel fashion to synthesize nanoparticles of varying size by independently controlling the solution conditions in each microchannel in which the film is formed. The film morphology was checked by atomic force microscopy, and the results showed that the size of the nanoparticles was sensitive to solution pH. Additionally, we illustrate the ability to biofunctionalize these films with ligands for protein capture. The results indicated that this could be done with good discrimination between addressed locations and background. The technique appears to be quite general, and films of Pd, Cu, and Au could also be patterned.

Coated Materials, Biocompatible↗

PubMed2005

Effect of average phospholipid curvature on supported bilayer formation on glass by vesicle fusion.

The adsorption of large unilamellar vesicles composed of various combinations of phosphatidylcholine, phosphatidylethanolamine (PE), monomethyl PE, and dimethyl PE (PE-Me2) onto a glass surface was studied using fluorescence microscopy. The average lipid geometry within the vesicles, described mathematically by the average intrinsic curvature, C(0,ave), was methodically altered by changing the lipid ratios to determine the effect of intrinsic curvature on the ability of vesicles to rupture and form a supported lipid bilayer. We show that the ability of vesicles to create fluid planar bilayers is dependent on C(0,ave) and independent of the identity of the component lipids. When the C(0,ave) was approximately -0.1 nm(-1), the vesicles readily formed supported lipid bilayers with almost full mobility. In contrast, when the C(0,ave) ranged from approximately -0.2 to approximately -0.3 nm(-1), the adsorbed vesicles remained intact upon the surface. The results indicate that the average shape of lipid molecules within a vesicle (C(0,ave)) is essential for determining kinetically viable reactions that are responsible for global geometric changes.

Absorption↗

PubMed2005

Fluid and air-stable lipopolymer membranes for biosensor applications.

The behavior of poly(ethylene glycol) (PEG) conjugated lipids was investigated in planar supported egg phosphatidylcholine bilayers as a function of lipopolymer density, chain length of the PEG moiety, and type of alkyl chains on the PEG lipid. Fluorescence recovery after photobleaching measurements verified that dye-labeled lipids in the membrane as well as the lipopolymer itself maintained a substantial degree of fluidity under most conditions that were investigated. PEG densities exceeding the onset of the mushroom-to-brush phase transition were found to confer air stability to the supported membrane. On the other hand, substantial damage or complete delamination of the lipid bilayer was observed at lower polymer densities. The presence of PEG in the membrane did not substantially hinder the binding of streptavidin to biotinylated lipids present in the bilayer. Furthermore, above the onset of the transition into the brush phase, the protein binding properties of these membranes were found to be very resilient upon removal of the system from water, rigorous drying, and rehydration. These results indicate that supported phospholipid bilayers containing lipopolymers show promise as rugged sensor platforms for ligand-receptor binding.

Biosensing Techniques↗

PubMed2004

On the mechanism of the hofmeister effect.

Vibrational sum frequency spectroscopy was used to probe fatty amine monolayers spread on various electrolyte solutions. The spectra revealed ion specific changes in both monolayer ordering and water structure with the former following the Hofmeister series. Separate measurements of the surface potential as a function of ion tracked closely to changes in alkyl chain structure, but less closely to changes in water structure. The disruption of the monolayer ordering could be ascribed to the relative ability of the ions to penetrate past the hydrophilic surface of the monolayer's headgroups and into the more hydrophobic portion of the thin film. The corresponding trends observed in the surface water structure showed significant deviations from the Hofmeister series, leading to the conclusion that the changes in surface water structure, often credited with being the origin of Hofmeister effects, are probably not of primary importance. On the other hand, dispersion forces almost certainly play a large role in the order of the Hofmeister series.

Amines↗

PubMed2003

Thermodynamics of phase transitions in langmuir monolayers observed by vibrational sum frequency spectroscopy.

Vibrational sum-frequency spectroscopy (VSFS) was used to study gauche defects in octadecylamine (ODA) monolayers at the air/water interface. The VSFS spectra provide unique insights into phase transitions that occur as a result of changes in the structure of the monolayer's hydrophobic region. These changes can be attributed to the increased presence of gauche conformers in the ODA alkyl chains during the monolayer's transition from the solid to liquid phase. Temperature-dependent spectra from monolayers at several different pressures were used to assign the phase transition temperature based on the observed changes in microscopic structure. Through application of a two-dimensional form of the Clapeyron equation, the first in situ measurements of the entropy and enthalpy changes associated with gauche conformers in a monolayer were made.

Journal Article↗