Biomedical subjects

Haeng-Boo Kim

Publications and source records attributed to Haeng-Boo Kim.

9 recordsLinked to original sources

PubMed2006

Pressure-driven flow control system for nanofluidic chemical process.

We developed a novel flow control system for a nanofluidic chemical process. Generally, flow control in nanochannels is difficult because of its high-pressure loss with very small volume flow rate. In our flow control method, liquid pressure in a microchannel connected to the nanochannels is regulated by utilizing a backpressure regulator. The flow control method was verified by using simple structured microchip, which included parallel nanochannels. We found that the observed flow rate was three times lower than the value expected from Hagen-Poiseuille's equation. That implied a size-dependent viscosity change in the nanochannels. Then, we demonstrated mixing of two different fluorescent solutions in a Y-shaped nanochannel and also a proton exchange reaction in the Y-shaped nanochannel. The flow control method will contribute to further integration of nanochemical systems.

Microfluidics↗

PubMed2006

AC electroosmotic micromixer for chemical processing in a microchannel.

A rapid micromixer of fluids in a microchannel is presented. The mixer uses AC electroosmotic flow, which is induced by applying an AC voltage to a pair of coplanar meandering electrodes configured in parallel to the channel. To demonstrate performance of the mixer, dilution experiments were conducted using a dye solution in a channel of 120 microm width. Rapid mixing was observed for flow velocity up to 12 mm s(-1). The mixing time was 0.18 s, which was 20-fold faster than that of diffusional mixing without an additional mixing mechanism. Compared with the performance of reported micromixers, the present mixer worked with a shorter mixing length, particularly at low Peclet numbers (Pe < 2 x 10(3)).

Diffusion↗

PubMed2006

Liquid filling method for nanofluidic channels utilizing the high solubility of CO2.

We developed a fabrication method and a liquid filling method for a nano chemical reactor that used Y-shaped nanochannels specially designed for mixing and reacting. In order to reduce the pressure loss and to utilize the characteristics of the nanochannel, inlet microchannels were fabricated just beside the nanochannels. We investigated an initial liquid filling method into the nanochannels that ensured there were no air bubbles that could cause a flow stack due to the capillary pressure. In our method, the micro- and nanochannels were filled with carbon dioxide and any remaining air during the initial liquid introduction was dissolved utilizing the high solubility of carbon dioxide. We propose that chemical reactions in nanospaces can be realized by utilizing these fabrication and liquid introduction techniques.

Journal Article↗

PubMed2003

Characteristic electrochemical responses of polymer microchannel-microelectrode chips.

Polymer microchannel chips (dimension of the channel, 20 microm (depth) x 100 microm (width)) integrated with dual microband electrodes were fabricated by an imprinting method, and their characteristic electrochemical responses were elucidated in detail. A silicon micromachined template fabricated by photolithography and dry etching techniques was used for imprinting. An aqueous solution of a ferrocene derivative was brought into the microchannel by pressure-driven flow, and the electrode responses were studied on the basis of voltammetry and chronoamperometry. A linear sweep voltammetry of 1-hydroxyethylferrocene (FeCp-OH) in water demonstrated that the electrode responses in the microchannel chip were best characterized by one-dimensional diffusion along the channel length, reflecting the structural dimension of the channel. In generation-collection mode experiments, furthermore, a collection efficiency as high as approximately 90% was attained in the microchannel owing to both restricted space and characteristics of solution flow in the channel. It was confirmed that diffusion and solution flow made molecular transport very efficient in the microchannel. The experimental results were also compared with those predicted by computer simulations.

Journal Article↗

PubMed2003

Channel shape effects on the solution-flow characteristics and the liquid/liquid extraction efficiency in polymer microchannel chips.

A polymer microchannel chip with a symmetrical or unsymmetrical zigzag-side-walled structure was fabricated by an imprinting method, and applied to study shape effects on solution flow characteristics as well as on the liquid/liquid extraction efficiency of an aluminium(III) chelate complex (Al-DHAB: DHAB = o,o'-dihydroxyazobenzene) in a microchannel chip. In an unsymmetrical zigzag-side-walled channel chip (us-channel), an oil/water interface was sinusoidal, while that in a symmetrical zigzag-side-walled channel chip (s-channel) was flat as long as the observation was made under an optical microscope. It was demonstrated that the efficiency of the water-to-oil (1-butanol) extraction of Al-DHAB in the microchannel was governed by the contact time between the two phases. As the most important results, furthermore, the extraction efficiency was higher in the us-channel, as compared with that in the s-channel, owing to the sinusoidal liquid/liquid interfacial structure and, therefore, to the high interfacial area between the two phases.

Journal Article↗

PubMed2002

Nanochannels on a fused-silica microchip and liquid properties investigation by time-resolved fluorescence measurements.

We have fabricated nanometer-sized channels, demonstrated a technique for the introduction of liquid into the channels, and carried out time-resolved fluorescence measurements of aqueous solutions. In this study, 330-nm- and 850-nm-sized channels were fabricated on fused-silica substrates by fast atom beam etching and hydrofluoric acid bonding methods. A liquid introduction method utilizing capillary action was demonstrated. The liquid introduction was observed under an optical microscope, and the liquid velocity during the introduction was analyzed by surface energy and macroscale hydrodynamics. The liquid velocity due to capillary action in the nanometer-sized channel seemed more than four times slower than the estimation. Then, aqueous solutions of rhodamine 6G (R6G), sulforhodamine 101 (SR101), and rhodamine B (RB) in the channels were measured by time-resolved fluorescence spectroscopy; spectra of the same solution in a 250-microm-sized channel were also measured as a reference for the macrospace. Although the fluorescence spectra in the 330-nm-, 850-nm- and 250-microm-sized channels agreed with one another, the fluorescent decays in the nanometer-sized channels were faster for R6G and SR101 and slower for RB than the respective decays in the 250-microm-sized channels. The results suggested the solutions had lower dielectric constants and higher viscosities in the nanometer-sized channels.

Journal Article↗

PubMed2002

Chemical responses of single yeast cells studied by fluorescence microspectroscopy under solution-flow conditions.

A microspectroscopy system combined with a fluid manifold was developed to manipulate and analyze "single" living cells. A sample buffer solution containing living cells was introduced into a flow cell set on a thermostated microscope stage and a few cells were allowed to attach to the bottom wall of the flow cell. With these living cells being attached to the wall, other floating cells were pumped out by flowing a buffer solution. These procedures made it possible to keep a few cells in the flow cell and to analyze single cells by fluorescence microspectroscopy. The technique was applied to study the time course of staining processes of single living yeast (Saccharomyces cerevisiae) cells by using two types of a fluorescent probe. The present methodology was shown to be of primary importance for obtaining biochemical/physiological information on single living cells and also for studying cell-to-cell variations in several characteristics.

Flow Cytometry↗

PubMed2002

Photochemical ion receptor based on a structurally distorted ruthenium(II) complex having a crown-ether moiety at the 3,3'-positions on the 2,2'-bipyridine ligand.

Ru(bpy)2(CE-bpy)2+ was prepared where bpy and CE-bpy were 2,2'-bipyridine and bpy having a crown-ether moiety at the 3,3'-positions, respectively. Although Ru(bpy)2(CE-bpy)2+ showed only very weak emission in acetonitrile, recognition of Na+, Li+, or K+ by the crown-ether moiety in CE-bpy resulted in increases in both the emission intensity and the lifetime of the complex, demonstrating that it acted as a photoreceptor. The results were discussed in terms of a steric hindrance between the 3,3'-substituents on CE-bpy and structural changes in both CE-bpy and the complex upon ion recognition, as studied by variable-temperature 1H-NMR and steady-state/dynamic emission spectroscopy of the complex.

Journal Article↗

PubMed2001

Chelate Formation around a Hexarhenium Cluster Core by the Diphosphane Ligand Ph(2)P(CH(2))(6)PPh(2) This work was supported in part by Grant-in-Aid for Scientific Research No. 10149102 (Priority Area of "Metal-Assembled Complexes") from the Ministry of Education, Science, Sports, and Culture of Japan. Z.-N.C. is grateful to JSPS for a postdoctoral fellowship. The authors are grateful to Prof. C. Schäffer (University of Copenhagen) for his help in revising the manuscript.

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Journal Article↗