Biomedical subjects

Nae Yoon Lee

Publications and source records attributed to Nae Yoon Lee.

7 recordsLinked to original sources

PubMed2006

Hydrophilic composite elastomeric mold for high-resolution soft lithography.

Here, we introduce a nanopatternable hydrophilic composite elastomer highly desirable for both nanostructure patterning via solvent-assisted micromolding (SAMIM) and microcontact printing of polar inks. This composite precursor is prepared by blending two UV-curable materials, Norland Optical Adhesives (NOA) 63 and poly(ethylene glycol) diacrylate (PEGDA), in an appropriate ratio; upon UV polymerization, a nanopatternable elastomer with preferential permeability both to aqueous and organic solvent is fabricated. Using this composite mold, nanoscale SAMIM of poly(4-vinylpyridine) (P4VP) and microcontact printing of a polar biomolecule, bovine serum albumin (BSA), was successfully demonstrated, paving the way for facile and efficient reproduction of various nanopatterns and a biomolecule-printed array platform.

Elastomers↗

PubMed2006

Multilayer transfer printing on microreservoir-patterned substrate employing hydrophilic composite mold for selective immobilization of biomolecules.

In this study, we introduce a hydrophilic composite mold with elasticity and moderate water permeability, suitable for transferring water-soluble polar molecules such as polyelectrolyte multilayer. This composite mold is constructed from two UV-curable polymers-Norland Optical Adhesives (NOA) 63, a urethane-related polymer, and poly(ethylene glycol) diacrylate (PEGDA). The mixture of inherently hard NOA 63 and hydrogel precursor, PEGDA, resulted in an optically transparent mold with some degree of elasticity and enhanced water permeability upon UV polymerization. Employing the NOA 63-PEGDA composite mold, a polyelectrolyte multilayer comprising alternate thin layers of poly(acrylic acid) (PAA) and poly(acrylamide) (PAAm) was transfer-printed onto arrays of microreservoir-patterned substrate to selectively prevent unwanted adsorption of biomolecules on the protruding surface. Antibody was immobilized selectively inside the microreservoirs where multilayer was not transferred, and a specific antibody binding reaction was detected inside the microreservoirs. Furthermore, the potential of this composite mold as a convenient tool for constructing a biosensor for detecting Escherichia coli (E. coli) O157:H7 was explored.

Antibodies↗

PubMed2006

Removal of hydrogen sulfide by sulfate-resistant Acidithiobacillus thiooxidans AZ11.

Toxic H2S gas is an important industrial pollutant that is applied to biofiltration. Here, we examined the effects of factors such as inlet concentration and space velocity on the removal efficiency of a bacterial strain capable of tolerating high sulfate concentrations and low pH conditions. We examined three strains of Acidithiobacillus thiooxidans known to have sulfur-oxidizing activity, and identified strain AZ11 as having the highest tolerance for sulfate. A. thiooxidans AZ11 could grow at pH 0.2 in the presence of 74 g l(-1) sulfate, the final oxidation product of elemental sulfur, in the culture broth. Under these conditions, the specific sulfur oxidation rate was 2.9 g-S g-DCW (dry cell weight)(-1) d(-1). The maximum specific sulfur oxidation rate of A. thiooxidans AZ11 was 21.2 g-S g-DCW(-1) d(-1), which was observed in the presence of 4.2 g-SO4(2-) l(-1) and pH 1.5, in the culture medium. To test the effects of various factors on biofiltration by this strain, A. thiooxidans AZ11 was inoculated into a porous ceramic biofilter. First, a maximum inlet loading of 670 g-S m(-3) h(-1) was applied with a constant space velocity (SV) of 200 h(-1) (residence time, 18 s) and the inlet concentration of H2S was experimentally increased from 200 ppmv to 2200 ppmv. Under these conditions, less than 0.1 ppmv H2S was detected at the biofilter outlet. When the inlet H2S was maintained at a constant concentration of 200 ppmv and the SV was increased from 200 h(-1) to 400 h(-1) (residence time, 9 s), an H2S removal of 99.9% was obtained. However, H2S removal efficiencies decreased to 98% and 94% when the SV was set to 500 h(-1) (residence time, 7.2 s) and 600 h(-1) (residence time, 6 s), respectively. The critical elimination capacity guaranteeing 96% removal of the inlet H2S was determined to be 160 g-S m(-3) h(-1) at a space velocity of 600 h(-1). Collectively, these findings show for the first time that a sulfur oxidizing bacterium has a high sulfate tolerance and a high sulfur oxidizing activity below pH 1.

Acidithiobacillus thiooxidans↗

PubMed2005

Selective patterning and immobilization of biomolecules within precisely-defined micro-reservoirs.

Herein, we present the fabrication of well-defined micro-reservoirs and a simple strategy to immobilize biomolecules selectively inside the reservoirs. The micro-reservoirs are fabricated using a photocurable prepolymer, which enables the formation of concrete structures with high-fidelity, so that the reservoirs are spatially-segregated from each other by rigid physical barriers. For the directed binding of the protein, two steps are involved. First, poly(ethylene glycol) (PEG) is contact-printed on those areas where the protein binding is not desired, and next, protein binding is promoted where desired via carbodiimide chemistry. Fluorescein-tagged albumin is successfully immobilized inside the micro-reservoirs and microchannel arrays with high sensitivity, regardless of the sizes of the reservoirs and channels. The proposed system can be used for constructing multi-functional biosensors by immobilizing individual bioorganisms specifically in each micro-reservoir or microchannel.

Albumins↗

PubMed2005

Development of a passive micromixer based on repeated fluid twisting and flattening, and its application to DNA purification.

We have developed a three-dimensional passive micromixer based on new mixing principles, fluid twisting and flattening. This micromixer is constructed by repeating two microchannel segments, a "main channel" and a "flattened channel", which are very different in size and are arranged perpendicularly. At the intersection of these segments the fluid inside the micromixer is twisted and then, in the flattened channel, the diffusion length is greatly reduced, achieving high mixing efficiency. Several types of micromixer were fabricated and the effect of microchannel geometry on mixing performance was evaluated. We also integrated this micromixer with a miniaturized DNA purification device, in which the concentration of the buffer solution could be rapidly changed, to perform DNA purification based on solid-phase extraction.

Chemical Fractionation↗

PubMed2005

Control-free air vent system for ultra-low volume sample injection on a microfabricated device.

An improved method of sample injection was demonstrated for introducing ultra-low volume liquid on a microfabricated device. In our previous study, a pressure-driven injection method has been introduced and was applied to on-chip electrophoresis. In this study, the need for control of the air vent, which was indispensable for sample injection in the previous study, was completely eliminated, facilitating sample injection with great simplicity and high accuracy. This was realized by altering the topology of the air vent channel, which is connected to a hydrophobic and narrow channel (called a passive valve). Several types of air vent channels were designed and their injection performances were tested. In addition, by modifying the shape and the position of air vent channel and passive valve, the residual liquid volume inside the passive valve after sample injection was decreased to approximately 0.5% of the injected volume, a value which showed high reproducibility.

Journal Article↗

PubMed2004

Pressure-driven sample injection with quantitative liquid dispensing for on-chip electrophoresis.

A novel pressure-driven sample injection method was developed as an alternative to electrokinetic injection, and electrophoretic separation was carried out on a microfabricated device employing this method. This method enables a defined volume of liquid dispensing, followed by instantaneous injection driven by pneumatic pressure, greatly simplifying the injection procedure. A particular microstructure, called a "metering chamber", has been designed for the quantitative dispensing of an ultra-low volume of sample liquid; a "hydrophobic passive valve" equipped with an air vent channel is employed for injecting a dispensed sample into the separation channel. The reproducibility of dispensing was 3.3% (n = 15), expressed by the variation of dispensed volumes. The electrophoretic separation of DNA fragments was performed using this injection method, varying the injection volumes from 0.45 to 4.0 nL, and the separation efficiencies were compared. This precise injection method, easily variable in injection volumes, is highly suitable for quantitative as well as qualitative electrophoretic analyses.

DNA↗