Biomedical subjects

Jongyoon Han

Publications and source records attributed to Jongyoon Han.

5 recordsLinked to original sources

PubMed2005

Million-fold preconcentration of proteins and peptides by nanofluidic filter.

We have developed a highly efficient microfluidic sample preconcentration device based on the electrokinetic trapping mechanism enabled by nanofluidic filters. The device, fabricated by standard photolithography and etching techniques, generates an extended space charge region within a microchannel, which was used to both collect and trap the molecules efficiently. The electrokinetic trapping and collection can be maintained for several hours, and concentration factors as high as 10(6)-10(8) have been demonstrated. This device could be useful in various bioanalysis microsystems, due to its simplicity, performance, robustness, and integrabilty to other separation and detection systems.

Electrophoresis↗

PubMed2005

Fabrication and characterization of 20 nm planar nanofluidic channels by glass-glass and glass-silicon bonding.

We have characterized glass-glass and glass-Si bonding processes for the fabrication of wide, shallow nanofluidic channels with depths down to the nanometer scale. Nanochannels on glass or Si substrate are formed by reactive ion etching or a wet etching process, and are sealed with another flat substrate either by glass-glass fusion bonding (550 degrees C) or an anodic bonding process. We demonstrate that glass-glass nanofluidic channels as shallow as 25 nm with low aspect ratio of 0.0005 (depth to width) can be achieved with the developed glass-glass bonding technique. We also find that silicon-glass nanofluidic channels, as shallow as 20 nm with aspect ratio of 0.004, can be reliably obtained with the anodic bonding technique. The thickness uniformity of sealed nanofluidic channels is confirmed by cross-sectional SEM analysis after bonding. It is shown that there is no significant change in the depth of the nanofluidic channels due to anodic bonding and glass-glass fusion bonding processes.

Journal Article↗

PubMed2004

Rapid protein separations in ultra-short microchannels: microchip sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing.

We have developed novel protein gel electrophoresis techniques, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and isoelectric focusing (IEF) in short microchannels (approximately millimeters) that take less than a minute. A photopatterning technique was used to cast in situ crosslinked polyacrylamide gel in a microchannel to perform SDS-PAGE. A fluorescent protein marker sample (Mr range of 20,000-200,000) was separated in less than 30 s in less than 2 mm of channel length. Crosslinked polyacrylamide gel, patterned in channels using UV light, provides higher sieving power and sample stacking effect, therefore yielding faster and higher-resolution separation in a chip. IEF of proteins was also achieved in a microchannel, and several proteins were focussed within tens of seconds in mm-length channels. As resolution in IEF is independent of separation distance, focusing in ultra-short channels results in not only faster separation but also more concentrated bands potentially allowing detection of low-concentration species.

Electrophoresis, Polyacrylamide Gel↗

PubMed2004

Two-dimensional protein separation with advanced sample and buffer isolation using microfluidic valves.

Methods are described to achieve more efficient multidimensional protein separation in a microfluidic channel. The new methods couple isoelectric focusing (IEF) with high ionic strength electrophoretic separations by active microvalve control in a microchip. Several experiments demonstrating independent 2D separation were performed, and critical parameters for optimal chip performance were identified, including channel passivation, electroosmosis control, and IEF linearity control. This strategy can be used for integration of different heterogeneous separation techniques, such as IEF, capillary electrophoresis, and liquid chromatography. This new device can be ideal for preseparation and preconcentration of complex biomolecule samples for a streamlined biomolecule analysis using mass spectrometry.

Buffers↗

PubMed2002

Characterization and optimization of an entropic trap for DNA separation.

Recently, a microfabricated entropic trap array was demonstrated to be useful in separating large (5-200 kbp) DNA molecules efficiently (within approximately 30 min), by dc electrophoresis, on a microchip platform without a sieving matrix. This paper reports further development of the technique, with emphasis on optimizing separation selectivity and resolution. The interaction of DNA molecules with regularly spaced entropic barriers was modeled in order to predict the effect of changing various structural parameters. The selectivity (differential mobility) was shown to be dependent on the depth of deep and shallow channel regions, applied electric field, and number of entropic barriers. Experimental data were compared with the prediction of the model. It was expected from the model that, in the low-field (severe trapping) limit, separation resolution should depend only on the number of entropic traps. However, in reality, resolution did depend on the applied field because the relaxation of DNA is not achieved at high fields. The requirement and feasibility of megabase pair DNA separation with the entropic trap array device was discussed.

DNA↗