Kyung Won Ro

Poly(dimethylsiloxane) microchip for precolumn reaction and micellar electrokinetic chromatography of biogenic amines

We have demonstrated that precolumn derivatization and capillary electrophoresis separation on a poly(dimethylsiloxane) (PDMS) microchip can be realized as efficient as those on glass microchips. In an optimized condition of micellar electrokinetic chromatography (MEKC), using 25 mM sodium borate buffer (pH 10.0) with 25 mM sodium dodecyl sulfate (SDS) and 5% v/v methanol, the electroosmotic flow in an oxidized PDMS microchip is stabilized within 3% for days. By employing a fluorometric derivatization with o‐phthaldialdehyde (OPA) in an optimally designed reaction chamber, four most important biogenic amines occurring in foods, histamine, tyramine, putrescine, and tryptamine, are quantitatively determined in less than 1 min at the levels applicable to real samples. The migration behaviors of anionic OPA‐derivatized biogenic amines under the MEKC conditions are analyzed, and it has been found that under our separation conditions, the electrophoretic mobility of the SDS micelles is significantly greater than those of the anions in the aqueous phase. The channel manifold in a PDMS substrate is fabricated using replica molding against a thick photoresist, SU‐8, pattern generated by photolithography. The plate with the microchannel pattern is strongly, irreversibly bonded to another PDMS plate by using a new bonding technique, which employs surface oxidation by corona discharge generated from a cheap, handy source, Tesla coil.

Adhesive and Dead Volume Free Interfacing between PDMS Microfluidic Channels

We have developed an adhesive and dead volume free poly(dimethylsiloxane) (PDMS) microfluidic channel interfacing technique through capillaries. Capillary zone electrophoresis (CZE) with a bare capillary and capillary electrochromatography (CEC) with a beads-packed separation column successfully separated fluorescein, FITC and coumarin440 and 450 respectively using the adhesive free feature.

Microchip-Based Simultaneous On-Line Monitoring of CR(III) and CR(VI) Using Highly Efficient Chemiluminescence Detection

We have developed a micromachined continuous flow analysis (CFA) device for the simultaneous detection of Cr(III) and Cr(VI) with chemiluminescence (CL). By selective injection of the reductant, we can determine the total Cr and Cr(III) quantitatively. Linearity for Cr(III) and Cr(VI) has been established over concentration ranges of 50 ∼ 500 ppb and 10 ∼ 1000 ppb, and detection limits (S/N = 3) are 10 ppb and 1.3 ppb respectively.

PDMS Microchip for Precolumn Reaction and Micellar Electrokinetic Chromatography of Biogenic Amines

We have developed a microchip to perform fast and efficient precolumn reactions and micellar electrokinetic chromatography (MEKC) of biogenic amines sequentially in poly(dimethylsiloxane) (PDMS). The relative mixing and reaction efficiencies of three different structures of precolumn reactors are investigated. The separation efficiency in a PDMS chip is comparable to that in a glass chip.

Rapid Precolumn Reaction and Chiral Separation on an Integrated Microchip

We have performed precolumn derivatization and chiral separation of D,L-amino acids on an integrated poly(dimethylsiloxane) (PDMS) microchip. Enantiomers of amino acids are labeled with o-phthaldialdehyde/2,3,4,6-tetra-O-acetyl-thio-β-D-glucopyranose (OPA/TATG) in the microfabricated reactor, and separated by micellar electrokinetic chromatography (MEKC) in an achiral environment. Optimized chiral separations are achieved within 100 s using a buffer consisting of 25 mM sodium borate (pH 10.0) and 15 mM sodium dodecyl sulfate (SDS). The resolutions of enantiomeric OPA/TATG-derivatized amino acids are in the range of 1.4 ~ 6.1.

Capillary Electrochromatography and Preconcentration of Neutral Compounds on PDMS Microchips

We have fabricated a chromatographic chamber with integrated frits on a poly(dimethylsiloxane) (PDMS) substrate for capillary electrochromatography (CEC). The channel networks are coated with polybrene and dextran sulfate to avoid adsorption of hydrophobic analytes to PDMS. The CEC chamber is packed with octadecylsilane (ODS) coated silica bead (5 urn diameter). Preconcentration and CEC of neutral compounds have been successfully performed in our PDMS microchip.

Rapid Sample Cleanup Microchip for Protein Analysis by Electrospray Ionization Mass Spectrometry

We have developed a simple, rapid sample cleanup method for the electrospray ionization (ESI) mass spectrometry of proteins by using a plastic microchip. Diffusion-based cleanup method between laminar flows offers effective removal of salts in about 1-second, and greatly enhanced signal-to-noise ratios of ESI mass spectrum.