Biomedical subjects

Jinseok Heo

Publications and source records attributed to Jinseok Heo.

5 recordsLinked to original sources

PubMed2006

Hybridization of DNA to bead-immobilized probes confined within a microfluidic channel.

We report the factors influencing the capture of DNA by DNA-modified microbeads confined within a microfluidic channel. Quantitative correlation of target capture efficiency to probe surface concentration, solution flow rate, and target concentration are discussed. The results indicate that the microfluidic system exhibits a limit of detection of approximately 10(-10) M (approximately 10(-16) mol) DNA and a selectivity factor of approximately 8 x 10(3). Typical hybridization times are on the order of minutes.

Biotinylation↗

PubMed2005

Microfluidic biosensor based on an array of hydrogel-entrapped enzymes.

Here we show that a microfluidic sensor based on an array of hydrogel-entrapped enzymes can be used to simultaneously detect different concentrations of the same analyte (glucose) or multiple analytes (glucose and galactose) in real time. The concentration of paraoxon, an acetylcholine esterase inhibitor, can be quantified using the same approach. The hydrogel micropatch arrays and the microfluidic systems are easy to fabricate, and the hydrogels provide a convenient, biocompatible matrix for the enzymes. Isolation of the micropatches within different microfluidic channels eliminates the possibility of cross talk between enzymes.

Acetylcholinesterase↗

PubMed2003

Measurement of enzyme kinetics using a continuous-flow microfluidic system.

This paper describes a microanalytical method for determining enzyme kinetics using a continuous-flow microfluidic system. The analysis is carried out by immobilizing the enzyme on microbeads, packing the microbeads into a chip-based microreactor (volume approximately 1.0 nL), and flowing the substrate over the packed bed. Data were analyzed using the Lilly-Hornby equation and compared to values obtained from conventional measurements based on the Michaelis-Menten equation. The two different enzyme-catalyzed reactions studied were chosen so that the substrate would be nonfluorescent and the product fluorescent. The first reaction involved the horseradish peroxidase-catalyzed reaction between hydrogen peroxide and N-acetyl-3,7-dihydroxyphenoxazine (amplex red) to yield fluorescent resorufin, and the second the beta-galactosidase-catalyzed reaction of nonfluorescent resorufin-beta-D-galactopyranoside to yield D-galactose and fluorescent resorufin. In both cases, the microfluidics-based method yielded the same result obtained from the standard Michaelis-Menten treatment. The continuous-flow method required approximately 10 microL of substrate solution and 10(9) enzyme molecules. This approach provides a new means for rapid determination of enzyme kinetics in microfluidic systems, which may be useful for clinical diagnostics, and drug discovery and screening.

Catalysis↗

PubMed2003

A microfluidic bioreactor based on hydrogel-entrapped E. coli: cell viability, lysis, and intracellular enzyme reactions.

Viable E. coli cells were entrapped in hydrogel micropatches photopolymerized within microfluidic systems. The microfluidic channels and the micropatches have sizes on the order of 100-500 microm. Small molecules, such as dyes and surfactants, present in the solution surrounding the hydrogel, are able to diffuse into the gel and encounter the cells, but the cells are sufficiently large to be retained. For example, sodium dodecyl sulfate is a lysis agent that is able to penetrate the hydrogel and disrupt the cellular membrane. Entrapment of viable cells within hydrogels, followed by lysis, could provide a convenient means for preparing biocatalysts without the need for enzyme extraction and purification. Hydrogel-immobilized cells are able to carry out chemical reactions within microfluidic channels. Specifically, a nonfluorescent dye, BCECF-AM, is able to penetrate both the hydrogel and the bacterial membrane and be converted into a fluorescent form (BCECF) by the interior cellular machinery. These results suggest that cells immobilized within microfluidic channels can act as sensors for small molecules and as bioreactors for carrying out reactions.

Bioreactors↗

PubMed2003

A large fibrous polyp of the gallbladder mimicking a polypoid carcinoma.

Fibrous polyp of the gallbladder is a rare variant of benign gallbladder polyp. Differentiation between a benign polyp and polypoid carcinoma of the gallbladder is often difficult when the polyp is more than 1 cm in diameter. We report a rare case of a large fibrous polyp of the gallbladder mimicking a carcinoma. A 44-year-old Korean woman who presented with abdominal pain was diagnosed with a large gallbladder polyp, measuring 1.26 cm in diameter, by abdominal ultrasonography. The lesion was echogenic with a nodular surface on ultrasonography, and showed contrast enhancement on computed tomography. Neither evidence of infiltration into the gallbladder wall nor lymph node enlargement was shown. The resected gallbladder showed a 1.2 x 0.8-cm-sized polyp with a nodular surface. Histologically, it showed a leaf-like configuration and loose or cellular connective stroma containing scattered duct-like structures, varying-sized vessels, and patchy infiltration of chronic inflammatory cells. Stromal cells were immunoreactive for vimentin and smooth-muscle actin and negative for S-100 protein and desmin. Large fibrous polyps of the gallbladder should be considered in the differential diagnosis of benign and malignant polypoid lesions of the gallbladder.

Adult↗