Biomedical subjects

Hyun C Yoon

Publications and source records attributed to Hyun C Yoon.

9 recordsLinked to original sources

PubMed2005

A strategy for sensitivity and specificity enhancements in prostate specific antigen-alpha1-antichymotrypsin detection based on surface plasmon resonance.

A biochip based on surface plasmon resonance was fabricated to detect prostate specific antigen-alpha(1)-antichymotrypsin (PSA-ACT complex) in both HBS buffer and human serum. To reduce non-specific binding and steric hindrance effect, the chemical surface of the sensor chips was constructed by using various oligo(ethylene glycol) mixtures of different molar ratios of HS(CH2)11(OCH2CH2)6OCH2COOH and HS(CH2)11(OCH2CH2)3OH. The self-assembled monolayers were biotinylated to facilitate the immobilization of streptavidin. Using the chip surfaces, PSA-ACT complex in HBS buffer and human serum was detected at 20.7 and 47.5 ng/ml by primary immunoresponse, respectively. However, the limit of detection could be simply enhanced by a sandwich strategy to improve the sensitivity and specificity of the immunoassay. An intact PSA polyclonal antibody was used as an amplifying agent in the strategy. As a result, PSA-ACT complex concentrations as low as 10.2 and 18.1 ng/ml were found in the HBS buffer and human serum sample, respectively. The result indicates that this approach could satisfy our goal without modifying the secondary interactant.

Biotin↗

PubMed2005

Bioelectrocatalytic signaling from immunosensors with back-filling immobilization of glucose oxidase on biorecognition surfaces.

We report a novel method of electrochemical signaling from antigen-antibody interactions at immunoelectrodes with bioelectrocatalyzed enzymatic signal amplification. For the immunosensing surface construction, a poly(amidoamine) G4-dendrimer was employed not only as a building block for the electrode surface modification but also as a matrix for ligand functionalization. As a model biorecognition reaction, the dinitrophenyl (DNP) antigen-functionalized electrode was fabricated and an anti-DNP antibody was used. Glucose oxidase (GOX) was chosen to amplify electrochemical signal by enzymatic catalysis. The signal amplification strategy introduced in this study is based on the back-filling immobilization of biocatalytic enzyme to the immunosensor surface, circumventing the use of an enzyme-labeled antibody. The non-labeled native antibody was biospecifically bound to the immobilized ligand, and the activated enzyme (periodate-treated GOX) reacted and "back-filled" the remaining surface amine groups on the dendrimer layer by an imine formation reaction. From the bioelectrocatalyzed signal registration with the immobilized GOX, the surface density of biospecifically bound antibody could be estimated. The DNP functionalization reaction was optimized to facilitate the antibody recognition and signaling reactions, and approximately 6% displacement of surface amine to DNP was found to be an optimum. From quartz crystal microbalance measurement, immunosensing reaction timing and the surface inertness to the nonspecific biomolecular binding were tested. By changing the surface functionalization level of DNP in the calibration experiments, immunosensors exhibited different dynamic detection ranges and limits of detection, supporting the capability of parameters modulation for the immunosensors. For the anti-DNP antibody assay, the fabricated immunosensor having 65% functionalization ratio exhibited the linear detection range of 10(-4) to 0.1 g/L protein and a limit of detection around 2 x 10(-5) g/L.

2,4-Dinitrophenol↗

PubMed2005

Inhibition assay of biomolecules based on fluorescence resonance energy transfer (FRET) between quantum dots and gold nanoparticles.

An inhibition assay method was developed based on the modulation in the FRET efficiency between quantum dots (QDs) and gold nanoparticles (AuNPs) in the presence of the molecules which inhibit the interactions between QD- and AuNP-conjugated biomolecules. For the functionalization, AuNPs were first stabilized by chemisorption of n-alkanethiols and then capped with the first generation polyamidoamine (G1 PAMAM) dendrimers. By employing a streptavidin-biotin couple as a model system, avidin was quantitatively analyzed as an inhibitor by sensing the change in photoluminescence (PL) quenching of SA-QDs by biotin-AuNPs. The detection limit for avidin was about 10 nM. It is anticipated that the PL quenching-based sensing system can be used for the quantitative analysis and high throughput screening of molecules which inhibit the specific biomolecular interactions.

Avidin↗

PubMed2005

Multichannel surface plasmon resonance imaging and analysis of micropatterned self-assembled monolayers and protein affinity interactions.

Multichannel images of 11-mercaptoundecanoic acid and 11-mercapto-1-undecanol self-assembled monolayers together with a biospecific interferon-gamma (IFN-gamma)/anti-IFN-gamma antibody immunoaffinity interaction were observed by the two-dimensional surface plasmon resonance (2D-SPR) imaging system. With the fabricated 2D-SPR imaging system, adopting a white light source in combination with a narrow band-pass filter, sharp images were resolved, minimizing the diffraction patterns on the resulting images. Micropatterning of self-assembled monolayers was acheived by exploiting the UV photolysis of thiol bonding, instead of conventional photolithography. The line profile calibration of the image contrast with ellipsometric analysis enabled us to discriminate the change in monolayer thickness within a sub-nanometer scale. For the protein interactions on the surface, the biospecific affinity recognition reaction of IFN-gamma antigen with surface-immobilized antibody was analyzed. Through the signal amplification strategy based on the enzyme-catalyzed precipitation reaction in a sandwich-type immunoassay, biospecific antigen binding was found detectable down to a concentration of 1 ng/mL.

Proteins↗

PubMed2004

Ferritin immunosensing on microfabricated electrodes based on the integration of immunoprecipitation and electrochemical signaling reactions.

A signal registration strategy from micropatterned immunosensors that converts antigen-antibody binding reactions into electrochemical signals was demonstrated. An array-type micropatterned gold electrode on a silicon wafer was fabricated, containing two electrode geometries of rectangular (100 microm x 500 microm) and circular (r. 50 microm) types, exhibiting electrochemical characteristics of bulk and micro-electrodes, respectively. Ferritin was employed as a model analyte for immunosensing because it has an advantageous molecular structure for functionalization to the sensing interface, and is regarded as a general marker protein for tumors and cancer recurrence. With the fabricated and ferritin-functionalized immunosensors, biospecific interactions were performed with antiferritin antiserum and secondary antibody samples, followed by electrochemical signaling via an immunoprecipitation reaction by the label enzyme. Under the optimized affinity-surface construction steps and reaction conditions, both types of microfabricated electrodes exhibited well-defined calibration results as a function of the protein concentration in antiserum samples. Furthermore, circular-type micropatterned immunoelectrodes exhibited voltammetric characteristics of microelectrodes, which is advantageous in terms of sensor operation under a fixed potential and low signal drift during the signaling reaction compared with the bulk-type electrodes. The results support that the employed signaling method with the proposed immunosensor configuration is fit for sensor miniaturization and integration to future biomicrosystems.

Antigen-Antibody Reactions↗

PubMed2003

A polymer-based microfluidic device for immunosensing biochips.

This paper describes the design, fabrication, and test of a PDMS/PMMA-laminated microfluidic device for an immunosensing biochip. A poly(dimethyl siloxane)(PDMS) top substrate molded by polymer casting and a poly(methyl methacrylate)(PMMA) bottom substrate fabricated by hot embossing are bonded with pressure and hermetically sealed. Two inlet ports and an air vent are opened through the PDMS top substrate, while gold electrodes for electrochemical biosensing are patterned onto the PMMA bottom substrate. The analyte sample is loaded from the sample inlet port to the detection chamber by capillary force, without any external intervening forces. For this and to control the time duration of sample fluid in each compartment of the device, including the inlet port, diffusion barrier, reaction chamber, flow-delay neck, and detection chamber, the fluid conduit has been designed with various geometries of channel width, depth, and shape. Especially, the fluid path has been designed so that the sample flow naturally stops after filling the detection chamber to allow sufficient time for biochemical reaction and subsequent washing steps. As model immunosensing tests for the microfluidic device, functionalizations of ferritin and biotin to the sensing surfaces on gold electrodes and their biospecific interactions with antiferritin antiserum and streptavidin have been investigated. An electrochemical detection method for immunosensing by biocatalyzed precipitation has been developed and applied for signal registration. With the biochip, the whole immunosensing processes could be completed within 30 min.

Antibodies↗

PubMed2002

Development of a screen-printed amperometric biosensor for the determination of L-lactate dehydrogenase level.

We attempted to develop a screen-printed biosensor for the amperometric determination of L-lactate dehydrogenase (LDH) level on the basis of NAD(+)/NADH-dependent dehydrogenase reaction. The printing ink for the working electrode consisted of L-lactate, NAD(+), composite polymer of hydroxyethyl cellulose with ethylene glycol, 3,4-dihydroxybenzaldehyde (3,4-DHB) as an electron transferring mediator, and graphite as the conducting material. The 3,4-DHB was electropolymerized on the carboneous working electrode by potential cycling between -200 and +300 mV vs. Ag/AgCl reference electrode. Through the electrocatalytic reaction with immobilized 3,4-DHB, the NADH generated by the LDH reaction could be efficiently oxidized at lower potential than the unmodified carbon electrode. The analytical performance of the electrode was characterized in terms of linear sensing range and detection limit for LDH. The response from the developed biosensor was linear up to 500 U/l of LDH, and the detection limit of 50 U/l was observed at the signal-to-noise ratio of 3.

Biosensing Techniques↗

PubMed2002

Biocatalytic precipitation induced by an affinity reaction on dendrimer-activated surfaces for the electrochemical signaling from immunosensors.

We have developed a strategy of signal generation for immunosensors that transduces biospecific affinity recognition reactions into electrochemical signals. The cyclic voltammetric method, tracking the precipitation of insoluble products onto the sensing surface and the subsequent decrement in the electrode area, was chosen for signal registration. Precipitation of insolubilities was induced by the catalytic reaction of enzymes, which were labeled to the biospecifically attached protein or antibody molecules. As a model system for affinity recognition, we have investigated the functionalization of biotin groups to the sensing monolayer and their biospecific interactions with anti-biotin antibody molecules. The immunosensing interface was developed onto the dendrimer-activated self-assembled monolayers (SAMs), as the base template for the functionalization of the antigen moiety and signal generation. The advantages of using dendrimer-activated SAMs in comparison to the plain modified thiolate SAMs for the sensing surface were shown in terms of sensing performances, and the analytical characteristics of the resulting immunosensor were examined. Additionally, the sensing system was applied for biotin/(strept)avidin couples, extending the applicability of the developed strategy.

Anti-Bacterial Agents↗

PubMed2002

Stepwise surface regeneration of electrochemical immunosensors working on biocatalyzed precipitation.

A new strategy of stepwise surface regeneration for electrochemical immunosensors, working on a biocatalyzed precipitation reaction, has been developed. The strategy is based on the combination of deposited product thin-film dissolution and bound-protein displacement reactions from the modified sensor surfaces. As a model system, surfaces functionalized with biotin groups and their affinity recognition/ displacement reactions with antibiotin antibody molecules were chosen and investigated for affinity-sensing and stepwise regeneration reactions.

Antibodies↗