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Yoon-Bo Shim

Publications and source records attributed to Yoon-Bo Shim.

At least 19 recordsLinked to original sources
PubMed2006

An impedimetric immunosensor for the label-free detection of bisphenol A.

Label-free detection of bisphenol A based on the impedance measurement was achieved with an impedimetric immunosensor. The immunosensor was fabricated by the covalent bond formation between a polyclonal antibody and a carboxylic acid group functionalized onto a nano-particle comprised conducting polymer. By using a commercial reagent 4,4-bis(4-hydroxyphenyl) valeric acid (BHPVA), which has an analogous structure of BPA, we have prepared the antigen through the conjugation of BHPVA with bovine serum albumin (BSA) and then produced a specific polyclonal antibody. The immobilization of antibody and the interaction between antibody and antigen were studied using quartz crystal microbalance (QCM) and electrochemical impedance spectroscopic (EIS) techniques. The impedance and mass changes due to the specific immuno-interaction at the sensor surface were utilized to detect antigen and bisphenol A (BPA). The immunosensor showed specific recognition of BPA with less interference than 4.5% from other common phenolic compounds. Under an optimized condition, the linear dynamic range of BPA detection was between 1 and 100 ng/ml. The detection limit of bisphenol A was determined to be 0.3+/-0.07 ng/ml. The proposed immunosensor was applied to a human serum sample and the BPA concentration was determined by the standard addition method.

Antibodies, Monoclonal↗
PubMed2006

Direct analysis of trace phenolics with a microchip: in-channel sample preconcentration, separation, and electrochemical detection.

A micrototal analytical method assembling in-channel preconcentration, separation, and electrochemical detection steps has been developed for trace phenolic compounds. A micellar electrokinetic chromatography separation technique was coupled with two preconcentration steps of field-amplified sample stacking (FASS) and field-amplified sample injection (FASI). An amperometric detection method with a cellulose-dsDNA-modified, screen-printed carbon electrode was applied to detect preconcentrated and separated species at the end of the channel. The microchip was composed of three parallel channels: first, two are for the sample preconcentration using FASS and FASI methods, and the third one is for the separation and electrochemical detection. The modification of the electrode surface improved the detection performance by enhancing the signal-to-noise characteristic without surface fouling of the electrode. The method was examined for the analysis of eight phenolic compounds. Experimental parameters affecting the analytical performance of the method were assessed and optimized. The preconcentration factor was increased by about 5200-fold as compared with a simple capillary zone electrophoretic analysis using the same channel. Reproducible response was observed during multiple injections of samples with a RSD of <8.0%. The calibration plots were shown to be linear (with the correlation coefficient between 0.9913 and 0.9982) over the range of 0.4-600 nM. The sensitivity was between 0.17 +/- 0.001 and 0.48 +/- 0.006 nA/nM, with the detection limit of approximately 100 to approximately 150 pM based on S/N = 3. The applicability of the method to the direct analysis of trace phenolic compounds in water samples was successfully demonstrated.

Catalysis↗
PubMed2006

Electrochemical detection of mismatched DNA using a MutS probe.

A direct and label-free electrochemical biosensor for the detection of the protein-mismatched DNA interaction was designed using immobilized N-terminal histidine tagged Escherichia coli. MutS on a Ni-NTA coated Au electrode. General electrochemical methods, cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM) and impedance spectroscopy, were used to ascertain the binding affinity of mismatched DNAs to the MutS probe. The direct results of CV and impedance clearly reveal that the interaction of MutS with the CC heteroduplex was much stronger than that with AT homoduplex, which was not differentiated in previous results (GT > CT > CC approximately AT) of a gel mobility shift assay. The EQCM technique was also able to quantitatively analyze MutS affinity to heteroduplexes.

Base Pair Mismatch↗
PubMed2006

The biosensor based on the pyruvate oxidase modified conducting polymer for phosphate ions determinations.

An enzymatic biosensor was fabricated by the covalent immobilization of pyruvate oxidase (PyO) onto the nano-particle comprised poly-5,2':5',2''-terthiophene-3'-carboxylic acid, poly-TTCA (nano-CP) layers on a glassy carbon electrode (GCE) for the amperometric detection of the phosphate ions. The direct electron transfer reaction of the immobilized PyO onto the nano-CP layers was investigated and the electron transfer rate constant was determined to be 0.65 s(-1). The electrochemically prepared nano-CP lowered the oxidation potential (+0.40 V versus Ag/AgCl) of an enzymatically generated H(2)O(2) by PyO in a phosphate solution. Experimental parameters affecting the sensitivity of the biosensors, such as amounts of the cofactors, the pH, the applied potential, and the temperature were optimized. A linear response for the detection of the phosphate ion was observed between 1.0 microM and 100 microM and the detection limit was determined to be about 0.3 microM. The response time of the biosensors was about 6s. The biosensor showed good selectivity towards other interfering anions. The long-term storage stability of the phosphate biosensor was studied and the sensor was applied in a human serum sample for the phosphate ions detection.

Biosensing Techniques↗
PubMed2006

Lipid-bonded conducting polymer layers for a model biomembrane: application to superoxide biosensors.

Model biomembranes composed of poly-DATT/DGS/POPA and poly-DATT/DGS/CL were separately prepared on gold electrodes. A monolayer of 1,2-dioleoyl-sn-glycero-3-succinate (DGS) was covalently bonded onto electrochemically grown poly-(3,4-diamiono-2,2:5,2-terthiophene) (DATT) layers (thickness of approximately 300 nm; particle size of approximately 50 to 70 nm). The numbers of unit molecules of the poly-DATT layer and of the DGS immobilized onto the poly-DATT layers were 1.53 x 10(-7) and 1.56 x 10(-9) mol cm(-2), respectively, using a quartz crystal microbalance technique. The lipid bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphate (POPA) and cardiolipin (CL) were formed onto the poly-DATT/DGS layer using the Langmuir-Blodgett technique. The surface characterizations of each step were investigated by SEM, AFM, and XPS analyses. Cytochrome c (cyt c) was immobilized onto these model biomembranes through the charge interaction between the positive charges of cyt c and the negative charges of phosphate groups in CL or POPA lipids. At the POPA- and CL-modified biomembranes, the formal potentials of the redox couple of the immobilized cyt c were 0.22 and 0.23 V (vs Ag/AgCl), respectively. The redox reaction of the immobilized cyt c at the POPA- and CL-modified biomembranes was quasireversible, and the electron-transfer rate constants were 0.121 s(-1) and 0.133 s(-1), respectively. The applicability of these cyt c immobilized bioimitation membranes as the biosensors was tested for the determination of superoxide.

Adenosine↗
PubMed2006

Analysis of polymerase chain reaction amplifications through phosphate detection using an enzyme-based microbiosensor in a microfluidic device.

An electrochemical method was developed for analyzing PCR amplification through the detection of inorganic phosphates (Pi). This method coupled a microchip to a nanoparticle comprising poly-5,2'-5',2''-terthiophene-3'-carboxylic acid (poly-TTCA)/pyruvate oxidase (PyO) modified microbiosensor. It detects Pi produced from the pyrophosphate (PPi), which is released as a byproduct of PCR. After completion of PCR, PPi is hydrolyzed to Pi by inorganic pyrophosphatase. On the microbiosensor surface, pyruvate was converted to H2O2 by PyO in the presence of Pi and oxygen, and subsequently, the anodic current of enzymatically generated H2O2 was detected at +0.5 V versus Ag/AgCl. The CE-EC analysis was completed within 2 min in a coated channel with 75.0 mm separation length at the field strength of -200 V/cm. Excellent operation stability of poly-TTCA/PyO was observed for a long period of analysis. The reproducibility of the analysis yielded an RSD of 3.4% (n = 22) for the peak areas and 1.8% (n = 22) for the migration times. The sensitivity of the analysis was 0.59 +/- 0.01 nA/cycle with a regression coefficient of 0.971.

Biosensing Techniques↗
PubMed2006

Simultaneous analysis of nitrate and nitrite in a microfluidic device with a Cu-complex-modified electrode.

A CE microsystem coupled with a microchip and a copper-(3-mercaptopropyl) trimethoxysilane (Cu-MPS) complex-modified carbon paste electrode (CPE) was developed for the simultaneous analysis of nitrite and nitrate. The method is based on the electrocatalytic reduction of both analytes with the modified electrode. The Cu-MPS complex was characterized by voltammetric, XPS, and FT-IR analyses. Experimental parameters affecting the sensitivity of the modified electrode were assessed and optimized. The best separation was achieved in a 60 mm separation channel filled with a 20 mM acetate buffer of pH 5.0 containing 3.0 mM CTAB at separation field strength of -250 V/cm within 90 s. The detection potential for the simultaneous analysis of nitrite and nitrate was found to be -225 mV versus Ag/AgCl. A reproducible response (RSD of 3.2% (nitrite) and 2.8% (nitrate), n = 8) for repetitive sample injections reflected the negligible electrode fouling at the modified CPE. The interference effect was examined for other inorganic ions and biological compounds. A wide hydrodynamic range between 0.25 and 120 microM was observed for analyzing nitrite and nitrate with the sensitivities of 0.069 +/- 0.003 and 0.065 +/- 0.002 nA/microM, and the detection limits, based on S/N = 3, were found to be 0.09 +/- 0.007 and 0.08 +/- 0.009 microM, respectively. The applicability of the method to water and urine samples analyses was demonstrated.

Copper↗
PubMed2005

Functionalized conducting polymer as an enzyme-immobilizing substrate: an amperometric glutamate microbiosensor for in vivo measurements.

The functionalized conducting polymer (CP) of 5, 2':5', 2' '-terthiophene-3'-carboxylic acid on a platinum microelectrode was prepared through the electropolymerization process using cyclic voltammetry and was used as a substrate for the immobilization of enzymes. The nanoparticles of the CP were obtained at a high scan rate in the cyclic voltammetric experiment. A needle-type amperometric glutamate microbiosensor based on the covalent immobilization of glutamate oxidase (GlOx) onto the CP layer was fabricated for in vivo measurements. The surfaces of the CP/Pt and GlOx/CP/Pt were characterized by QCM, ESCA, and AFM. The biosensor efficiently detected glutamate through the oxidation of enzymatically generated H2O2 at approximately +0.45 V versus Ag/AgCl. Various experimental parameters, such as pH, temperature, and the applied potential in the detection step were optimized. The interference effects from other biological compounds were examined, and ascorbate and dopamine interferences were observed, which were completely minimized by coimmobilizing ascorbate oxidase and by coating the sensor surface with a cationic polymer, polyethyleneimine. A linear calibration plot for glutamate was obtained between 0.2 and 100 microM with a detection limit of 0.1 +/- 0.03 microM. The proposed glutamate microbiosensor was successfully used for in vivo monitoring of the extracellular glutamate released by cocaine stimulation.

Amino Acid Oxidoreductases↗
PubMed2005

A separation-free amperometric immunosensor for vitellogenin based on screen-printed carbon arrays modified with a conductive polymer.

A disposable amperometric immunosensor was studied for the rapid detection of carp (Carassius auratus) Vitellogenin (Vtg). The sensor was fabricated based on screen-printed carbon arrays (SPCAs) containing eight carbon working and an integrated carbon counter electrodes. To construct the sensor, a conducting polymer (poly-terthiophene carboxylic acid) was electropolymerized on the surface of working electrodes and the polymer-coated SPCAs was characterized by SEM. Horseradish peroxidase (HRP) and a monoclonal antibody (anti-Vtg) specific to carp Vtg were covalently attached onto the polymer modified SPCAs. The immobilization of HRP and anti-Vtg onto the polymer-coated SPCAs was examined using cyclic voltammetry and quartz crystal microbalance studies. In order to detect the amount of Vtg, glucose oxidase (GOx)-labelled Vtg bound to the sensor surface under competition with the Vtg analyte was quantified amperometrically using glucose as a substrate. The performance of the eight sensors in arrays was evaluated by obtaining the calibration plots for Vtg. The sensor arrays exhibit a linear range of the Vtg concentration from 0.25 to 7.8 ng/ml and the detection limit was determined to be 0.09 ng/ml. Furthermore, the performance of the immunosensor for the determination of Vtg was evaluated by a standard addition method performed in fish serum samples.

Animals↗
PubMed2005

Microchip capillary electrophoresis with a cellulose-DNA-modified screen-printed electrode for the analysis of neurotransmitters.

A microfluidic chip based on capillary electrophoresis coupled with a cellulose-single-stranded DNA (cellulose-ssDNA) modified electrode was used for the simultaneous analysis of dopamine (DA), norepinephrine (NE), 3,4-dihydroxy-L-phenylalanine (L-DOPA), 3,4-dihydroxyphenylacetic acid (DOPAC), and ascorbic acid (AA). The modification of the electrode improved the electrophoretic analysis performance by lowering the detection potential and enhancing the signal-to-noise characteristic without surface poisoning of the electrode. The sensitivity of the modified electrode was about 12 times higher than those of the bare ones. The test compounds were separated using a 62 mm long separation channel at the separation field strength of +200 V/cm within 220 s in a 10 mM phosphate buffer (pH 7.4). The most favorable potential for the amperometric detection was 0.7 V (vs. Ag/AgCl). A reproducible response (relative standard deviation of 1.3, 1.3, 2.1, 3.1, 3.4% for DA, NE, L-DOPA, DOPAC, and AA, respectively, for n = 9) for repetitive sample injections reflected the negligible electrode fouling at the cellulose-ssDNA modified electrode. Square-wave voltammetric analyses reflected the sensitivities of the modified electrode for DA, NE, L-DOPA, DOPAC, and AA which were 1.78, 0.82, 0.69, 2.45, and 1.23 nC/microM with detection limits of 0.032, 0.93, 1.13, 0.31, and 0.62 microM, respectively. The applicability of this microsystem to real sample analysis was demonstrated.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2005

Detection of polymerase chain reaction fragments using a conducting polymer-modified screen-printed electrode in a microfluidic device.

A simple and fast method for electrochemical detection of amplified fragments by PCR was successfully developed using CE in a microfluidic device with a modified screen-printed carbon electrode (SPCE). The surfaces of the SPCE were modified with poly-5,2'-5',2''-terthiophene-3'-carboxylic acid, which improves the analysis performance by lowering the detection potential, enhancing the S/N characteristics, and avoiding electrode poisoning. DNA fragments amplified by PCR were separated within 210 s in a 75.5 mm-long coated-separation channel at a separation field strength of -200 V/cm. To minimize the sample adsorption into the inner surface of the capillary wall, which disturbs the separation, a dynamically coated capillary with an acrylamide solution was used. Furthermore, the analysis procedure was simplified and rendered reproducible by using 0.50% w/v hydroxyethylcellulose as a separation matrix in a coated channel. The reproducibility of the analysis employing the coated channel yielded RSD of 4.3% for the peak areas and 1.4% for the migration times in eight repetitive measurements at a modified electrode, compared with 21.3 and 9.4% for a bare electrode. The sensitivity of the assay was 18.74 pAs/(pg/microL) with a detection limit of 584.31 +/- 1.3 fg/microL.

Drug Stability↗
PubMed2004

The potential use of hydrazine as an alternative to peroxidase in a biosensor: comparison between hydrazine and HRP-based glucose sensors.

The potential use of hydrazine sulfate was examined for the catalytic reduction of enzymatically generated H2O2 in a biosensor system. The performance of the hydrazine-based sensor was compared with an HRP-based glucose sensor as a model of a biosensor. Hydrazine and HRP were covalently immobilized onto a conducting polymer layer with glucose oxidase. The direct electron transfer reactions of the immobilized hydrazine and HRP onto the poly-5,2':5,2''-terthiophene-3'-carboxylic acid (poly-TTCA) layer were investigated by using cyclic voltammetric method and the electron transfer rate constants were determined. The glucose oxidase- and hydrazine-immobilized sensor efficiently reduced the enzymatically generated H2O2 at -0.15 V versus Ag/AgCl. The surface of this GOx/hydrazine/poly-TTCA-based glucose sensor was characterized by QCM, SEM, and ESCA. Glucose-sensing properties were studied using cyclic voltammetric and chronoamperometric techniques. Various experimental parameters were optimized according to the amount of hydrazine, pH, the temperature, and the applied potential. A linear calibration plot was obtained in the concentration range between 0.1 and 15.0 mM, and the detection limit was determined to be 40.0+/-7.0 microM. Interferences from other biological compounds were studied. The long-term stability of the GOx/hydrazine sensor was better than that of the one based on a GOx/HRP biosensor. The proposed glucose sensor was successfully applied to human whole blood and urine samples for the detection of glucose.

Biosensing Techniques↗
PubMed2004

Development of a new and simple method for the detection of histidine-tagged proteins.

To develop a general method for the detection of histidine-tagged proteins, the interactions of the histidine epitope tag of MutH and MutL proteins with the epitope specific monoclonal anti-His6 antibody were monitored by a label-free direct method using impedance spectroscopy. The immunosensor was fabricated by covalent coupling of the antibody on a conducting polymer coated electrode surface. The impedance of the antibody modified electrode was decreased after binding to the histidine-tagged proteins. The specificity of the sensor was demonstrated by showing that no impedance change was occurred when the sensor was exposed to both of non-tagged MutH and MutL proteins. The specific interaction was further characterized using quartz crystal microbalance studies. Based on impedance measurements, the linear ranges were obtained from 50.0 to 125.0 and 50.0 to 250.0 micorg/ml, for His-tag MutH and His-tag MutL proteins, respectively. The detection limits were determined to be 37.8 and 59.1 microg/ml, for His-tag MutH and His-tag MutL proteins, respectively.

Adenosine Triphosphatases↗
PubMed2004

A lipophilic sol-gel matrix for the development of a carbonate-selective electrode.

Organic-inorganic hybrid sol-gel matrixes were used as hosts for trifluoroacetyl-p-decylbenzene (TFADB), a traditional ionophore for carbonate. The sol-gel precursor was prepared by the reaction of (3-isocyanopropyl)triethoxysilane with ethylene glycol. Hexadecyltrimethoxysilane (HDTMOS) was employed as a co-precursor. An appropriate amount of tridodecylmethylammonium chloride (TDMAC) and 2-nitrophenyloctyl ether (NPOE) were used as membrane components. On mixing with an acidic catalyst, the sol-state precursors slowly gelled, yielding a membrane in which the active components, TFADB and TDMAC, were encapsulated. Infrared, (1)H, and (29)Si MAS NMR spectrometers were employed to monitor the sol-gel process and the degree of polymerization. The performances of the sol-gel membrane-based electrodes were compared to those of TFADB-based poly(vinyl chloride) (PVC) membrane electrodes. Membranes with a molar ratio of TFADB:TDMAC (1:0.14) showed extended lifetime and stable baseline potential. The response slope toward carbonate was approximately 27 mV/decade between 10(-)(5) and 10(-)(3.5) M at 18 degrees C. Interestingly, selectivity toward carbonate over salicylate and other lipophilic anions was improved, clearly deviating from the Hofmeister selectivity pattern. Responses toward small inorganic anions including chloride and sulfate were negligible. The selectivity coefficients measured by the matched potential method in 0.1 M tris-sulfuric acid buffer, pH 8.75, were log = -0.3, log = -4.2, and log = -2.5.

Journal Article↗
PubMed2004

Detection of protein-DNA interaction with a DNA probe: distinction between single-strand and double-strand DNA-protein interaction.

A simple, direct method for the detection of DNA-protein interaction was developed with electrochemical methods. Single-stranded DNA (ss-DNA) probes were prepared through the chemical bonding of an oligonucleotide to a polymer film bearing carboxylic acid groups, and double-stranded DNA (ds-DNA) probes were prepared through hybridization of the complementary sequence DNA on the ss-DNA probe. Impedance spectroscopy and differential pulse voltammetry (DPV) distinguished the interaction between the DNA probes with mouse Purbeta (mPurbeta), an ss-DNA binding protein, and with Escherichia coli MutH, a ds-DNA binding protein. Impedance spectra obtained before and after the interaction of DNA probes with these proteins clearly showed the sequence-specific ss-DNA preference of mPurbeta and the sequence-specific ds-DNA preference of MutH. The concentration dependence of proteins on the response of the DNA probes was also investigated, and the detection limits of MutH and mPurbeta were 25 and 3 microg/ml, respectively. To confirm the impedance results, the variation of the current oxidation peak of adenine of the DNA probe was monitored with DPV. The formation constants of the complexes formed between the probe DNA and the proteins were estimated based on the DPV results.

DNA↗
PubMed2004

A performance comparison of choline biosensors: anodic or cathodic detections of H2O2 generated by enzyme immobilized on a conducting polymer.

Amperometric choline biosensors were fabricated by the covalent immobilization of an enzyme of choline oxidase (ChO) and a bi-enzyme of ChO/horseradish peroxidase (ChO/HRP) onto poly-5,2':5',2"-terthiophene-3'-carboxylic acid (poly-TTCA) modified electrodes (CPMEs). A sensor modified with ChO utilized the oxidation process of enzymatically generated H(2)O(2) in a choline solution at +0.6V. The other one modified with ChO/HRP utilized the reduction process of H(2)O(2) in a choline solution at -0.2V. Experimental parameters affecting the sensitivity of sensors, such as pH, applied potential, and temperature were optimized. A performance comparison of two sensors showed that one based on ChO/HRP/CPME had a linear range from 1.0 x 10(-6) to 8.0 x 10(-5) M and the other based on ChO/CPME from 1.0 x 10(-6) to 5.0 x 10(-5) M. The detection limits for choline employing ChO/HRP/CPME and ChO/CPME were determined to be about 1.0 x 10(-7) and 4.0 x 10(-7) M, respectively. The response time of sensors was less than 5s. Sensors showed good selectivity to interfering species. The long-term storage stability of the sensor based on ChO/HRP/CPME was longer than that based on ChO/CPME.

Alcohol Oxidoreductases↗
PubMed2004

Selective binding of NH4 + by redox-active crown ethers: application to a NH4 + sensor.

Two redox-active crown ethers, (1,1'- bi-2-naphthyl)-23-crown-6 incorporating 9,10-anthraquinone (BNAQ) and 1,4-benzoquinone (BNBQ), were synthesized and employed in the selective binding of NH(4)(+) over K(+). Their applications to NH(4)(+) detection were studied by cyclic voltammetry and amperometry in aqueous media. The results showed that the magnitude of the quinone redox peak decreased linearly as the concentration of NH(4)(+) increased, indicating the formation of BNAQ-NH(4)(+) and BNBQ-NH(4)(+) complexes. Formation constants of BNAQ-NH(4)(+) and BNBQ-NH(4)(+) complexes were determined to be 4.3 x 10(3) and 4.0 x 10(3) M(-1), respectively, which were 2 orders of the magnitude greater than those of BNAQ-K(+) and BNBQ-K(+) complexes. The (1)H NMR titration method carried out in DMSO-d(6) showed that both complexes possessed 1:1 stoichiometry, and association constants were determined to be 648 +/- 35 and 600 +/- 47 M(-1) for BNAQ-NH(4)(+) and BNBQ-NH(4)(+), respectively. Interference effects from other alkali and alkaline earth metal ions in the analysis of NH(4)(+) were also investigated. The BNAQ-modified sensor showed a linear response from 1.0 microM to 1.0 mM for NH(4)(+), and the detection limit was determined to be 0.9 +/- 0.03 microM.

Anthraquinones↗