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Biomedical subjects

Joseph Wang

Publications and source records attributed to Joseph Wang.

At least 55 records · Page 3Linked to original sources
PubMed2004

Carbon-nanotube-modified electrodes for amplified enzyme-based electrical detection of DNA hybridization.

Carbon-nanotube-modified glassy carbon (CNT/GC) transducers have been developed for enhancing the sensitivity and stability of enzyme-based electrochemical bioassays of DNA hybridization. The amplified signal reflects the interfacial accumulation of phenolic products of the alkaline-phosphatase tracer onto the CNT layer. In particular, chronopotentiometric measurements (following short accumulation periods) offer a substantial enhancement of the response of enzymatically liberated alpha-naphthol. The CNT modifier also leads to a dramatic improvement in the stability of the amperometric response of alpha-naphthol. These advantages of CNT/GC electrodes are illustrated from comparison to unmodified glassy carbon electrodes. Factors influencing the adsorptive accumulation of alpha-naphthol, and the overall performance of the new DNA assay, are assessed and optimized. The attractive performance characteristics of the new multi-amplification electrochemical detection of DNA hybridization are reported in connection to the detection of nucleic acid sequences related to the breast cancer BRCA1 gene.

Alkaline Phosphatase↗
PubMed2004

Microchip capillary electrophoresis with amperometric detection for rapid separation and detection of phenolic acids.

A microchip capillary-electrophoresis protocol for rapid and effective measurements of food-related phenolic acids (including chlorogenic, gentisic, ferulic, and vanillic acids) is described. Relevant parameters of the chip separation and amperometric detection are examined and optimized. Under optimum conditions, the analytes could be separated and detected in a 15 mM borate buffer (pH 9.5, with 10% of methanol) within 300 s using a separation voltage of 2000 V and a detection voltage of +1.0 V. Linear calibration plots are observed for micromolar concentrations of the phenolic acid compounds. The negligible sample volumes used in the microchip procedure obviates surface fouling common to amperometric measurements of phenolic compounds. The new microchip protocol offers great promise for a wide range of food applications requiring fast measurements and negligible sample consumption. An application on a commercial red wine was performed with minimal sample preparation and promising results.

Buffers↗
PubMed2004

Microchip capillary electrophoresis with electrochemical detection of thiol-containing degradation products of V-type nerve agents.

A microchip protocol for the capillary electrophoresis separation and electrochemical detection of thiol-containing degradation products of V-type nerve agents is described. The microchip assay relies on the derivatization reaction of 2-(dimethylamino)ethanethiol (DMAET), 2-(diethylamino)ethanethiol (DEAET), and 2-mercaptoethanol (ME) with o-phthaldialdehyde in the presence of the amino acid valine along with amperometric monitoring of the isoindole derivatives. Both off-chip and on-chip derivatization reactions have led to highly sensitive and rapid detection of the thiol degradation products. Various parameters influencing the derivatization, separation, and detection processes were examined and optimized. These include the amino acid co-reagent, reagent-mixing ratio, reaction time, injection time, separation voltage, and detection potential. The chip microsystem offers a rapid (<4 min) simultaneous detection of micromolar concentrations of DMAET, DEAET, and ME. Linear calibration plots were observed for the V-type nerve agent thiol degradation products, along with good stability and reproducibility (RSD < 8.0%). Detection limits of 5 and 8 microM were obtained for the off-chip reaction of DMAET and DEAET, respectively, following a 2-s injection. The suitability for assays of environmental matrixes was demonstrated for the determination of DMAET and DEAET in untreated tap and river water samples. The favorable analytical performance makes the new microfluidic device attractive for addressing the needs of various security scenarios.

Biodegradation, Environmental↗
PubMed2004

Electrochemical detection of amino acids at carbon nanotube and nickel-carbon nanotube modified electrodes.

The oxidation and enhanced detection of traditionally 'non-electroactive' amino acids at a single-wall carbon nanotube (SWNT) surface and at a nickel hydroxide film electrochemically deposited and generated upon the SWNT layer is reported. Different CNT are compared, with Nafion-dispersed SWNT offering the most favorable layer for constant-potential amperometric detection. Factors affecting the oxidation process, including the pH or applied potential, are assessed. The response of the SWNT-Nafion coated electrode compares favorably with that of copper and nickel disk electrodes under flow injection analysis (FIA) conditions. The electrodeposition of nickel onto the SWNT-Nafion layer (Ni-CNT) led to a dramatic enhancement of the analytical response (vs. that observed at the SWNT or nickel electrodes alone). The oxidative process at the Ni(OH)(2) layer has been studied and the increase in sensitivity rationalized. In the presence of amino acid the Ni-CNT layer undergoes an electrocatalytic process in which the amino acid reduces the newly formed NiO(OH) species. Furthermore, the attractive response of both the CNT and Ni-CNT layers has allowed these electrodes to be used for constant-potential FIA of various amino acids and indicates great promise for monitoring chromatographic effluents. Once again an improved signal was observed at the Ni-CNT electrode compared to nickel deposited upon a bare glassy carbon electrode (Ni-GC).

Amino Acids↗
PubMed2004

Biocatalytic carbon paste sensors based on a mediator pasting liquid.

The preparation and advantages of a new generation of carbon paste enzyme electrodes where the redox mediator acts also as the pasting liquid are described. The mediator pasting liquid concept is illustrated for amperometric biosensing of glucose in connection with either the tert-pentylferrocene or n-butylferrocene mediator/binder along with the glucose oxidase enzyme. The attractive performance and advantages of the new device is indicated from comparison to a conventional carbon paste biosensor using a mineral oil binder and the dimethylferrocene electron acceptor. The simplified preparation of the biosensor is coupled with a greatly improved sensitivity and an extended linear range. The mediator pasting liquid imparts high thermal stability onto the embedded enzyme and leads to good resistance to oxygen effects. Owing to the huge mediator reservoir, stability problems associated with the leaching of the mediator are greatly reduced. The fundamental aspects of the electrode behavior have been examined first in the absence of the enzyme. Variables affecting the performance of the new carbon paste biosensor have been investigated and optimized. Such use of the electron acceptor as a binder as well as the mediator offers considerable promise for the biosensing of numerous analytes of clinical and environmental significance.

Biosensing Techniques↗
PubMed2004

Electrochemical sensors for environmental monitoring: design, development and applications.

The advancement in miniaturization and microfabrication technology has led to the development of sensitive and selective electrochemical devices for field-based and in situ environmental monitoring. Electrochemical sensing devices have a major impact upon the monitoring of priority pollutants by allowing the instrument to be taken to the sample (rather than the traditional way of bringing the sample to the laboratory). Such devices can perform automated chemical analyses in complex matrices and provide rapid, reliable and inexpensive measurements of a variety of inorganic and organic pollutants. Although not exhaustive due to the vast amounts of new and exciting electrochemical research, this review addresses many important advances in electrochemical sensor design and development for environmental monitoring purposes. Critical design factors and development issues including analytical improvements (e.g. detection limits), microfabrication and remote communication are presented. In addition, modern environmental applications will be discussed and future perspectives considered.

Biosensing Techniques↗
PubMed2004

Carbon-nanotube/copper composite electrodes for capillary electrophoresis microchip detection of carbohydrates.

The preparation of carbon nanotube (CNT)/copper composite electrodes, based on co-mixing CNT and Cu powders within mineral oil, is described. The new composite electrode is used for improved amperometric detection of carbohydrates following their capillary electrophoresis (CE) microchip separations. The CNT/Cu composite electrode detector displays enhanced sensitivity compared to detectors based on copper or CNT alone. The marked catalytic action of the CNT/Cu composite material permits effective low potential (+0.5 V vs. Ag/AgCl) amperometric detection, and is coupled to the renewability, bulk modification and versatility advantages of composite electrodes. The CNT/Cu composite surface also leads to a greater resistance to surface fouling compared to that observed at the copper electrode. Factors affecting the electrocatalytic activity and the CE microchip detection are examined and optimized. The CNT/Cu composite electrode is also shown to be useful for the detection of amino acids as indicated from preliminary results. While the present work has focused on the enhanced CE microchip detection of carbohydrates and amino acids, the CNT/metal-composite electrode route should benefit the detection of other important groups of analytes.

Amino Acids↗
PubMed2004

Fast and simple sample introduction for capillary electrophoresis microsystems.

A newly designed capillary electrophoresis (CE) microchip with a simple and efficient sample introduction interface is described. The sample introduction is carried out directly on the separation channel through a sharp inlet tip placed in the sample vial, without an injection cross, complex microchannel layouts or hardware modification. Alternate placement of the inlet tip in vials containing the sample and buffer solutions permits a volume defined electrokinetic sample introduction. Such fast and simple sample introduction leads to highly reproducible signals with no observable carry over between different analyte concentrations. The performance of the system was demonstrated in flow-injection and CE measurements of nitroaromatic explosives and for on-chip enzymatic assays of glucose in the presence of ascorbic acid. Employing an 8 cm long separation channel and a separation voltage of 4000 V it offers high-throughput flow-injection assays of 100 samples h(-1) with a relative standard deviation of 3.7% for TNT (n= 100). Factors influencing the analytical performance of the new microchip have been characterized and optimized. Such ability to continuously introduce discrete samples into micrometer channels indicates great promise for high-speed microchip analysis.

Electrophoresis, Capillary↗
PubMed2004

Fabrication of poly(methyl methacrylate) microfluidic chips by atmospheric molding.

A greatly simplified method for fabricating poly(methyl methacrylate) (PMMA) separation microchips is introduced. The new protocol relies on UV-initiated polymerization of the monomer solution in an open mold under ambient pressure. Silicon microstructures are transferred to the polymer substrate by molding a methyl methacrylate solution in a sandwich (silicon master/Teflon spacer/glass plate) mold. The chips are subsequently assembled by thermal sealing of the channel and cover plates. The new fabrication method obviates the need for specialized replication equipment and reduces the complexity of prototyping and manufacturing. Variables of the fabrication process were assessed and optimized. The new method compares favorably with common fabrication techniques, yielding high-quality devices with well-defined channel and injection-cross structures, and highly smoothed surfaces. Nearly 100 PMMA chips were replicated using a single silicon master, with high chip-to-chip reproducibility (relative standard deviations of 1.5 and 4.7% for the widths and depths of the replicated channels, respectively). The relatively high EOF value of the new chips (2.12 x 10(-4) cm(2) x V(-1) x s(-1)) indicates that the UV polymerization process increases the surface charge and hence enhances the fluidic transport. The attractive performance of the new CE microchips has been demonstrated in connection with end-column amperometric and contactless-conductivity detection schemes. While the new approach is demonstrated in connection with PMMA microchips, it could be applied to other materials that undergo light-initiated polymerization. The new approach brings significant simplification of the process of fabricating PMMA devices and should lead to a widespread low-cost production of high-quality separation microchips.

Journal Article↗
PubMed2004

Whole cell-enzyme hybrid amperometric biosensor for direct determination of organophosphorous nerve agents with p-nitrophenyl substituent.

In this paper, we reported the construction of a hybrid biosensor for direct, highly selective, sensitive, and rapid quantitative determination of organophosphate pesticides with p-nitrophenyl substituent using purified organophosphorus hydrolase (OPH) for the initial hydrolysis and Arthrobacter sp. JS443 for subsequent p-nitrophenol oxidation. The biocatalytic layer was prepared by co-immobilizing Arthrobacter sp. JS443 and OPH on a carbon paste electrode. OPH catalyzed the hydrolysis of organophosphorus pesticides with p-nitrophenyl substituent such as paraoxon and methyl parathion to release p-nitrophenol that was oxidized by the enzymatic machinery of Arthrobacter sp. JS443 to carbon dioxide through electroactive intermediates 4-nitrocatechol and 1,2,4-benzenetriol. The oxidization current of the intermediates was measured and correlated to the concentration of organophosphates. The best sensitivity and response time were obtained using a sensor constructed with 0.06 mg dry weight of cell and 965 IU of OPH operating at 400 mV applied potential (vs. Ag/AgCl reference) in 50 mM citrate-phosphate pH 7.5 buffer at room temperature. Using these conditions, the biosensor measured as low as 2.8 ppb (10 nM) of paraoxon and 5.3 ppb (20 nM) of methyl parathion without interference from phenolic compounds, carbamate pesticides, triazine herbicides, and organophosphate pesticides that do not have the p-nitrophenyl substituent. The biosensor had excellent operational life-time stability with no decrease in response for more than 40 repeated uses over a 12-h period when stored at room temperature, while its storage life was approximately 2 days when stored in the operating buffer at 4 degrees C.

Actinobacteria↗
PubMed2004

Ultrasensitive electrical biosensing of proteins and DNA: carbon-nanotube derived amplification of the recognition and transduction events.

A new strategy for dramatically amplifying enzyme-linked electrical detection of proteins and DNA using carbon nanotubes (CNTs) for carrying numerous enzyme tracers and accumulating the enzymatically liberated product on CNT-modified transducer is described. Such a CNT-derived double-step amplification pathway (of both the recognition and transduction events) allows the detection of DNA and proteins down to 1.3 and 160 zmol, respectively, in 25-50 muL samples and indicates great promise for PCR-free DNA analysis. The new protocol is illustrated for monitoring sandwich hybridization and antibody-antigen interactions in connection with alkaline-phosphatase tracers. The DNA-linking of CNTs and particles holds promise also for assembling hybrid nanostructures relevant to molecular electronic devices.

Alkaline Phosphatase↗
PubMed2004

Capillary electrophoresis microchip with a carbon nanotube-modified electrochemical detector.

Significant improvements in the performance of a capillary electrophoresis (CE) microchip with an electrochemical detector are observed using a carbon nanotube (CNT)-modified working electrode. The CNT-modified electrode allows CE amperometric detection at significantly lower operating potentials and yields substantially enhanced signal-to-noise characteristics. The electrocatalytic detection is coupled to resistance to surface fouling and hence enhanced stability. Such advantages are illustrated in connection with several classes of hydrazine, phenol, purine, and amino acid compounds. Substantial minimization of surface fouling effects has been demonstrated in connection with the monitoring of phenol and tyrosine. Factors affecting the performance of the new CNT detector were assessed and optimized. CNTs from different sources are evaluated, and the effect of an anodic pretreatment is explored. The broad and significant catalytic activity exhibited by CNT-based CE detectors indicates great promise for a wide range of bioanalytical and environmental applications.

Journal Article↗
PubMed2004

Microchip capillary electrophoresis with a boron-doped diamond electrode for rapid separation and detection of purines.

Microchip capillary electrophoresis (CE) coupled with a boron-doped diamond (BDD) electrode has been employed for the separation and detection of several purines and purine-containing compounds. The BDD end-channel amperometric detector offers favorable signal-to-noise (S/N) characteristics at the high detection potential (+ 1.3 V) essential for detecting purine-related compounds. Factors influencing the separation and detection processes were examined and optimized. Five purines (guanine, hypoxanthine, guanosine, xanthine, and uric acid) have been separated within 6 min at a separation voltage of 1000V using a borate/phosphate run buffer (pH 8.2). Linear calibration plots are observed for micromolar concentrations of the purine compounds. Good stability and reproducibility (R.S.D. < 5%) are obtained reflecting the minimal adsorption of purines at the BDD surface. Applicability for the detection of nucleosides, nucleotides, and oligonucleotides is illustrated. The new microchip protocol offers great promise for a wide range of bioanalytical applications involving assays of purines and purine-containing compounds.

Diamond↗
PubMed2004

Vapor and liquid phase detection of cyanide on a microchip.

A capillary electrophoresis microchip is used to selectively and sensitively monitor cyanide levels in both vapor (HCN((g))) and aqueous (NaCN in drinking water) phases. Laser-induced fluorescence detection is applied using a violet diode laser to monitor the fluorescent isoindole derivative formed by the reaction of cyanide with 2,3-naphthalenedicarboxaldehyde (NDA) and taurine. Air sampling of hydrogen cyanide is achieved using a miniature impinger (2 mL), giving collection efficiencies as high as 79% for a sampling rate of 1.0 L/min and a 10 s sampling time (relative standard deviation RSD: 2.7% for n = 5). Following the addition of NDA and taurine to either the vapor phase impinger sample or an aqueous drinking water sample, the NDA/cyanide derivative can be detected in just over 40 s on the microchip, giving a detection limit of 0.56 microg/L and a linear dynamic range from 0.56 microg/L-2.4 mg/L. The detection limit for hydrogen cyanide in air was determined to be 2.3 ppb (mole%). On-chip derivatization of cyanide by NDA was successful, although a 50% decrease in signal intensity was observed due to insufficient time for completion of the reaction on the microchip. A number of different interferents were examined, and only iron(II) and chlorine showed any interference due to their capability for masking the presence of cyanide by reacting with free cyanide in solution.

Air Pollution↗
PubMed2004

Microchip capillary electrophoresis with a boron-doped diamond electrochemical detector for analysis of aromatic amines.

The attractive features of a boron-doped diamond (BDD) thin-film detector for microchip capillary electrophoretic (CE) separations of dye-related amino-substituted aromatic compounds are described. The diamond electrode was employed in the end-column amperometric detection of 4-aminophenol (4-AP), 1,2-phenylenediamine (1,2-PDA), 2-aminonaphthalene (2-AN), 2-chloroaniline (2-CA), and o-aminobenzoic acid (o-ABA), and its attractive behavior was compared to commonly used screen-printed carbon and glassy-carbon electrodes. These conventional electrode materials exhibit a significant degree of passivation and low sensitivity to the above-mentioned environmental pollutants. The diamond-based electrochemical detection system displayed a favorable analytical performance, including lower noise levels, higher peak resolution with enhanced sensitivity, and improved resistance against electrode passivation. Factors influencing the on-chip analysis were assessed and optimized. The diamond detector displayed detection limits of 2.0 and 1.3 microM for 4-AP and 2-AN, respectively, and a wide linear response for these compounds over the 2-50 microM range. The enhanced stability was demonstrated by relative standard deviation (RSD) values of 1.4% and 4.7% for 100 microM 1,2-PDA and 200 microM 2-CA, respectively, for repetitive detections (n = 7). Besides, the simultaneously observed current decrease was 2.4 and 9.1% for 1,2-PDA and 2-CA, respectively (compared to 21.8 and 41.0% at the screen-printed carbon electrode and 28.3 and 34.1% at the glassy carbon electrode, respectively). The favorable properties of the diamond electrode indicate great promise for environmental applications in CE and other microchip devices.

Amines↗
PubMed2003

Carbon nanotube screen-printed electrochemical sensors.

The fabrication, and evaluation of carbon-nanotube (CNT)-derived screen-printed (SP) electrochemical sensors based on a CNT ink are reported. The fabricated CNT strips combine the attractive advantages of CNT materials and disposable screen-printed electrodes. Such thick-film CNT sensors have a well-defined appearance, are mechanically stable, and exhibit high electrochemical reactivity.

Biosensing Techniques↗
PubMed2003

Carbon nanotube fiber microelectrodes.

Carbon nanotube (CNT) fibers have been used to fabricate microelectrodes with an attractive electrochemical behavior. By combining the advantages of CNT materials and fiber microelectrodes, the new material expands the scope of CNT-based electrochemical devices. The CNT fiber offers a marked decrease in the overvoltage for the NADH, dopamine, and hydrogen peroxide and circumvents NADH surface fouling effects. Heat treatment is shown to be extremely useful for activating the CNT fiber surfaces for electron transfer. SEM imaging and cyclic-voltammetric data indicate that the heat treatment leads to the removal of nonconducting residues and exposure of a "fresh" CNT surface. The new electrode material thus presents new opportunities for a wide range of electrochemical and analytical applications.

Journal Article↗