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Biomedical subjects

Joseph Wang

Publications and source records attributed to Joseph Wang.

At least 37 records · Page 2Linked to original sources
PubMed2005

Fabrication of poly(methyl methacrylate) capillary electrophoresis microchips by in situ surface polymerization.

A novel method based on in situ surface polymerization of methyl methacrylate (MMA) has been developed for the rapid fabrication of poly(methyl methacrylate) (PMMA) capillary electrophoresis (CE) microchips. MMA containing both thermal and ultraviolet (UV) initiators was allowed to prepolymerize in a water bath to form a fast curing molding solution that was subsequently sandwiched between a nickel template and a PMMA plate. The images of the raised microchannels on the nickel template were precisely replicated into the synthesized PMMA substrates during the UV-initiated polymerization of the molding solution within 30 min under ambient temperature. The attractive performances of the novel PMMA microchips have been demonstrated in connection with amperometric detection for the separation and detection of several model analytes. The new approach significantly simplifies the process for fabricating PMMA devices and could be applied to other materials that undergo light-initiated polymerization.

Electrophoresis, Capillary↗
PubMed2005

Highly sensitive and selective amperometric microbial biosensor for direct determination of p-nitrophenyl-substituted organophosphate nerve agents.

We report herein a whole cell-based amperometric biosensor for highly selective, highly sensitive, direct, single-step, rapid, and cost-effective determination of organophosphate pesticides with a p-nitrophenyl substituent. The biosensor was comprised of a p-nitrophenol degrader, Pseudomonas putida JS444, genetically engineered to express organophosphorus hydrolase (OPH) on the cell surface immobilized on the carbon paste electrode. Surface-expressed OPH catalyzed hydrolysis of the p-nitrophenyl substituent organophosphorus pesticides such as paraoxon, parathion, and methyl parathion to release p-nitrophenol, which was subsequently degraded by the enzymatic machinery of P. putida JS444. The electrooxidization 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 0.086 mg dry weight of cells operating at 600 mV applied potential (vs Ag/AgCl reference) in 50 mM citrate--phosphate pH 7.5 buffer with 50 microM CoCl2 at room temperature. Under optimum operating conditions the biosensor measured as low as 0.28 ppb of paraoxon, 0.26 ppb of methyl parathion, and 0.29 ppb parathion. These detection limits are comparable to cholinesterase inhibition-based biosensors. Unlike the inhibition-based format, this biosensor manifests a selective response to organophosphate pesticides with a p-nitrophenyl substituent only, has a simplified single-step protocol with short response time, and can be used for repetitive/multiple and on-line analysis. The service life of the microbial amperometric biosensor was 5 days when stored in the operating buffer at 4 degrees C. The new biosensor offers great promise for rapid environmental monitoring of OP pesticides with nitrophenyl substituent.

Aryldialkylphosphatase↗
PubMed2005

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

This article describes an effective microchip capillary-electrophoresis protocol for rapid and effective measurements of food-related seleno amino acids, including Se-methionine (Se-Met), Se-ethionine (Se-Eth), Se-methyl cysteine (Se-Cys), utilizing o-phtaldialdeyde/2-mercaptoethanol (OPA/2-ME) derivatization. Relevant parameters of the chip separation and amperometric detection are examined and optimized using a response surface methodology (RSM). Under optimum conditions, the analytes could be separated and detected in a 30 mM borate buffer (pH 9.3, with 28 mM sodium dodecul sulfate) within 300 s using a separation voltage of 2000V and a detection voltage of +0.9 V. Linear calibration plots are observed for micromolar concentrations of the Se-amino acid compounds. The negligible sample volumes used in the microchip procedure obviates surface fouling common to amperometric measurements of selenoamino-acid compounds. The new microchip protocol offers great promise for a wide range of food applications requiring fast measurements and negligible sample consumption.

Amino Acids↗
PubMed2005

Continuous monitoring with microfabricated capillary electrophoresis chip devices.

We report on the direct coupling of hydrodynamically flowing stream to a microchip capillary electrophoresis (CE) for continuous assays of liquid samples. The new interface relies on mounting the sample tubing onto a sharp inlet tip and allows rapid, convenient and reproducible electrokinetic loading from a continuously flowing stream directly into the narrow separation microchannel. The sharp inlet interface is characterized by its efficiency, stability and simplicity. The effect of the sample flow rate, applied voltages and other relevant variables, is described. It was found that the peak intensity is independent of the flow rate. The performance of the new interface is illustrated for on-line CE-electrochemical monitoring of phenolic and explosive compounds. Conditions simulating continuous long-term monitoring, led to a highly stable response for a 15 ppm 1,3,5-trinitrobenzene solution (RSD = 3.7%, n= 40). Such ability to continuously introduce flowing samples into micrometer channels makes 'lab-on-a-chip' devices highly compatible with real-life monitoring applications.

Electrophoresis, Microchip↗
PubMed2005

DNA hybridization detection at heated electrodes.

The detection of DNA hybridization is of central importance to the diagnosis and treatment of genetic diseases. Due to cost limitations, small and easy-to-handle testing devices are required. Electrochemical detection is a promising alternative to evaluation of chip data with optical readout. Independent of the actual readout principle, the hybridization process still takes a lot of time, hampering daily use of these techniques, especially in hospitals or doctor's surgery. Here we describe how direct local electrical heating of a DNA-probe-modified gold electrode affects the surface hybridization process dramatically. We obtained a 140-fold increase of alternating current voltammetric signals for 20-base ferrocene-labeled target strands when elevating the electrode temperature during hybridization from 3 to 48 degrees C while leaving the bulk electrolyte at 3 degrees C. At optimum conditions, a target concentration of 500 pmol/L could be detected. Electrothermal regeneration of the immobilized DNA-probe strands allowed repetitive use of the same probe-modified electrode. The surface coverage of DNA probes, monitored by chronocoulometry of hexaammineruthenium(III), was almost constant upon heating to 70 degrees C. However, the hybridization ability of the probe self-assembled monolayer declined irreversibly when using a 70 degrees C hybridization temperature. Coupling of heated electrodes and highly sensitive electrochemical DNA hybridization detection methods should enhance detection limits of the latter significantly.

DNA↗
PubMed2005

Nanostructured polyamic acid membranes as novel electrode materials.

This paper describes a new approach for the preparation of polyamic acid (PAA) composites containing Ag and Au nanoparticles. The composite film of PAA and metal particles were obtained upon electrodeposition of a PAA solution containing gold or silver salts with subsequent thermal treatment, while imidization to polyimide is prevented. The structural characterization of the films is provided by 1H NMR and Fourier transform infrared spectroscopy (FTIR), while the presence of metallic nanoparticles within the polymeric matrix was confirmed by scanning electron microscopy (SEM), cyclic voltammetry (CV), energy-dispersive X-ray analysis (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). This approach utilizes the unique reactivity of PAA by preventing the cyclization of the reactive soluble intermediate into polyimides at low temperature to design polymer-assisted nanostructured materials. The ability to prevent the cyclization process should enable the design of a new class of electrode materials by use of thermal reduction and/or electrodeposition.

Benzene Derivatives↗
PubMed2005

Multiple enzyme layers on carbon nanotubes for electrochemical detection down to 80 DNA copies.

Signal amplification using enzyme multilayers on carbon nanotube (CNT) templates is shown to yield a remarkably sensitive electrochemical detection of proteins and nucleic acids. The electrostatic layer-by-layer (LBL) self-assembly onto CNT carriers maximizes the ratio of enzyme tags per binding event to offer the greatest amplification factor reported to date. Absorption spectroscopy, TEM, and electrochemical characterization confirm the formation of LBL enzyme nanostructures on individual CNT carriers. The enzymatic activity is found to increase with the number of enzyme layers. The new protocol is illustrated for monitoring sandwich hybridization and antibody-antigen interactions in connection with alkaline phosphatase tracers. Factors affecting the enzyme loading and the analytical performance have been optimized. Such amplified bioelectronic assays allow detection of DNA and proteins down to 80 copies (5.4 aM) and 2000 protein molecules (67 aM), respectively. Given the enormous amplification afforded by the new CNT-LBL biolabel, such route offers great promise for ultrasensitive detection of infectious agents and disease markers.

DNA↗
PubMed2005

Enzyme nanoparticles-based electronic biosensor.

A simple and effective method to prepare an enzyme electronic biosensor by immobilizing enzyme nanoparticles directly onto the gold electrode surface is described; prepared horseradish peroxidase nanoparticles have been successfully used to develop reagentless electronic biosensors for H2O2 detection without promoters and mediators and offer great potential to develop enzyme-based electronic biosensors.

Biosensing Techniques↗
PubMed2005

Nanocrystal-based bioelectronic coding of single nucleotide polymorphisms.

A bioelectronic method for coding unknown single nucleotide polymorphisms (SNPs) based on the use of different encoding nanocrystals is described. Four such nanocrystals, ZnS, CdS, PbS, and CuS, linked to the adenosine, cytidine, guanosine and thymidine mononucleotides, respectively, are sequentially introduced to the DNA hybrid-coated magnetic-bead solution. Each mutation captures via base pairing different nanocrystal-mononucleotide conjugates, and yields a characteristic multipotential voltammogram, whose peak potentials reflect the identity of the mismatch. The mismatch recognition events are being amplified by the metal accumulation feature of the stripping voltammetric transduction mode. Each of the eight possible one-base mismatches can thus be identified in a single voltammetric run. The use of nanocrystal tracers for detecting two known mutations in a single DNA target is also illustrated in connection to nanocrystals linked to two nucleotides along with a single voltammetric run. The protocol presented should facilitate the rapid, simple, low-cost, and high throughput screening for SNPs.

Base Pair Mismatch↗
PubMed2005

Carbon nanotube--conducting-polymer composite nanowires.

Polypyrrole/carbon nanotube (PPy/CNT) composite nanowires were prepared by a template-directed electrochemical synthetic route, involving plating of PPy into the pores of a host membrane in the presence of shortened and carboxylated CNT dopants (without added electrolyte). Cyclic voltammetric growth profiles indicate that the CNT is incorporated within the growing nanowire and serves as the sole charge-balancing "counterion". Transmission electron microscopy images indicate high-quality straight PPy/CNT nanowires with a smooth and featureless surface and a uniform diameter. The presence of the CNT dopant imparts high conductivity (Ohmic I-V behavior) onto these PPy/CNT nanowires. By combining the attractive properties of CNTs, conducting polymers, and nanowires, the new nanocomposite opens up new opportunities, ranging from chemical sensors to molecular electronic devices.

Journal Article↗
PubMed2005

Carbon nanotubes (CNTs) for the development of electrochemical biosensors.

Carbon nanotube (CNT) is a very attractive material for the development of biosensors because of its capability to provide strong electrocatalytic activity and minimize surface fouling of the sensors. This article reviews our recent developments of oxidase- and dehydrogenase-amperometric biosensors based on the immobilization of CNTs, the co-immobilization of enzymes on the CNTs/Nafion or the CNT/Teflon composite materials, or the attachment of enzymes on the controlled-density aligned CNT-nanoelectrode arrays. The excellent electrocatalytic activities of the CNTs on the redox reactions of hydrogen peroxide, nicotinamide adenine dinucleotide (NADH), and homocysteine have been demonstrated. Successful applications of the CNT-based biosensors reviewed herein include the low-potential detections of glucose, organophosphorus compounds, and alcohol.

Alcohols↗
PubMed2005

Nanomaterial-based amplified transduction of biomolecular interactions.

This article reviews progress in the development of nanomaterials for amplified biosensing and discusses different nanomaterial-based bioamplification strategies. Signal amplification has attracted considerable attention for ultrasensitive detection of disease markers and biothreat agents. The emergence of nanotechnology is opening new horizons for highly sensitive bioaffinity and biocatalytic assays and for novel biosensor protocols that employ electronic, optical, or microgravimetric signal transduction. Nucleic acids and antibodies functionalized with metal or semiconductor nanoparticles have been employed as amplifying tags for the detection of DNA and proteins. The coupling of different nanomaterial-based amplification platforms and amplification processes dramatically enhances the intensity of the analytical signal and leads to ultrasensitive bioassays. The successful realization of the new nanoparticle-based signal amplification strategies requires proper attention to nonspecific adsorption issues. The implications of such nanoscale materials on amplified biodetection protocols and on the development of modern biosensors are discussed.

Adsorption↗
PubMed2005

An electrochemical RNA hybridization assay for detection of the fecal indicator bacterium Escherichia coli.

Monitoring waters for indicator bacteria is required to protect the public from exposure to fecal pollution. Our proof-of-concept study describes a method for detecting fecal coliforms. The coliform Escherichia coli was used as a model fecal indicator. DNA probe-coated magnetic beads in combination with the electrochemical monitoring of the oxidation state of guanine nucleotides should allow for direct detection of bacterial RNA. To demonstrate this concept, we used voltammetry in connection with pencil electrodes to detect isolated E. coli 16S rRNA. Using this approach, 10(7) cells of E. coli were detected in a quantitative, reproducible fashion in 4h. Detection was achieved without a nucleic acid amplification step. The specificity of the assay for coliforms was demonstrated by testing against a panel of bacterial RNA. We also show that E. coli RNA can be detected directly from cell extracts. The method could be used for on-site detection and shows promise for adaptation into automated biosensors for water-quality monitoring.

Biological Assay↗
PubMed2005

Nanomaterial-based electrochemical biosensors.

The unique properties of nanoscale materials offer excellent prospects for interfacing biological recognition events with electronic signal transduction and for designing a new generation of bioelectronic devices exhibiting novel functions. In this Highlight I address recent research that has led to powerful nanomaterial-based electrical biosensing devices and examine future prospects and challenges. New nanoparticle-based signal amplification and coding strategies for bioaffinity assays are discussed, along with carbon-nanotube molecular wires for achieving efficient electrical communication with redox enzyme and nanowire-based label-free DNA sensors.

Biosensing Techniques↗
PubMed2004

Electrochemical coding for multiplexed immunoassays of proteins.

An electrochemical immunoassay protocol for the simultaneous measurements of proteins, based on the use of different inorganic nanocrystal tracers is described. The multiprotein electrical detection capability is coupled to the amplification feature of electrochemical stripping transduction (to yield fmol detection limits) and with an efficient magnetic separation (to minimize nonspecific adsorption effects). The multianalyte electrical sandwich immunoassay involves a dual binding event, based on antibodies linked to the nanocrystal tags and magnetic beads. Carbamate linkage is used for conjugating the hydroxyl-terminated nanocrystals with the secondary antibodies. Each biorecognition event yields a distinct voltammetric peak, whose position and size reflects the identity and level, respectively, of the corresponding antigen. The concept is demonstrated for a simultaneous immunoassay of beta(2)-microglobulin, IgG, bovine serum albumin, and C-reactive protein in connection with ZnS, CdS, PbS, and CuS colloidal crystals, respectively. These nanocrystal labels exhibit similar sensitivity. Such electrochemical coding could be readily multiplexed and scaled up in multiwell microtiter plates to allow simultaneous parallel detection of numerous proteins or samples and is expected to open new opportunities for protein diagnostics and biosecurity.

Animals↗
PubMed2004

Bulk modification of polymeric microfluidic devices.

The surface properties of microfluidic devices play an important role in their flow behavior. We report here on an effective control of the surface chemistry and performance of polymeric microchips through a bulk modification route during the fabrication process. The new protocol is based on modification of the bulk microchip material by tailored copolymerization of monomers during atmospheric-pressure molding. A judicious addition of a modifier to the primary monomer solution thus imparts attractive properties to the plastic microchip substrate, including significant enhancement and/or modulation of the EOF (with flow velocities comparable to those of glass), a strong pH sensitivity and high stability. Carboxy, sulfo, and amino moieties have thus been introduced (through the incorporation of methylacrylic acid, 2-sulfoethyl-methacrylate and 2-aminoethyl-methacrylate monomers, respectively). A strong increase in the electroosmotic pumping compared to the native poly(methylmethacrylate)(PMMA) microchip (ca. electroosmotic mobility increases from 2.12 to 4.30 x 10(-4) cm(2) V(-1) s(-1)) is observed using a 6% methylacrylate (MAA) modified PMMA microchip. A 3% aminoethyl modified PMMA microchip exhibits a reversal of the electroosmotic mobility (for example, -5.6 x 10(-4) cm(2) V(-1) s(-1) at pH 3.0). The effects of the modifier loading and the pH on the EOF have been investigated for the MAA-modified PMMA chips. The bulk-modified devices exhibit reproducible and stable EOF behavior. The one step fabrication/modification protocol should further facilitate the widespread production of high-performance plastic microchip devices.

Journal Article↗