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Biomedical subjects

Joseph Wang

Publications and source records attributed to Joseph Wang.

At least 19 recordsLinked to original sources
PubMed2007

Sandwich electrochemical immunoassay for the detection of Staphylococcal enterotoxin B based on immobilized thiolated antibodies.

A new approach for the sensitive detection of Staphylococcal enterotoxin B (SEB) is presented based upon an electrochemical enzymatic immunoassay that utilizes thiolated antibodies immobilized on a gold surface. This method relies on the use of amine- or sulfhydryl-reactive heterobifunctional cross-linkers for the introduction of 2-pyridyl-disulfide groups to the antibody. The disulfide-containing linkages are subsequently cleaved with a suitable reducing agent, such as dithiothreitol (DTT), and the thiolated antibody-gold bond is covalently formed on a gold working electrode. Various cross-linking agents for immobilization of the capture antibody onto the gold electrode were investigated and compared. Factors influencing the thiolation and immobilization were investigated and optimized. The feasibility of such antibody immobilization and the subsequent sandwich enzyme immunoassay is demonstrated for the sensitive detection of SEB. The detection limit estimated from a representative dose-response curve is 1 ng/mL, corresponding to 5 pg in a 5-microL sample. Coupling the specificity of immunoassays with the sensitivity and low detection limits of electrochemical detection shows real promise for future sensing technology in enabling the development of single-use disposable devices.

Antibodies↗
PubMed2007

Carbon nanotube/poly(methyl methacrylate) (CNT/PMMA) composite electrode fabricated by in situ polymerization for microchip capillary electrophoresis.

We describe the development and application of a novel carbon nanotube/poly(methyl methacrylate) (CNT/PMMA) composite electrode as a sensitive amperometric detector of microchip capillary electrophoresis (CE). The composite electrode was fabricated by the in situ polymerization of a mixture of CNTs and prepolymerized methyl methacrylate in the microchannel of a piece of fused silica capillary under heat. The performance of this unique system was demonstrated by the separation and detection of phenolic pollutants and purines. The new CNT-based CE detector offered significantly lower operating potentials, yielded substantially enhanced signal-to-noise characteristics, and exhibited resistance to surface fouling and, hence, enhanced stability. Long-term stability and reproducibility with relative standard deviations of less than 5 % for the peak current (n=20) were also demonstrated. The simplicity and significant performance exhibited by the CNT/PMMA composite electrode indicate great promise for conventional CE, flowing-injection analysis, and other microfluidic analysis systems.

Electrochemistry↗
PubMed2006

Potentiometric biosensing of proteins with ultrasensitive ion-selective microelectrodes and nanoparticle labels.

We report here for the first time on the use of potentiometry for ultrasensitive nanoparticle-based detection of protein interactions. A silver ion-selective microelectrode is used to detect silver ions oxidatively released from silver enlarged gold nanoparticle labels in a sandwich immunoassay. Since potentiometry is expected to largely maintain its analytical characteristics upon reducing the sample volume, it is anticipated that this approach may form the basis for bioassays with attractive detection limits.

Biosensing Techniques↗
PubMed2006

Highly sensitive electrochemical detection of trace liquid peroxide explosives at a Prussian-blue 'artificial-peroxidase' modified electrode.

A highly sensitive electrochemical assay of the peroxide-based explosives triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD) at a Prussian-blue (PB) modified electrode is reported. The method involves photochemical degradation of the peroxide explosives and a low potential (0.0 V) electrocatalytic amperometric sensing of the generated hydrogen peroxide at the PB transducer and offers nanomolar detection limits following a short (15 s) irradiation times. The electrochemical sensing protocol should facilitate rapid field screening of peroxide explosives.

Bridged Bicyclo Compounds, Heterocyclic↗
PubMed2006

Acid stability of carbon paste enzyme electrodes.

This note reports on the unusual protection of several enzymes against harsh pH conditions provided by carbon paste electrodes. Both glucose oxidase and polyphenol oxidase carbon paste amperometric biosensors display a remarkable resistance to acid deactivation compared to conventional biosensors prepared by electropolymeric entrapment of enzymes. For example, the carbon paste enzyme electrodes fully retain their activity upon stressing in strongly acidic conditions (pH approximately 2.0-2.5) for prolonged periods, where conventional (polymer-based) biosensors rapidly lose most of their response. Such unusual acid stability of carbon paste enzyme electrodes is attributed to the "pH memory" of enzymes in the hydrophobic paste environment, to the barrier to hydronium ions provided by the pasting liquid and to decreased conformational mobility.

Acids↗
PubMed2006

Nanoparticle-based sensing of glycan-lectin interactions.

Here we present the first report on nanoparticle-based biosensing of glycan markers of diseases. The protocol relies on the competition between a nanocrystal (CdS)-tagged sugar and the target sugar for the binding sites of surface-confined lectin and monitoring the extent of competition through highly sensitive electrochemical detection of the captured nanocrystal. This development is expected to allow decentralized detection of carbohydrate moieties and lectin-carbohydrate interactions to be performed more rapidly, sensitively, inexpensively, and reliably.

Lectins↗
PubMed2006

Electrochemical detection of E. coli 16S rDNA sequence using air-plasma-activated fullerene-impregnated screen printed electrodes.

A new DNA modified electrode for the electrochemical detection of 16S rDNA extracted from Escherichia coli (JCM1649) is proposed. The electrodes were fabricated by screen printing a fullerene-impregnated carbon ink onto a poly(methylmethacrylate) substrate and immobilizing a probe DNA on the surface after activating the electrode with air plasma. The results indicated a dramatic improvement in the surface coverage of the immobilized probe DNA, and of the reduction peak of the redox indicator (Co(phen)(3)(3+)) due to the incorporation of fullerene. By immobilizing the probe onto the fullerene-impregnated screen-printed electrodes, the PCR product of the 16S rDNA extracted from E. coli was directly detected without any pretreatment. A well defined signal difference was observed between the perfectly matching oligonucleotide and the mismatching one, and it was possible to detect the target at the modified electrode. This method enabled us to clearly detect the two base mismatches in the ca. 1500-bases long 16S rDNA sequence.

Air↗
PubMed2006

Sensitive and rapid electrochemical bioassay of glycosidase activity.

Here we present a highly sensitive, rapid and simple electrochemical assay for glycosidases based on treatment of the glycosidase with the appropriate p-nitrophenyl glycoside and anodic detection of released p-nitrophenol. The attractive characteristics of the new bioassay should facilitate advanced glycomic research and routine clinical diagnostics since glycosidases are associated with various diseases.

Bacteria↗
PubMed2006

Magnetic tuning of the electrochemical reactivity through controlled surface orientation of catalytic nanowires.

Nanowires have received considerable attention owing to their broad potential applications. We report here on the application of nanowires for magnetic control of the electrochemical reactivity and demonstrate how one can modulate the electrocatalytic activity by orienting catalytic nanowires at different angles. Unlike early "on/off" magnetic switching studies based on functionalized magnetic spheres, the present magnetoswitchable protocol relies on modulating the electrochemical reactivity without removing the magnetic material from the surface. Such behavior is attributed to the reversible blocking of the redox processes and to changes in the tortuosity-dependent flux rate. The nanowire-based magnetoswitchable protocol may be extremely useful for adjusting the electrochemical reactivity, such as for tuning the power output of fuel cells (rather than switching the power on/off).

Journal Article↗
PubMed2006

Templated one-step synthesis of compositionally encoded nanowire tags.

Multimetal nanowire tags, with distinct encoding patterns, have been prepared using a one-step templated electrodeposition from solutions containing different concentrations of various metal ions. Such synthesis of compositionally encoded nanowire tags is substantially faster and simpler than the preparation of striped nanowires based on sequential plating steps from different metal solutions and leads to high identification accuracy. The alloy nanowire preparation route leads to a high coding capacity with a large number of distinguishable voltammetric signatures, reflecting the predetermined composition of the metal mixture plating solution (and hence the nanowire composition). Factors influencing the identification accuracy are evaluated using three-metal (In, Pb, Bi) alloy nanowires, and the relative advantages and disadvantages of the new route are discussed.

Alloys↗
PubMed2006

Nanoparticle-based assays of antioxidant activity.

The antioxidant power of several phenolic acids and related food samples is estimated from the generation and growth of gold nanoparticles. The intensity of the resulting particle plasmon absorption bands correlates well with the redox characteristics of these phenolic acids estimated from cyclic voltammetry experiments. The highest capacity of reducing gold(III) to gold nanoparticles corresponds to the highest antioxidant activity, consistent with the tendency of phenolic acids to donate electrons.

Antioxidants↗
PubMed2006

Quantum-dot/aptamer-based ultrasensitive multi-analyte electrochemical biosensor.

The coupling of aptamers with the coding and amplification features of inorganic nanocrystals is shown for the first time to offer a highly sensitive and selective simultaneous bioelectronic detection of several protein targets. This is accomplished in a single-step displacement assay in connection to a self-assembled monolayer of several thiolated aptamers conjugated to proteins carrying different inorganic nanocrystals. Electrochemical stripping detection of the nondisplaced nanocrystal tracers results in a remarkably low (attomole) detection limit, that is, significantly lower than those of existing aptamer biosensors. The new device offers great promise for measuring a large panel of disease markers present at ultralow levels during early stages of the disease progress.

Aptamers, Peptide↗
PubMed2006

Point-of-care biosensor systems for cancer diagnostics/prognostics.

With the growing number of fatalities resulting from the 100 or so cancer-related diseases, new enabling tools are required to provide extensive molecular profiles of patients to guide the clinician in making viable diagnosis and prognosis. Unfortunately with cancer-related diseases, there is not one molecular marker that can provide sufficient information to assist the clinician in making effective prognoses or even diagnoses. Indeed, large panels of markers must typically be evaluated that cut across several different classes (mutations in certain gene fragments--DNA; over/under-expression of gene activity as monitored by messenger RNAs; the amount of proteins present in serum or circulating tumor cells). The classical biosensor format (dipstick approach for monitoring the presence of a single element) is viewed as a valuable tool in many bioassays, but possesses numerous limitations in cancer due primarily to the single element nature of these sensing platforms. As such, if biosensors are to become valuable tools in the arsenal of the clinician to manage cancer patients, new formats are required. This review seeks to provide an overview of the current thinking on molecular profiling for diagnosis and prognosis of cancers and also, provide insight into the current state-of-the-art in the biosensor field and new strategies that must be considered to bring this important technology into the cancer field.

Biomarkers, Tumor↗
PubMed2006

V-type nerve agent detection using a carbon nanotube-based amperometric enzyme electrode.

An enzyme electrode for the detection of V-type nerve agents, VX (O-ethyl-S-2-diisopropylaminoethyl methylphosphonothioate) and R-VX (O-isobutyl-S-2-diethylaminoethyl methylphosphonothioate), is proposed. The principle of the new biosensor is based on the enzyme-catalyzed hydrolysis of the nerve agents and amperometric detection of the thiol-containing hydrolysis products at carbon nanotube-modified screen-printed electrodes. Demeton-S was used as a nerve agent mimic. 2-(Diethylamino)ethanethiol (DEAET) and 2-(dimethylamino)ethanethiol (DMAET), the thiol-containing hydrolysis product and hydrolysis product mimic of R-VX and VX, respectively, were monitored by exploiting the electrocatalytic activity of carbon nanotubes (CNT). As low as 2 microM DMAET and 0.8 microM DEAET were detected selectively at a low applied potential of 0.5 V vs Ag/AgCl at a CNT-modified mediator-free amperometric electrode. Further, the large surface area and the hydrophobicity of CNT was used to immobilize organophosphorus hydrolase mutant with improved catalytic activity for the hydrolysis of the P-S bond of phosphothiolester neurotoxins including VX and R-VX nerve gases to develop a novel, mediator-free, membrane-free biosensor for V-type nerve agents. The applicability of the biosensor was demonstrated for direct, rapid, and selective detection of V-type nerve agents' mimic demeton-S. The selectivity of the sensor against interferences and application to spiked lake water samples was demonstrated.

Biosensing Techniques↗
PubMed2006

Biocatalytically induced formation of cupric ferrocyanide nanoparticles and their application for electrochemical and optical biosensing of glucose.

The enzymatically controlled growth of cupric ferrocyanide nanoparticles in the presence of glucose oxidase, its ferricyanide electron acceptor, and copper ions is described. The biocatalytically stimulated growth of these nanoparticles on the surface of carbon-paste electrodes results in an amplified electrochemical detection of the glucose substrate. This concept can readily be expanded for monitoring a wide range of biocatalytic processes involving the ferricyanide electron acceptor.

Biopolymers↗
PubMed2005

Electrochemical biosensors: towards point-of-care cancer diagnostics.

Wide-scale point-of-care diagnostic systems hold great promise for early detection of cancer at a curable stage of the disease. This review discusses the prospects and challenges of electrochemical biosensors for next-generation cancer diagnostics. Electrochemical biosensors have played an important significant role in the transition towards point-of-care diagnostic devices. Such electrical devices are extremely useful for delivering the diagnostic information in a fast, simple, and low cost fashion in connection to compact (hand-held) analyzers. Modern electrochemical bioaffinity sensors, such as DNA- or immunosensors, offer remarkable sensitivity essential for early cancer detection. The coupling of electrochemical devices with nanoscale materials offers a unique multiplexing capability for simultaneous measurements of multiple cancer markers. The attractive properties of electrochemical devices are extremely promising for improving the efficiency of cancer diagnostics and therapy monitoring. With further development and resources, such portable devices are expected to speed up the diagnosis of cancer, making analytical results available at patient bedside or physician office within few minutes.

Biomarkers, Tumor↗