Glycan array on aluminum oxide-coated glass slides through phosphonate chemistry

A new type of glycan array covalently or noncovalently attached to aluminum oxide-coated glass (ACG) slides has been developed for studies of enzymatic reactions and protein binding. To prepare the noncovalent array, glycans with a polyfluorinated hydrocarbon (-C(8)F(17)) tail are spotted robotically onto the ACG slide surface containing a layer of polyfluorinated hydrocarbon terminated with phosphonate. After incubation and washing, the noncovalent array can be characterized by MS-TOF via ionization/desorption at a low laser energy without addition of matrix. A representative cellotetraose array was developed to study the activity and specificity of different cellulases and to differentiate the exo- and endoglucanase activities. To prepare the covalent array, glycans with a phosphonic acid tail were synthesized and spotted robotically onto the ACG slide surface. After incubation, the slides can be used directly for quantitative protein binding analysis. Compared to the preparation of glycan arrays on glass slides and other surfaces, this method of arraying using phosphonic acid reacting with ACG is more direct, convenient, and effective and represents a new platform for the high-throughput analysis of protein-glycan interactions.

Glycan arrays on aluminum-coated glass slides

We have developed a novel method of immobilizing glycans onto aluminum-coated glass (ACG) slides for potential use in disease diagnosis and drug discovery. The quality of these sugar chips can be assessed by mass spectrometry and fluorescence measurements with high sensitivity. The unique properties of ACG slides include: 1) the metal oxide layer on the surface can be activated for grafting organic compounds such as modified oligosaccharides; 2) the surface remains electrically conductive, and the grafted oligosaccharides can be simultaneously characterized by mass spectrometry and carbohydrate-binding assay; and 3) the slides are more sensitive than transparent glass slides in binding analysis. To demonstrate this, we synthesized a model compound of mannose with a built-in photocleavable linker bound to the ACG slide surface. The molecular weight of the grafted mannose was identified by mass spectrometry, and the slide was subjected to biotinylated ConA binding followed by Cy3-tagged streptavidin detection. This method was further extended to the preparation of glycan arrays containing lactose and the cancer antigen Globo H.

An homogeneous fluorescence polymerase chain reaction assay to identify Salmonella

We have developed a semiquantitative homogeneous fluorescence assay that combines polymerase chain reaction (PCR) amplification with direct fluorescence detection (HF-PCR). The assay eliminates the need to perform gel electrophoresis on test samples. Using a set of Salmonella-specific primers, this system was used to verify suspect colonies from culture plates as Salmonella. The fluorescence signal is generated by a nucleic acid dye, YO-PRO-1, that is included in the amplification reaction. This homogeneous PCR assay was used to test 84 Salmonella strains picked from selective culture plates. All data indicated positive results when compared with 17 non-Salmonella strains (in general, Citrobacter, Hafnia, Proteus, and Escherichia). The HF-PCR assay is a sensitive, simple, accurate, and reproducible method that correlates well with size-exclusion high-performance liquid chromatography and gel electrophoresis techniques as a means to monitor PCR-mediated DNA amplification. This assay can confirm suspect colonies within 2.5 h.

Aggregation and concentration-dependent sorting of exocrine regulated secretory proteins

Sorting between the regulated and the constitutive secretory pathway in exocrine cells is thought to involve aggregation of regulated secretory proteins. This study demonstrates that, unlike endocrine secretory proteins, exocrine secretory proteins, including amylase, do not undergo homotypic aggregation under the conditions found in the sorting organelles. Also, unlike other exocrine proteins, amylase does not aggregate with chondroitin sulfate. Since amylase exhibits heterotypic aggregation, the role of protein concentration in amylase sorting was tested in AR42J cells. Secretion was stimulated with substance P and cholecystokinin from both untreated and dexamethasone-treated cells, with more efficient stimulation from dexamethasone-treated cells. These results indicate that amylase sorting is enhanced when its expression is stimulated by dexamethasone treatment.

Source localization of averaged and single EEG spikes using the electric dipole model

A scheme for localizing the epileptic focus is proposed. The scheme is on the basis of a model with an electric dipole inside a four-layer inhomogeneous spherical model of head and utilizes a nonlinear programming algorithm applying the gradient projection method. Various initial estimates are used to prove the stability of the implemented dipole model. Fourteen single spike data and the averaged spike data are used to localize the epileptic focus. The results of the usage of the averaged spike data show that the dipole position is compatible with visual inspection of experienced clinical physicians. The results of the usage of the single spike show that 11 of the 14 single spikes have dipole locations near the result of the averaged spike but the estimated dipole moments differ markedly from one another. The localization results of the other three single spikes show that the dipole position is strongly affected by the background EEG. This kind of interference generally causes the eccentricity of the dipole to deviate from its anatomically meaningful value. According to our results, the electric dipole model is concluded to be valuable for the clinical application of localizing epileptic foci.

Evaluation of parametric methods in EEG signal analysis

In this paper, a well designed database, considering statistical characteristics and including all types of Electroencephalogram (EEG) is built. 900 EEG segments, each with a short interval (1.024 sec) in this database are clustered into eight classes. Three tests of white noise for evaluating the efficiency of autoregressive (AR) and autoregressive-moving average (ARMA) models are proposed. The Akaike information criterion (AIC) is used for determining orders of AR and ARMA models. The AR model requires a higher model order (8.67 on the average) than the ARMA model (6.17 on the average). However, it is found that about 96% of the 900 segments can be efficiently represented by the AR model, and only about 78% of them can be efficiently represented by ARMA model. We therefore conclude that the AR model is preferred for estimating EEG signals.

Sensitive, colorimetric enzyme amplification cascade for determination of alkaline phosphatase and application of the method to an immunoassay of thyrotropin

A highly sensitive flavin adenine dinucleotide-3'-phosphate (FADP)-based enzyme amplification cascade has been developed for determining alkaline phosphatase (ALP; EC 3.1.3.1). The cascade detects ALP via the dephosphorylation of the novel substrate FADP to produce the cofactor FAD, which binds stoichiometrically to inactive apo D-amino acid oxidase (D-AAO). The resulting active holo D-AAO oxidizes D-proline to produce hydrogen peroxide, which is quantified by the horseradish peroxidase-mediated conversion of 3,5-dichloro-2-hydroxybenzenesulfonic acid and 4-aminoantipyrine to a colored product. The FADP-based enzyme amplification cascade has been used in a novel releasable linker immunoassay (RELIA) to quantify thyrotropin (TSH). In the assay, TSH is first captured onto antibody-coated chromium dioxide particles. After formation of an antibody-TSH sandwich with a dethiobiotinylated second antibody, the complex is reacted with a streptavidin-ALP conjugate. Biotin is then used to release the conjugate into solution, and ALP is quantified in an automated version of the FADP-based amplification cascade on the aca discrete clinical analyzer (Du Pont). The sensitivity of the colorimetric RELIA assay for TSH (less than 0.1 milli-int. unit/L) is comparable with that of fluorometric assays. This technology provides a way to adapt to the aca high-sensitivity immunoassays for a wide range of analytes via colorimetric detection.

Sensitive, colorimetric enzyme amplification cascade for determination of alkaline phosphatase and application of the method to an immunoassay of thyrotropin

A highly sensitive flavin adenine dinucleotide-3'-phosphate (FADP)-based enzyme amplification cascade has been developed for determining alkaline phosphatase (ALP; EC 3.1.3.1). The cascade detects ALP via the dephosphorylation of the novel substrate FADP to produce the cofactor FAD, which binds stoichiometrically to inactive apo D-amino acid oxidase (D-AAO). The resulting active holo D-AAO oxidizes D-proline to produce hydrogen peroxide, which is quantified by the horseradish peroxidase-mediated conversion of 3,5-dichloro-2-hydroxybenzenesulfonic acid and 4-aminoantipyrine to a colored product. The FADP-based enzyme amplification cascade has been used in a novel releasable linker immunoassay (RELIA) to quantify thyrotropin (TSH). In the assay, TSH is first captured onto antibody-coated chromium dioxide particles. After formation of an antibody-TSH sandwich with a dethiobiotinylated second antibody, the complex is reacted with a streptavidin-ALP conjugate. Biotin is then used to release the conjugate into solution, and ALP is quantified in an automated version of the FADP-based amplification cascade on the aca discrete clinical analyzer (Du Pont). The sensitivity of the colorimetric RELIA assay for TSH (less than 0.1 milli-int. unit/L) is comparable with that of fluorometric assays. This technology provides a way to adapt to the aca high-sensitivity immunoassays for a wide range of analytes via colorimetric detection.

Enzyme-amplified rate conductimetric immunoassay

A new immunoassay technique based on measurement of conductance changes in solutions is described. The assay employs an immobilized monoclonal antibody to capture a protein analyte along with a second antibody to the same analyte, conjugated to an enzyme capable of producing ions which are measured conductimetrically. Urease was selected as the enzyme, because it produces, from urea, four ions for each catalytic event. The analyte studied was human chorionic gonadotropin in serum. Higher concentrations of analyte during incubation with immobilized antibody and antibody-urease conjugate led to increased binding of the latter. After removal of unbound conjugate, urea solution was added and the rate of conductance change measured in the bulk substrate solution. Experiments, performed in polystyrene microtiter wells using a specially designed electrode, demonstrated the ability to measure 30 picomolar concentrations of human chorionic gonadotropin with a 30-s rate measurement. Urease proved to be an excellent labeling enzyme, retaining its activity under the nonionic conditions necessary to maintain low background conductance. Good agreement was obtained between observed rates and those expected from conductimetric theory and known physical parameters. The potential utility of the conductimetric immunoassay lies in the fabrication of biosensor devices for simplification and cost reduction of immunochemical-based instrumentation. Further improvements to the technique are proposed to achieve lower detection limits.

Application of novel chromium dioxide magnetic particles to immunoassay development

We have used chromium dioxide magnetic particles as the solid support in developing a series of immunological tests. The high surface area (greater than 40 m2/g) available on the magnetic particles and their easy dispersion throughout a solution allow for rapid and complete capture of the target antigen. The magnetic responsiveness of the particles allows for rapid, high-efficiency washing to reduce nonspecific binding, which often limits the sensitivity of serological assays. These features form the basis of extremely rapid and flexible assays for several hormones and markers of cancer and infectious disease. Most of the assays involve monoclonal antibodies. Here we describe specific performance characteristics for thyroxin, follitropin, creatine kinase isoenzyme MB, and antibody to human immunodeficiency virus (HIV). All of the assays are performed in less than 90 min, many in 30 to 45 min. The technology is highly flexible and is suitable for a variety of formats, from manual to fully automated.

Application of novel chromium dioxide magnetic particles to immunoassay development

We have used chromium dioxide magnetic particles as the solid support in developing a series of immunological tests. The high surface area (greater than 40 m2/g) available on the magnetic particles and their easy dispersion throughout a solution allow for rapid and complete capture of the target antigen. The magnetic responsiveness of the particles allows for rapid, high-efficiency washing to reduce nonspecific binding, which often limits the sensitivity of serological assays. These features form the basis of extremely rapid and flexible assays for several hormones and markers of cancer and infectious disease. Most of the assays involve monoclonal antibodies. Here we describe specific performance characteristics for thyroxin, follitropin, creatine kinase isoenzyme MB, and antibody to human immunodeficiency virus (HIV). All of the assays are performed in less than 90 min, many in 30 to 45 min. The technology is highly flexible and is suitable for a variety of formats, from manual to fully automated.

A highly sensitive affinity-column-mediated immunometric assay, as exemplified by digoxin

We describe a highly sensitive heterogeneous enzyme-linked immunoassay in which digoxin is used as the model analyte. An excess of enzyme-labeled monovalent antibody is incubated with sample containing the analyte such that all analyte is rapidly and quantitatively bound. Excess antibody that does not acquire a antigen in its binding site is rapidly removed from the mixture by passage through a porous affinity column containing immobilized analyte (or analog), present in vast excess. Only the labeled monovalent antibody that possesses an antigen in its binding site elutes from the column in the unbound fraction. The label present in this fraction is then quantified. Such an assay is extremely sensitive and obviates the limitations imposed by antibody affinity constants on homogeneous and competitive heterogeneous immunoassays. This assay can be performed rapidly and is readily amenable to automation.

A highly sensitive affinity-column-mediated immunometric assay, as exemplified by digoxin

We describe a highly sensitive heterogeneous enzyme-linked immunoassay in which digoxin is used as the model analyte. An excess of enzyme-labeled monovalent antibody is incubated with sample containing the analyte such that all analyte is rapidly and quantitatively bound. Excess antibody that does not acquire a antigen in its binding site is rapidly removed from the mixture by passage through a porous affinity column containing immobilized analyte (or analog), present in vast excess. Only the labeled monovalent antibody that possesses an antigen in its binding site elutes from the column in the unbound fraction. The label present in this fraction is then quantified. Such an assay is extremely sensitive and obviates the limitations imposed by antibody affinity constants on homogeneous and competitive heterogeneous immunoassays. This assay can be performed rapidly and is readily amenable to automation.