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At least 145 records · Page 8Linked to original sources

PubMed1993

Frey's syndrome analysis with biosensor. A preliminary study.

OBJECTIVE: Objective quantification of Frey's syndrome (gustatory sweating), following total parotidectomy. A biosensoring method of enzymatic electrodes enabling the detection of L-lactate on intact skin with the use of a skin extraction device and enzymatic electrodes is presented and analyzed. DESIGN: A criterion standard study. SETTING: This prospective trial was undertaken at our research laboratory (University of Paris [France]). Parotidectomy was performed in our department, which is a tertiary care center for parotid gland pathology. PATIENTS: Twenty-eight patients with gustatory sweating following total parotidectomy and nine control patients not operated on were asked to take part in this prospective study. MAIN OUTCOME AND MEASURES: Gustatory sweating was assessed in all patients using a clinical scale, the Minor starch iodine test, and the L-lactate biosensoring method. RESULTS: Instrumentation and assay procedure for the L-lactate biosensoring method are detailed. Statistical analysis of data was performed using the Kruskal-Wallis H Test and the Mann-Whitney U Test. Results demonstrate that this method enables objective measurement of the L-lactate on skin without the need for chemical reagents, continuous nondestructive analysis in real time, and physiological dynamic monitoring of the L-lactate rate of production after stimulus. Data achieved strongly suggested that the aberrant regeneration theory is the main clue to Frey's syndrome pathogenesis. CONCLUSION: This safe, reliable, noninvasive, objective, and highly sensitive method provides an investigative tool for clinicians as well as physiologists involved with patients presenting gustatory sweating following parotid gland surgery.

Adenoma, Pleomorphic↗

PubMed1999

Mixed-valence compound-based biosensor.

A cobalt(II)hexacyanoferrate-based biosensor has been prepared simply by codeposition of an enzyme, together with the electrochemical formation of a cobalt (II)hexacyanoferrate compound electrochemically. The compound can be generated at a constant potential of -0.05 V (vs. Ag/AgCl). This compound possesses the catalytic property of reducing hydrogen peroxide to water at the operating potential of 0.0 V vs. Ag/AgCl. The mixed-valence compound-based biosensor possesses an unique interference-independent feature, which is important for biomedical application; this feature is attributed to the low overvoltage characteristic of cobalt (II)hexacyanoferrate. The electrochemical glucose biosensor responds to a series of glucose injections with linearity up to 5 mM (with correlation coefficient R = 0.9999) and the sensitivity of the linear portion is 733 nA/(cm2 x mM). The detection limit is 2 x 10(-6)M (S/N = 3). Both the potential-dependent electron transfer rate constant and the apparent Michaelis-Menten constant were studied in rotating disk experiments. The apparent Michaelis-Menten constant, Km' calculated from the slope of the "Lineweaver-Burke" type reciprocal plot is 28 mM. A fast-response characteristic is observed in the rotating disk experiment and the 95% response time is 14.5 sec. No response was observed from the addition of either 2 x 10(-4)M galactose, acetaminophen, ascorbic acid, uric acid, cysteine, tyrosine, dopamine, or 1,4-dihydroxyquinone in the absence and/or in the presence of 5 x 10(-4)M glucose.

Biosensing Techniques↗

PubMedDate not supplied

Principles and applications of flow injection analysis in biosensors.

In practical applications biosensors are often forced to operate under less than optimal conditions. Because of their construction, and the physical processes and chemical reactions involved in their operation, compromise conditions are frequently required to synchronize all events taking place. Therefore, and in order to implement functions such as periodic calibration, conditioning and possible regeneration of the biosensor, and, very importantly, to yield the freedom to select the optimum detection means, it is advantageous to use these devices in a flow-through mode, particularly by employing the flow injection (FI) approach. The capacity of FI, as offering itself as a complementary facility to augment the performance of biosensors, and in many cases as an attractive alternative, is demonstrated by reference to selected examples, comprising assays based on enzymatic procedures with optical and thermal detection procedures, and via description of a recently introduced technique for immunoassays, termed flow injection renewable surface immunoassays, which promises to entail powerful potentials and to yield compatible or better economy of operation than existing approaches.

Biosensing Techniques↗

PubMedDate not supplied

Biosensors in flow-injection systems for biomedical analysis, process and environmental monitoring.

This paper presents the construction of various biosensors using thin-film layers incorporated in flow injection devices, providing automated systems for biomedical analysis, process and environmental monitoring. A urease sensor has been developed in conjunction with a flow injection system for the automatic determination of urea. Use of the spraying immobilization technique gives rise to a response time of a few seconds, which allows sample throughputs up to 200 h-1. With a penicillin biosensor adapted in an appropriate cell detection, on-line measurements of penicillin V in the fermentation broth are achieved during the whole fermentation process; the results are compared with the HPLC method. Linearity, sensitivity and reproducibility of the biosensor are studied with regards to sample dilution in a stirred flow detection cell to provide optimal operating conditions. Measurements without any change in parameters are obtained during the whole fermentation process. Acetylcholinesterase sensors have been used in batch systems for the determination of pesticides, but they require large amounts of substrate. When those enzyme sensors are combined with flow injection systems, only small volumes (100 microliters) of substrate are injected into the carrier stream and an automated system can be obtained for continuous control of water quality.

Biosensing Techniques↗

PubMedDate not supplied

Ligand loading at the surface of an optical biosensor and its effect upon the kinetics of protein-protein interactions.

Optical biosensors are finding increasing use in the determination of kinetic and equilibrium constants for a variety of biomolecular interactions. Usually these biosensors require one biomolecule, the ligand, to be covalently attached to a hydrogel matrix which itself is bonded to the sensing surface. The ligands partner, the ligate, then binds from solution resulting in a measurable change in response which the instrument records as a function of time. Although in many cases, optical biosensors are used in order to obtain parameters that relate to interactions in solution, it is becoming clear that measurements involving the interaction of ligate with immobilized ligands on surfaces require careful experimental design. Here we report on how the density of ligand loading within the hydogel matrix affects the measured interaction kinetics. It is found that crowding of ligand within this matrix results in a significant reduction in the measured association rate constant, with a corresponding effect in the calculated overall affinity. However, measurements at low ligand loadings show association rate constants that are comparable to those measured in solution. Clearly, where this comparison is required, it is important to perform measurements under such conditions.

Biosensing Techniques↗

PubMed1998

High-density immobilization of an antibody fragment to a carboxymethylated dextran-linked biosensor surface.

There are numerous chemical methods published that enable protein coupling to carboxymethyl (CM) dextran. Here we have taken traditional amine coupling using N-hydroxysuccinimide (NHS) and N'-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and coupled an antibody fragment (scFv) to CM dextran at a very high density. Using an upgraded BIAlite from Biacore AB, more than 7000 RU of scFv was coupled to a CM dextran biosensor chip. In addition, scanning electron microscopy was performed on CM dextran biosensor chips following amine coupling of 30 nm gold anti-IgG particles. This showed that amine coupling was uniform across the biosensor chip surface. Calculations show that 7620 RU of an scFv coupled to such a surface results in a mean distance between binding sites of 8.8 nm. This equates to a packing volume of approximately 20% of the available space occupied by the antibody fragment. Comparisons made with densities of covalently coupled IgG show that a greater number of antibody fragment molecules can be coupled per unit area. This is most likely due to the smaller size of an antibody fragment (scFv), which has a volume of less than 20% of an IgG molecule. The significance of these findings is discussed.

Animals↗

PubMedDate not supplied

Biosensor analysis of the interleukin-2 receptor complex.

Surface plasmon resonance (SPR) biosensor technology has been a significant addition to the evolution and refinement of methods to study macromolecular interactions. Prior to the advent of SPR, we employed a variety of biochemical and biological techniques to study the interleukin-2/interleukin-2 receptor system (IL-2/IL-2R). By combining site-directed mutagenesis, equilibrium and kinetic radioligand binding, and competitive biological assays, we and others had begun to understand many aspects of the structure-activity relationships of the IL-2/IL-2R system. Due to the complexity of the IL-2R, cell-based assays proved limited in their ability to provide quantitative information on the binding characteristics of subclasses of the IL-2 receptor. SPR technology promised to be a new and powerful approach to the quantitative analysis of complex receptor systems. To demonstrate the feasibility of this technology, we employed Biacore analysis to investigate the ligand binding characteristics of novel, pre-assembled, IL-2R coiled-coil complexes. The results of these studies, although limited by instrumentation and data analysis, clearly established the utility of this method. Subsequently, by incorporating advancements in both of these areas, we have been able to carry out detailed kinetic analyses of the binding properties of individual IL-2R subunits as well as heteromeric complexes on the surface of a biosensor. Therefore, SPR biosensor analysis combined with other established analytical methods has proven to be a powerful tool for the analysis of complex hematopoietic receptor systems. Published in 1999 by John Wiley & Sons, Ltd.

Animals↗

PubMed1995

A biosensor concept based on imaging ellipsometry for visualization of biomolecular interactions.

A new type of optical biosensor system is proposed and its application to detection of antigen-antibody complexes on a silicon substrate is demonstrated. The biosensor system is utilizing specificities of biomolecular interactions in combination with protein patterned surfaces. Visualization of the thickness distributions of thin layers (protein patterns) on a surface is achieved by using imaging ellipsometry. This technique uses a CCD camera whereby an ellipsometric analysis of a large surface can be made. The biosensor system has the advantages of high spatial resolution, fast data acquisition, and simplicity in use.

Adsorption↗

PubMed1996

Quantitating staphylococcal enterotoxin B in diverse media using a portable fiber-optic biosensor.

A new, portable fiber-optic biosensor has been used to detect staphylococcal enterotoxin B, a causative agent of food poisoning, at levels as low as 0.5 ng/ml in buffer. The toxin (SEB) can also be detected and quantitated in other relevant media: human serum, urine, and aqueous extract of ham. The level of toxin, from 5 to 200 ng/ml, can be accurately predicted in these media by calibrating each fiber and by comparing results to a single standard curve based on toxin in buffer. The quantitative fluorescent sandwich immunoassay provides results in 45 min; qualitative results are provided in 15-20 min. Using a blender and a benchtop centrifuge, fast, simple aqueous extracts of contaminated ham samples were prepared and tested. Ham spiked with 5 or 40 micrograms SEB per 100 g food resulted in biosensor readings indicative of 11 or 69% recovery of the toxin, respectively. Finally, the SEB assay is highly specific; SEA and SED give only 2-3% of the signal at 5000 ng/ml as SEB gives at 1000 ng/ml. This specific, sensitive assay for SEB on the portable fiber-optic biosensor permits easy monitoring of clinical samples or on-site analysis of suspect food samples.

Animals↗

PubMed2001

An organically modified silicate-based ethanol biosensor.

A novel electrocatalytic ethanol biosensor using ferrocene-encapsulated palladium (Pd)-linked organically modified sol-gel glass (ormosil) is reported. The alkoxy precursors used to prepare the new ormosil-based electrocatalytic biosensor are Pd-linked glycidoxypropyltrimethoxysilane and trimethoxysilane. Pd-glycidoxypropyltrimethoxysilane (black solution) is made by mixing aqueous solutions of palladium chloride and glycidoxypropyltrimethoxysilane. The new ormosil is made using a Pd-linked silane precursor, trimethoxysilane, an aqueous solution of ferrocene monocarboxylic acid, and HCl. Alcohol dehydrogenase (ADH) is assembled over the ferrocene-ormosil layer using polyvinyl alcohol and then protecting the immobilized enzyme layer using Millipore filter membranes (pore size 1 microm). The electrocatalytic response of immobilized ADH, soluble nicotinamide adenine dinucleotide, and Pd-linked ormosil-encapsulated ferrocene is then observed. The electrocatalytic oxidation of NADH and the subsequent ADH-catalyzed formation of NADH are monitored electrochemically. Typical results recorded after the addition of varying concentrations of ethanol are reported; however, the sensor is sensitive to other alcohol and known ADH-sensitive substrates. The stability and reproducibility of the new ethanol biosensor are reported.

Alcohol Dehydrogenase↗

PubMed2001

An amperometric cellobiose dehydrogenase-based biosensor can be used for measurement of cellulase activity.

The hemoflavoenzyme cellobiose dehydrogenase (CDH, EC 1.1.99.18) from Phanerochaete chrysosporium has been used in an amperometric redox polymer-based biosensor. Used in conjugation with a FIA system this biosensor can replace colorimetric assays for measuring cellobiose liberated from cellulose in a series of cellulase-containing samples. The biosensor gave the same result as the Somogyi-Nelson method in a less time-consuming and laborious manner. The two methods showed about the same precision.

Biosensing Techniques↗

PubMed1997

Binding Kinetics for Biosensor Applications Utilizing Fractals: A Categorization

Analyte-receptor binding reactions occurring on biosensor surfaces are categorized using a fractal analysis. Both a single- and a dual-fractal analysis are utilized to describe the analyte-receptor binding kinetics. The three categories presented to describe the binding kinetics include (a) case I-only a single-fractal analysis is utilized, (b) case II-a single- and a dual-fractal analysis are utilized (implying a change in the binding mechanism), and (c) case III-only a dual-fractal analysis is utilized. This is an initial attempt to categorize surface binding kinetics. The categorization provides one possible means of classifying analyte-receptor reactions occurring on biosensor surfaces. The analysis should help to improve biosensor performance parameters. The analysis is, in general, extendable to analyte-receptor reactions occurring on other surfaces.

Journal Article↗

PubMed1999

A Single and a Dual-Fractal Analysis of Analyte-Receptor Binding Kinetics for Surface Plasmon Resonance Biosensor Applications.

The diffusion-limited binding kinetics of analyte in solution to either a receptor immobilized on a surface or to a receptorless surface is analyzed within a fractal framework for a surface plasmon resonance biosensor. The data is adequately described by a single- or a dual-fractal analysis. Initially, the data was modeled by a single-fractal analysis. If an inadequate fit was obtained then a dual-fractal analysis was utilized. The regression analysis provided by Sigmaplot (32) was used to determine if a single fractal analysis is sufficient or if a dual-fractal analysis is required. In general, it is of interest to note that the binding rate coefficient and the fractal dimension exhibit changes in the same direction (except for a single example) for the analyte-receptor systems analyzed. Binding rate coefficient expressions as a function of the fractal dimension developed for the analyte-receptor binding systems indicate, in general, the high sensitivity of the binding rate coefficient on the fractal dimension when both a single- and a dual-fractal analysis is used. For example, for a single-fractal analysis and for the binding of human endothelin-1 (ET-1) antibody in solution to ET-115-21.BSA immobilized on a surface plasmon resonance (SPR) surface (33), the order of dependence of the binding rate coefficient, k, on the fractal dimension, Df, is 6.4405. Similarly, for a dual-fractal analysis and for the binding of 10(-6) to 10(-4) M bSA in solution to a receptorless surface (direct binding to SPR surface) (41) the order of dependence of k1 and k2 on Df1 and Df2 were -2.356 and 6.241, respectively. Binding rate coefficient expressions are also developed as a function of the analyte concentration in solution. The binding rate coefficient expressions developed as a function of the fractal dimension(s) are of particular value since they provide a means to better control SPR biosensor performance by linking it to the degree of heterogeneity that exists on the SPR biosensor surface. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Exploring biomolecular recognition using optical biosensors.

Understanding the basic forces that determine molecular recognition helps to elucidate mechanisms of biological processes and facilitates discovery of innovative biotechnological methods and materials for therapeutics, diagnostics, and separation science. The ability to measure interaction properties of biological macromolecules quantitatively across a wide range of affinity, size, and purity is a growing need of studies aimed at characterizing biomolecular interactions and the structural elements that drive them. Optical biosensors have provided an increasingly impactful technology for such biomolecular interaction analyses. These biosensors record the binding and dissociation of macromolecules in real time by transducing the accumulation of mass of an analyte molecule at the sensor surface coated with ligand molecule into an optical signal. Interactions of analytes and ligands can be analyzed at a microscale and without the need to label either interactant. Sensors enable the detection of bimolecular interaction as well as multimolecular assembly. Most notably, the method is quantitative and kinetic, enabling determination of both steady-state and dynamic parameters of interaction. This article describes the basic methodology of optical biosensors and presents several examples of its use to investigate such biomolecular systems as cytokine growth factor-receptor recognition, coagulation factor assembly, and virus-cell docking.

Artifacts↗

PubMed1997

Biosensors for food analysis.

Concerning speed, cost and on-line capabilities, biosensors offer attractive alternatives to existing methods for food analysis. They make monitoring and control of manufacturing processes possible. Furthermore, portable biosensors could be used for monitoring in manufacturing, retail and distribution of foods. An overview is given about existing biosensors for foodstuffs that could find applications in food industry.

Acids↗

PubMed1991

A yeast biosensor for glucose determination.

A yeast potentiometric biosensor for glucose determination is described. After induction of glycolytic enzyme synthesis a cell suspension of the yeast Hansenula anomala is retained in calcium alginate gel on the surface of a glass electrode. This biosensor gives a Nernstian response in glucose concentration of 5 x 10(-4)-5 x 10(-3) mol/l with a response time of 5 min and a life-time of at least 2 months. Mannose and fructose are the only significantly interfering substances. The biosensor was used for measurement of glucose concentration in urine with results comparable to those obtained by a photometric enzymatic method.

Biological Assay↗

PubMed1993

A microbial biosensor system for dihalomethanes.

A biosensor system able to measure dichloromethane (DCM) and other dihalomethanes has been developed. The analysis is based on Hyphomicrobium DM2 cells immobilized in alginate. A combination of transducers consisting of a flow-calorimeter followed by a chloride-sensitive electrode has been used. By this design it was possible to monitor different aspects of the cell metabolism from one and the same pulse of substrate. The detection limit for the biosensor was 0.1 microM dichloromethane. The biosensor system can be used for continuous measurements in a sample stream.

Bacteria↗

PubMed1993

Polymer materials in biosensors.

Fundamentals and application examples of polymeric materials in different types of biosensors and presented and discussed in view of their molecular structure and biosensor design and construction. The role of a series of polymers with respect to their typical application and their specific properties, like sensitivity and stability, is highlighted. Future trends of polymer materials for biosensors in the area of medical and environmental applications are outlined.

Biosensing Techniques↗