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At least 19 recordsLinked to original sources

PubMed1987

Biosensor for lactate determination in biological fluids. I. Construction and properties of the biosensor.

The preparation of a biosensor for lactate determination is described. The biosensor is based on an immobilized suspension of the aerobic yeast Hansenula anomala, containing flavocytochrome b2 in high activity. The conditions for yeast cultivation were optimized to gain a sufficiently high activity of this enzyme converting lactate in the cells. The properties of the biosensor are compared with those of a sensor based on immobilized enzyme flavocytochrome b2. The yeast lactate biosensor has a sufficient sensitivity and linearity and short time of response. The precision and accuracy of lactate determination as well as the results of comparisons using an enzyme electrode and the spectrophotometric UV-test, enables this biosensor to be used in routine work. Analysis can be performed in blood plasma or whole blood. The stability of the biosensor makes it possible to work for 4 weeks with one yeast cell pellet.

Drug Stability↗

PubMed1991

Acetylcholinesterase fiber-optic biosensor for detection of anticholinesterases.

An optical sensor for anticholinesterases (AntiChEs) was constructed by immobilizing fluorescein isothiocyanate (FITC)-tagged eel electric organ acetylcholinesterase (AChE) on quartz fibers and monitoring enzyme activity. The pH-dependent fluorescent signal generated by FITC-AChE, present in the evanescent zone on the fiber surface, was quenched by the protons produced during acetylcholine (ACh) hydrolysis. Analysis of the fluorescence response showed Michaelis-Menten kinetics with a Kapp value of 420 microM for ACh hydrolysis. The reversible inhibitor edrophonium (0.1 mM) inhibited AChE and consequently reduced fluorescence quenching. The biosensor response immediately recovered upon its removal. The carbamate neostigmine (0.1 mM) also inhibited the biosensor response but recovery was much slower. In the presence of ACh, the organophosphate (OP) diisopropylfluorophosphate (DFP) at 0.1 mM did not interfere with the ACh-dependent fluorescent signal quenching, but preexposure of the biosensor to DFP in absence of ACh inhibited totally and irreversibly the biosensor response. However, the DFP-treated AChE biosensor recovered fully after a 10-min perfusion with pralidoxime (2-PAM). Echothiophate, a quaternary ammonium OP, inhibited the ACh-induced fluorescence quenching in the presence of ACh and the phosphorylated biosensor was reactivated with 2-PAM. These effects reflected the mechanism of action of the inhibitors with AChE and the inhibition constants obtained were comparable to those from colorimetric methods. The biosensor detected concentrations of the carbamate insecticides bendiocarb and methomyl and the OPs echothiophate and paraoxon in the nanomolar to micromolar range. Malathion, parathion, and dicrotophos were not detected even at millimolar concentrations; however, longer exposure or prior modification of these compounds (i.e., to malaoxon, paraoxon) may increase the biosensor detection limits. This AChE biosensor is fast, sensitive, reusable, and relatively easy to operate. Since the instrument is portable and can be self-contained, it shows potential adaptability to field use.

Acetylcholinesterase↗

PubMed1992

Glucose biosensor based on carbon black strips.

Amperometric biosensors for the determination of beta-D-glucose have been constructed. They were based on a porous matrix of carbon blacks--'Ketjenblack' (KB) and 'Shawinigan black' (SB) wet-proofed with polytetrafluorethylene. Glucose-sensitive elements were prepared by subsequent adsorptional immobilization of 1,1'-dimethylferrocene (DMFc) and nickel-ocene (Nc) on 'Shawinigan black' or tetracyanoquinodimethane (TCNQ) on 'Ketjenblack' together with Penicillium chrysogenum glucose oxidase. Maximum surface concentrations of DMFc, Nc and TCNQ on carbon black electrodes were 95, 116 and 151 nmol cm-2. The biosensor based on KB and TCNQ (KB-TCNQ biosensor) could be used at a potential of 0.5 V (vs. Ag/AgCl reference electrode) in the concentration range up to 7 mM. This biosensor possessed an approximately ten times higher sensitivity than the ones based on SB and DMFc (SB-DMFc biosensor) and on SB and Nc (SB-Nc biosensor) which acted at 0.3 V and 0.05 V, respectively. The biosensors were suitable for practical use longer than one week.

Biosensing Techniques↗

PubMed1987

Biosensor for lactate determination in biological fluids. 2. Interference studies.

The selectivity of a yeast lactate biosensor with immobilized cells of aerobic yeast Hansenula anomala was studied. Reducing substances potentially present in blood plasma influenced both enzyme and yeast biosensors in the same way; the highest positive error was observed in the case of uric acid. With respect to the metabolic activity of the yeast cells the biosensor was absolutely specific for lactate during the first two weeks; later on the biosensor responded slightly to some other metabolites, especially some sugars and amino acids. Glucose could cause the highest degree of interference, its effect was however completely eliminated by adding sodium fluoride to the reaction solution. The concentration of other metabolites present in blood plasma is not great enough to call a significant positive error. The results thus support the general use of the yeast lactate biosensor for lactate determination in biological material.

Humans↗

PubMed1990

Optimization of a polypyrrole glucose oxidase biosensor.

An amperometric glucose biosensor was fabricated by the electrochemical polymerization of pyrrole onto a platinum electrode in the presence of the enzyme glucose oxidase in a KCl solution at a potential of +0.65 V versus SCE. The enzyme was entrapped into the polypyrrole film during the electropolymerization process. Glucose responses were measured by potentiostating the enzyme electrode at a potential of +0.7 V versus SCE in order to oxidize the hydrogen generated by the oxidation of glucose by the enzyme in the presence of oxygen. Experiments were performed to determine the optimal conditions of the polypyrrole glucose oxidase film preparation (pyrrole and glucose oxidase concentrations in the plating solution) and the response to glucose from such electrodes was evaluated as a function of film thickness, pH and temperature. It was found that a concentration of 0.3 M pyrrole in the presence of 65 U/ml of glucose oxidase in 0.01 M KCl were the optimal parameters for the fabrication of the biosensor. The optimal response was obtained for a film thickness of 0.17 microns (75 mC/cm2) at pH 6 and at a temperature of 313 K. The temperature dependence of the amperometric response indicated an activation energy of 41 kJ/mole. The linearity of the enzyme electrode response ranged from 1.0 mM to 7.5 mM glucose and kinetic parameters determined for the optimized biosensors were 33.4 mM for the Km and 7.2 microA for the Imax. It was demonstrated that the internal diffusion of hydrogen peroxide through the polypyrrole layer to the platinum surface was the main limiting factor controlling the magnitude of the response of the biosensor to glucose. The response was directly related to the enzyme loading in the polypyrrole film. The shelf life and the operational stability of the optimized biosensor exceed 500 days and 175 assays, respectively. The substrate specificity of the entrapped glucose oxidase was not altered by the immobilization procedure.

Biosensing Techniques↗

PubMed1985

Non-electrode biosensors in clinical biochemistry.

This review covers biosensors based on piezoelectric crystals, optical systems, field effect transistors and thermistors. Piezoelectric crystal or microgravimetric biosensors have been used for immunoassay. Optical biosensors are described in which waveguides are used to transmit changes in optical characteristics or, in an innovative mode, the evanescent wave component of a completely internally-reflected light beam is used to study optical changes. Optical biosensors have been used in immuno and in enzyme-based assays. Field effect transistors detect changes in ion concentrations and have been applied to the detection of biochemical reactions which involve a change in concentration of a specific ion. Thermistors are used to monitor the heat produced as the result of an exothermic enzymatic reaction and this has been applied to the assay of compounds or enzymes of interest. Biosensors may find a role in clinical biochemistry in low volume testing, patient self-testing and in vivo monitoring.

Adsorption↗

PubMed1992

Biosensors: a new realism.

For many years biosensors have been hailed as the solution to many analytical problems. There is general agreement that biosensors offer the potential for easy-to-use, low-cost, rapid analysis. With such versatile, economic, reliable and cheap analytical devices at their disposal, manufacturers in industries as diverse as pharmaceuticals, food and drink, medical diagnostics and defence must surely be reaping vast profits from their biosensor-based products? In fact, biosensors have made only a very modest impact and this article attempts to present a realistic review of their current commercial potential. Consideration is given to the features and benefits of biosensors, the potential application markets, the impact of legislation, the needs of the user and the real commercial potential in the light of these factors and the existing competition.

Biosensing Techniques↗

PubMed1989

Biosensors. A new analytic technology for real-time, on-line biochemical monitoring.

A new technology is evolving that has the potential of improving patient management while substantially reducing the overall cost of health care. This new technology is based on biosensors, analytic microelectronic devices that use biologic detector molecules (e.g., antibodies, enzymes, receptor proteins, lectins, nucleic acids) as the sensing or signal transducing elements. An array of different biosensor configurations are under development, spurred on by recent advances in biotechnology and solid-state electronics. Although not all biosensors can detect their target analytes instantaneously, nor perform continuous measurements, certain biosensors embody both capabilities. Real-time, on-line biochemical monitoring will offer important information heretofore unavailable to the physician. It is also inevitable that biosensor-based instruments will decentralize patient testing, but telemetric systems can maintain the active and necessary involvement of the clinical pathologist.

Biosensing Techniques↗

PubMed1987

Technological advances in bedside monitoring: biosensors.

The need to monitor certain key biochemical parameters in hospitalized patients is driving the development of biosensors, a new class of medical device for real-time, on-line quantitative analysis. A biosensor is a microelectronic device that utilizes a biological molecule (eg, antibody, enzyme, or receptor) as the sensing or signal-transducing element. Biosensors can be configured into simple, rapid, and cost-effective laboratory devices that will allow the clinical pathologist to become even more responsive to the primary care physician. In those instances where measurements on discrete samples do not provide the required information, continuous monitoring with implantable biosensors could provide real-time data on levels of critical endogenous or exogenous substances. By hybridizing recent advances in transdermal substance collection with the analytical capabilities of biosensors, devices for continuous noninvasive monitoring at the bedside can be envisioned. The clinical pathologist can and should play a key role in the clinical evaluation and implementation of such technological advances.

Antibodies↗

PubMed1992

Determination of glutamic acid decarboxylase activity and inhibition by an H2O2-sensing glutamic acid oxidase biosensor.

The catalytic activity of the enzyme L-glutamic acid decarboxylase (GAD) is determined by an amperometric method based on a recently developed glutamate-selective biosensor. The biosensor is composed of an amperometric H2O2 electrode and a biocatalytic membrane containing the enzyme glutamic acid oxidase (GAO). The biosensor allows the direct and continuous measurement of GA levels by monitoring the H2O2 produced at the electrode interface as a coproduct of the GAO-catalyzed GA oxidation to alpha-ketoglutaric acid. Since GA is transformed to gamma-aminobutyric acid and CO2 under the catalytic activity of GAD, the rate of GA consumption in solution, monitored by the GAO biosensor, represents a reliable measure of GAD catalytic activity. Additional experiments performed in the presence of different concentrations of the GAD inhibitor valproic acid have shown the suitability of the proposed approach for the study of GAD inhibitors also. Discussion of the main experimental characteristics of this new analytical method is given in terms of sensitivity, reproducibility, and reliability of the experimental results and ease, time, and cost of operation.

Amino Acid Oxidoreductases↗

PubMed1991

Biosensors for process control.

Biosensors have been extensively studied during the last 20 years, and a myriad of laboratory biosensors have been developed. Improvements are required in biosensor design and performance before they become widely accepted in industrial process monitoring. However, as the biotechnology industry expands, biosensors may become more acceptable because, despite their limitations, they are the only devices capable of delivering the information required.

Biosensing Techniques↗

PubMed1989

Whole-cell biosensors for environmental monitoring.

Concern over the pollution risk to drinking water from industry and agriculture is growing, and the need for continuous on-line monitoring recognised. There is increasing use of living organisms as the sensitive agent to detect the presence of pollutants, and whole-cell biosensors are seen to have particular advantages in such environmental monitoring. The development of a mediated amperometric biosensor, incorporating the cyanobacterium Synechococcus as the biocatalyst, for on-line herbicide monitoring is described. The biosensor is able to detect a wide range of herbicides with sites of action on the photosynthetic electron transport chain, at concentrations down to 20 micrograms litre-1 and possesses a working life of up to 7 days. The use of alginate immobilisation of the biocatalyst to overcome the problems associated with obtaining a realistic shelf life for the biosensor is discussed.

Biosensing Techniques↗

PubMed1989

Rapid determination of the glucose content of molasses using a biosensor.

A knowledge of the sugar content of molasses is of commercial importance to a number of industrial fermentations. Hence the feasibility of using a glucose oxidase biosensor to determine the glucose content of molasses samples was investigated. This method was compared with standard high-performance liquid chromatographic (HPLC) and gas-liquid chromatographic (GLC) procedures and with the use of a commercially available glucose analyser. A good correlation was obtained between the standard acetic anhydride GLC and glucose oxidase biosensor results (correlation coefficient = 0.98). Rapid and accurate measurements could be carried out using the biosensor without the need to employ the sample preparation step required in standard GLC methods. It was concluded that the use of the biosensor technique for the determination of glucose in molasses samples has distinct advantages over conventional methods.

Biosensing Techniques↗

PubMedDate not supplied

Biosensors and the clinical laboratory.

Aside from the economic factors that make biosensors attractive, on-board signal conditioning and signal processing improve the limits of detection and simplify use of the devices. The present discussion summarizes the breadth of biosensor design and application, and the requirements of clinical assay detection. Current sensor research is aimed toward extending the lower limits of detection for nonradioactive immunoassays. The clinical laboratory is in a state of change; operating and instrumentation costs will affect the delivery of diagnostics. Technology will assume a major role in reshaping the clinical laboratory. Biosensors promise to deliver the diagnostic tools for the evolution that is now in progress. The clinical laboratory will no doubt continue to perform chemical profiling and the more specialized tests. The successful implementation of solid-state sensor technology promises to simplify immunoassay procedures, as the autoanalyzer did some 20 years ago for the profiling of blood metabolites. It is likely that more tests will be performed in physicians' offices with the advent of highly automated and cost-effective biosensors. By the use of this technology, practitioners of critical care medicine will be able to assume greater responsibility for diagnostic testing.

Clinical Laboratory Techniques↗

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↗

PubMed1992

Determination of urinary glucose by a flow injection analysis amperometric biosensor and ion-exchange chromatography.

A practical biosensor system has been developed for the determination of urinary glucose using a flow-injection analysis (FIA) amperometric detector and ion-exchange chromatography. Glucose oxidase was immobilized onto porous aminopropyl glass beads via glutaraldehyde activation to form an immobilized enzyme column. On the basis of its negative charge at pH 5.5, endogenous urate in urine samples was effectively retained by an upstream anion-exchange resin column. The biosensor system possessed a sensitivity of 160 +/- 2.4 RU microM-1 (RU or relative unit is defined as 2.86 microV at the detection output) for glucose with a minimum detection level of 10 microM. When applied for the determination of urinary glucose, the result obtained compared very well with that of the widely accepted hexokinase assay. The immobilized glucose oxidase could be reused for more than 1000 repeated analyses without losing its original activity. The reuse of the acetate anion-exchange column before replacement would be about 25-30 analyses. Acetaminophen and ascorbic acid were also effectively adsorbed by the acetate anion exchanger. The introduction of this type of anion exchanger thus greatly improved the selectivity of the FIA biosensor system and fostered its applicability for the determination of glucose in urine samples.

Adult↗

PubMed1988

The nature of biosensor technology.

The biosensor exploits the unique specificity of biological recognition events by coupling an enzyme, antibody or other biorecognition species to a transducing device. Interaction of the biocomponent with substrate or antigen is thus converted into a suitable quantitative output. The development of these biosensors is a multidisciplinary effort, exploiting many of the emerging semiconductor and optics technologies and integrating many traditional assay techniques. The impact of these biosensors is likely to be wide-ranging, with applications in medical and industrial environments as well as a variety of other fields.

Biological Assay↗

PubMed1990

In vivo voltammetry with micro-biosensors for analysis of neurotransmitter release and metabolism.

In vivo voltammetry involves the electrochemical detection of central oxidisable substances in situ. In association with this technique micro carbon fibre electrodes (CFE) are able to separate ascorbic acid (Peak 1) from 3,4-dihydroxyphenylacetic acid (DOPAC) plus dopamine (DA) (Peak 2) and 5-hydroxyindoleacetic acid (5-HIAAA) plus serotonin (5-HT) (Peak 3) in vitro. In vivo these biosensors detect the amine metabolites, due to their high extracellular concentration (microM) compared to the amines (nM). In addition homovanillic acid (HVA) (or 3-methoxytyramine (3-MT) in pargyline-pretreated mice) (Peak 4) and somatostatin (Peak 5) were also measured in vivo. However, potassium-stimulated release of DA has been directly monitored in pargyline pretreated mice. In addition, low concentrations (nM) of DA and 5-HT can now be selectively monitored in vitro with new biosensors coated with Nafion which repels negatively charged species including acid metabolites. In vivo, the combination of the Nafion-CFE and normal CFE allowed simultaneous measurements of release and metabolism of 5-HT, respectively. This permitted the observation that changes in 5-HT release are not necessarily reflected by changes in 5-HIAA levels. At present we are developing a Nafion biosensor to monitor basal extracellular DA. Electron microscope studies have shown radical modifications in the surface and structure of carbon fibres following chemical and electrical pretreatments, which may be involved in the development of sensitivity and selectivity displayed by the pretreated CFE towards electroactive compounds. A new approach for selective detection of neuroamines is the analysis of their stimulated fluorescence using LASER. In vitro, the fluorescence of 5-HT is in fact clearly distinguishable from that of 5-HIAA. The feasibility of this methodology in vivo using fiber optic probes will be explored.

Animals↗