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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↗

PubMed1990

Flow injection analysis and biosensors: applications for biotechnology and environmental control.

Our experience in industrial bioprocess monitoring and environmental control let us develop a concept for biosensor research which distinguishes itself from other, more popular, approaches. Biosensors must improve and/or simplify existing state-of-the-art analysis systems. Only the parallel development of biosensors and their complementary metrology leads to industrially sound solutions. The combination of flow injection analysis with immobilized enzymes in the form of enzyme columns is already used today for the solution of on-line analytical problems in bioprocesses and environmental control.

Biosensing Techniques↗

PubMed1996

Analysis of kinetic data of antibody-antigen interaction from an optical biosensor by exponential curve fitting.

An optical biosensor system employing a resonant mirror (RM), with a stirred cuvette has been used to follow the interaction of a recombinant antibody fragment with its antigen, hen egg lysozyme. The data generated by the biosensor were analysed in order to determine the kinetic constants for the interaction using a linear transform (derivative analysis). For comparison the data were also analysed using an exponential curve fitting routine. It was demonstrated that the exponential curve fitting method produced results which were in agreement with the existing linear transform method. It was also shown that early fitting of the association phase response, using the exponential curve fitting routine between 0 and 70 s after sample addition, yielded sufficient information to provide a prediction of Kon. The potential use of the optical biosensor for the rapid monitoring of protein production and purification is discussed.

Animals↗

PubMed1996

An analysis of antigen-antibody binding kinetics for biosensor applications utilized as a model system: influence of non-specific binding.

The influence of non-specific binding on the specific binding of antigen in solution to antibody immobilized on a biosensor surface is presented for first-, one and a half-, second-, and other order reactions occurring under external diffusion-limited conditions. Both single-step and dual-step binding of antigen to antibody is considered. For a half-order reaction the value of the ratio of non-specific binding to specific binding (alpha) does not affect the rate of specific binding since a single curve represents the binding curve for alpha = 0 to 0.5. An increase in the alpha value leads to a decrease in the rate of binding and in the amount of antigen bound specifically to the antibody on the surface for first-, one and a half-, and second-order reactions. Also, an increase in the reaction order increases the sensitivity of the specific binding to the alpha value. An increase in the antigen concentration in solution increases the amount and the rate of specific binding for first-, one and a half-, and second-order reactions. The introduction of non-specific binding leads to complexities in the specific binding of the antigen for the one and half- and second-order reactions as the antibody concentration on the surface is varied. When non-specific binding is present there is an optimum value of the antibody concentration on the surface that yields the maximum rate and amount of antigen specifically bound for one and a half- and second-order reactions. Though this optimum amount of antibody immobilized on the surface is the same for the one and a half- and second-order reactions, it is different for different alpha values. No such complexities are observed for first-order reactions. The inclusion of non-specific binding in the analysis provides a more realistic picture of the binding of the antigen in solution to the antibody immobilized on the surface. The figures that show the numerically calculated binding rates for different orders when non-specific binding is present, represent the most useful part of the analysis for readers who are interested in constructing biosensors, and should assist in the control and manipulation of these interactions at the surface. These curves can be used to interpret a far from ideal binding of antigen to an immobilized antibody surface or vice versa. More-or-less all of the analysis should also be applicable to analytical systems that would not be classified as biosensors (that is, immuno and receptor assays).

Antibodies↗

PubMed1996

Toxicity order of cholanic acids using an immobilised cell biosensor.

There is considerable published evidence of the use of cells of various species to evaluate the toxicity of numerous compounds, many of pharmaceutical interest. The coupling of cell colonies with a suitable transduction device has led to the development in recent years of toxicity biosensors based on the alteration of a process or a cell metabolic function by the toxic substance under examination. A biosensor based on immobilised yeast cells (Saccharomyces cerevisiae) has been developed recently in this department for the purpose of performing a rapid toxicity test in aqueous environmental matrices. This biosensor has now been used in the toxicity screening of a number of sodium salts of conjugated and free cholanic acids. The "toxicity degree" scale, which was found by placing in decreasing order the values of the slopes of the straight lines obtained by quantifying changes in the behaviour of the respirometric curve, plotted before and after incubation, using known concentrations of cholanic acid sodium salts, was: deoxycholic acid > chenodeoxycholic acid > ursodeoxycholic acid > cholic acid, for free cholanic acids; and glycodeoxycholic acid > glycochenodeoxycholic acid > glycocholic acid, for glycocholanic acids. These values are in good agreement with published toxicity data obtained in vitro. This sensor can thus be considered to provide a valid instrument for the preliminary evaluation of the toxicity of organic compounds or drugs.

Biosensing Techniques↗

PubMed1991

A microbial biosensor for trimethylamine using Pseudomonas aminovorans cells.

A biosensor system based on the difference in the oxygen uptake response of two microbial electrodes was developed to monitor trimethylamine (TMA). The first electrode, constructed using Pseudomonas aminovorans grown on TMA, was sensitive to TMA, trimethylamine N-oxide (TMAO), dimethylamine (DMA) and monomethylamine (MMA). The second electrode responding to TMAO, DMA and MMA was prepared using Ps. aminovorans grown on TMAO. The difference in oxygen uptake was linearly related to the TMA concentration in the range of 5-26 microM. The minimum detectable level was 2.6 microM and the relative standard deviation was determined to be 14% for 16 repeated analyses. When operated and stored at 30 degrees C, the response of the system was stable for only 2 days. However, when the biosensor system was operated at 30 degrees C but stored overnight at 4 degrees C, the system was stable up to 20 days. The biosensor system was applicable for the determination of TMA in fish tissue extracts and the results compared well with those determined by HPLC.

Animals↗

PubMed1992

Monitoring glutamine in mammalian cell cultures using an amperometric biosensor.

An amperometric biosensor has been developed for monitoring glutamine in the pulsed-batch cultivation of murine hybridoma cells. Glutamine oxidase was cross-linked with bovine serum albumin (BSA) via glutaraldehyde activation and deposited on a preactivated nylon membrane. Glutaminase was then immobilized on the protein layer and the resulting membrane was attached to the sensing area of a hydrogen peroxide probe (platinum vs silver/silver chloride polarized at +0.7 V). An orthogonal test was performed to optimize the activity of the membrane for glutamine with respect to the concentrations of glutamate oxidase, BSA, glutaminase and glutaraldehyde. There was an excellent linear relationship between the biosensor's response and glutamine in the range 0.1-3 mM. The determination of glutamine could be performed in 2 min and each membrane was reused for at least 300 consecutive analyses. The data obtained also agreed well with those high-performance liquid chromatography, thus validating the applicability of the biosensor.

Amino Acid Oxidoreductases↗

PubMed1993

Improvement of the selectivity of an FIA amperometric biosensor system for glucose.

A flow injection analysis (FIA) biosensor system has been developed for the determination of glucose from urine, blood plasma and foodstuffs. Glucose oxidase was immobilized onto porous aminopropyl glass beads via glutaraldehyde activation to form an enzyme column. The hydrogen peroxide released from the conversion of glucose to gluconic acid was monitored by a platinum electrode vs. silver/silver chloride poised at +700 mV. As a novel aspect to the improvement of the selectivity of the biosensor system, an anion exchange column was placed upstream to remove uric acid, ascorbic acid or acetaminophen, three major electroactive interfering substances which usually occur in urine and blood plasma. Among several resins tested, the effective adsorption of uric and ascorbic acids could be accomplished using an acetate anion exchanger, and the selectivity coefficient was pH dependent. The binding of acetaminophen to the resin was much less efficient and, in all cases, the selectivity coefficient was independent of the operating temperature up to 37 degrees C. When applied to real samples, the data obtained by the biosensor system compared well with those of the standard hexokinase assay. The immobilized glucose oxidase could be reused for at least 2000 repeated analyses without loss of its original activity.

Acetaminophen↗

PubMed1993

Dynamic concentration challenges for biosensor characterization.

A method and apparatus are described for characterization of the steady state and dynamic response of biosensors. The apparatus produces a steady stream of homogeneously mixed analyte whose concentration can be fixed at discrete values or varied continuously. The device is ideally suited for continuously operated biosensors, but is also effective for biosensors that operate in discrete sampling modes. The system permits simultaneous testing of several sensors and determination of the accuracy, precision and repeatability of sensor response. The characteristics of this testing apparatus were validated with ferrocyanide and glucose as indicators. As an example of use of the apparatus, concentration ramps were created and used to complement conventional step changes for characterizing an implantable glucose sensor. The ramp rate can be adjusted easily by scaling the apparatus to simulate the rate of concentration change anticipated during actual monitoring situations.

Animals↗

PubMed1994

Thin-film conductometric biosensors for glucose and urea determination.

The characteristics of the developed conductometric biosensors for urea and glucose determination are described. Conductometric transducers based on thin-film interdigitated metal (Au, Cr, Cu, Ni) electrodes were studied, and enzymes urease and glucose oxidase were used for the selective membranes formation on the chips having gold electrodes. The influence of ionic strength and buffer capacity of the samples on the biosensors response in kinetic and steady-state modes of measurements was thoroughly tested. It was shown that the kinetic response of the sensors does not depend on the buffer capacity of the analyzed sample. In basic features the performance of the developed biosensors is rather close to that of respective enzyme field effect transistor, though the former are much superior when the technological complexity of the transducer itself is considered and taking into account that conductometric sensors require no reference electrode.

Biosensing Techniques↗

PubMed1995

Enzyme biosensor for urea based on a novel pH bulk optode membrane.

A new, absorbance-based enzymatic biosensor membrane for determination of urea is described. A lipophilic, fully LED- and diode laser-compatible pH sensitive dye was incorporated into a plasticized, carboxylated poly(vinyl chloride) membrane and served as the optical transducer of the sensor. Urease was covalently linked to the surface of the pH bulk optode membrane to form a very thin cover. The resulting biosensor membrane allows rapid determination of urea over the 0.3 to 100 mM range. The reproducibility, stability, and effects of pH and buffer concentration on the response of sensor are reported. The preparation of the pH transducer and the immobilization of the enzyme are simple and may easily be adopted to other biosensor types.

Animals↗

PubMed1996

Enzyme support systems for biosensor applications based on gold-coated nylon meshes.

A novel experimental protocol for enzyme immobilization based on the use of a very permeable support is described and applied to the development of an acetylcholinesterase (AChE) based biosensor. In this system, the enzyme was immobilized onto a gold-coated nylon mesh via a self-assembled monolayer of a bifunctional reagent, cystamine, preadsorbed onto the gold surface. This support has been characterized by optical microscopy and electrochemical measurements of permeability. In the assembled biosensor, the AChE modified mesh was placed over a glassy carbon electrode and the response to 4-aminophenylacetate, used as substrate, was monitored via the enzymatic reaction product, 4-aminophenol, by oxidation at +0.25 V vs. SSCE. This approach to biosensor design has been extended to the determination of organophosphorus and carbamate pesticides by their inhibition of AChE enzymatic activity.

Acetylcholinesterase↗

PubMed1996

Lactate solid-state biosensor with multilayer of electrodeposited polymers for flow-injection clinical analysis.

In the lactate biosensor, electrodeposited poly(o-phenylenediamine) serves as a convenient matrix for the immobilization of lactate oxidase, but does not provide sufficient discrimination from several interfering species present in physiological fluids. Their effect, however, can be eliminated by additional modification of the working Pt electrode with a bilayer of electrodeposited polypyrrole/polyphenol. Despite continued decrease in biosensor sensitivity, the newly developed three-layer solid-state biosensor was successfully applied in flow-injection determination of lactate in both undiluted and diluted human blood serum samples over a 10 day period. For the lactate concentration range 0.2-5.0 mM in several series of measurements the correlation coefficient values for comparison with photometric determination using a DuPont dimension clinical analyzer were between 0.96 and 0.99. The reproducibility measured for 1:10 diluted serum was 0.6%. The detection limit was estimated as 2 microM.

Acetaminophen↗

PubMed1996

A fractal analysis of the influence of non-specific binding on antigen-antibody binding kinetics for biosensor applications.

A fractal analysis of the influence of non-specific binding on the specific binding of antigen in solution to antibody immobilized on a biosensor surface is presented for first-, one and a half-, second, and other-order reactions occurring under external diffusion-limited conditions. Both single-step and dual-step binding of antigen in solution to antibody immobilized on the surface is considered. For a first-order reaction, an increase in the fractal parameters, b, leads to a decrease in the amount of antigen in solution bound specifically to the antibody on the surface when non-specific binding is either absent or present. The presence of non-specific binding leads to a decrease in the amount of antigen bound to the antibody on the surface. For a one and a half- and for second-order reactions and when non-specific binding is either absent or present to a small degree (alpha = 0.01), an increase in the fractal parameter, b, leads to a decrease in the amount of antigen bound specifically to the antibody immobilized on the biosensor surface. However, for an alpha value of 0.1, the maximum rate and the amount of antigen bound specifically to the antibody immobilized on the biosensor surface is obtained for fractal parameter values of 0.2 and 0.4, and 0.4 for the one and a half- and for second-order reactions, respectively. Apparently, some amount of heterogeneity is helpful in obtaining the optimum amount and rate of antigen in solution bound specifically to the antibody on the surface for reaction orders higher than one. The applicability of the approach to real antibody surfaces is demonstrated.

Antigen-Antibody Reactions↗

PubMed1996

Application of biosensor for monitoring galactose content.

The quality and quantity of different sugars play a very important role in studying the carbohydrate metabolism of yeast. During the bioprocesses there is a need to follow the concentrations of these sugars. Authors have reported on the development of biosensors for determination of glucose and maltose previously. The aim of this research was to construct a sensor for determining galactose in fermentation broths to prepare the basis for an online monitoring system. Using a modified thin-layer enzyme cell connected to an electrochemical detector cell, a biosensor has been developed for this purpose. Galactose was oxidized with immobilized galactose oxidase enzyme (EC 1.1.3.9) and the hydrogen peroxide generated during the enzyme reaction was determined with an amperometric detector. The parameters for the biochemical and electrochemical reactions were optimized. The pH optimum of 6.6 was found when using phosphate buffer. The buffer solution completed by micro elements (Mg2+, Se2+) gave more stable signs. The activities for raffinose, lactose, glycerol and dihydroxyacetone were 68, 16, 6 and 430%, respectively. With the thin-layer cell more than 900 samples were measured in 6 weeks. Samples obtained from different fermentations were measured with the newly developed galactose sensor and the results were compared with the standard UV method. The correlation coefficient was 0.991. The results showed that the application of the new biosensor was successful.

Biosensing Techniques↗

PubMed1996

Electrochemical biosensors for medicine and ecology.

Research results obtained in the last 3 years in the area of electrochemical amperometric biosensors are presented. Selective electrochemical biosensors are proposed on the basis of investigations of electrode materials, electrolyte content, selective properties of polymer materials and mediators influence. Biosensor parameters for determination of glucose, phenol and biological oxygen demand are described.

Biosensing Techniques↗

PubMed1995

Metrological opportunities of the dynamic mode of operating an enzyme amperometric biosensor.

An algorithm for generating calibration curves that reflects the peculiarities of the dynamic mode of operating of the amperometric biosensor, created on the base of numerical simulations of the sensor behaviour, is proposed. The most important steps are: selection of the informative quantity about the sensor current versus time relationship and the calibration curve processing. Five different informative quantities are tested as well as two ways of representation of calibration curves. The object of study is enzyme catalyzed selective reaction. The values of the kinetic constants used reflect the conversion of glucose to gluconolacton catalyzed by glucose oxidase (GOD) and catalase (CAT). The results show that sensors with different metrological characteristics can be created by means of a selection of informative quantity of the signal of one biosensor transducer. In addition there appears to be a possibility of facilitating the calibration procedure and prolonging the life of the biosensor.

Algorithms↗

PubMed1997

Evaluation of a miniaturized thermal biosensor for the determination of glucose in whole blood.

A miniaturized thermal biosensor has been evaluated as part of a flow-injection analysis system for the determination of glucose in whole blood. Glucose was determined by measuring the heat evolved when samples containing glucose passed through a small column with immobilized glucose oxidase and catalase. Samples of whole blood (1 microliter) can be measured directly, without any pretreatment. The correlation in the response between the thermal biosensor, the Reflolux S meter (Boehringer Mannheim), the Granutest 100 glucose test kit (Merck Diagnostica) and the Ektachem (Kodak) instrument was evaluated. The influence of the hematocrit value and of possible interferences is reported. The correlation measurements show that the thermal biosensor calibrated with aqueous glucose standards generally gives lower values on blood glucose than the reference methods calibrated for serum or blood measurements. Mean negative biases range from 0.53 to 1.16 mmol/l. Differences in sample treatment clearly complicate comparisons and the proper choice of reference method. There was no influence from substances such as ascorbic acid (0.11 mmol/l), uric acid (0.48 mmol/l), urea (4.3 mmol/l) and acetaminophen (0.17 mmol/l) on the response to 5 mmol/l glucose. The hematocrit value does not influence the glucose determination, for hematocrit values of between 13 and 53%.

Biosensing Techniques↗