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PubMedDate not supplied

[Study of immobilization and properties of urease for creation of a biosensor based on semiconductor structures].

Many-sided investigations of urease immobilization methods were carried out to create the biosensor devices on the base of semiconductor structures. Special attention was concentrated on the biomembrane formation by means of urease and bovine serum albumin (BSA) cross-linking by gaseous glutaraldehyde. Optimal conditions for the formation process were selected which preserve about 20% of total urease activity after the cross-linking. The properties of enzyme immobilized by the above-mentioned method have been comprehensively studied. They included the urease activity dependence on pH, ionic strength, incubation buffer capacity as well as the enzyme stability during its functioning, storing and thermoinactivation. As was shown, for immobilized ureas Km value for urea at pH 7.0 and 20 degrees C is 1.65 time less than for free enzyme. In the presence of EDTA (1 mM) the enzyme activity in the biomembrane is practically unchanged under a month storing. Biomembrane possesses good adhesion to silicon surface and its swelling level under different conditions does not exceed 35%. The conclusion is made about the prospects of the used method of biomembrane formation for biosensor technology based on semiconductor structures.

Enzyme Stability↗
PubMed1992

Development of a non-invasive transcutaneous blood glucose monitoring method using an ISFET biosensor.

A transcutaneous blood glucose monitoring method has been developed by combining an SOS/ISFET (silicone-on-sapphire/ion sensitive field effect transistor) biosensor with an SEF (suction effusion fluid) collecting technique. The SEF collecting cell has a stainless steel mesh at its bottom which is kept in a weak vacuum condition so as to suck up transcutaneous SEF and deposit it in a reservoir above. An ISFET biosensor, consisting of immobilized enzyme membranes, enables the detection of glucose concentrations in very small samples. The method has been successfully applied to non-invasive monitoring of human blood glucose levels during tests involving 75 g OGTT (oral glucose tolerance test). Glucose concentrations measured with SEF showed good correlation with those obtained directly from serum. Results suggest the feasibility of a portable blood monitoring system.

Biosensing Techniques↗
PubMed1991

Development of biosensors for immunoassays.

Biosensors represent a new generation of analytical instruments incorporating a biological sensing element in contact with a physical transducer and an output device. The biological element may be a whole organism, an organelle, an enzyme, an antibody, cell receptors or nucleic acids. The transducer converts the interaction between the biological component and the sample into a measurable signal which could be an electrical charge, an optical signal, a heat exchanger or some other quantifiable event. In recent years, electrochemical sensors based on continuous potentiometric or amperometric detection of enzyme reaction products have been favoured in the development of biosensors. This is because electrochemical transducers are cheap, rapid to use and portable.

Biosensing Techniques↗
PubMed1991

[Biosensors and clinical analysis].

The determination of organic compounds in blood is important in clinical analysis. Most analysis of organic compounds are based on spectrometric methods. However, these methods involve complicated procedures and require a long time for the reaction to occur. Bioelectrochemical sensors employing immobilized biocatalysts have definite advantages. For medical purposes, miniaturization of enzyme sensors is essential. Miniaturized and highly selective enzyme sensors have been developed by combining enzyme immobilization techniques with silicon technologies. Glucose measurement in blood is the most important and essential assay in the clinical field. For this purpose, we have developed various micro biosensors for glucose measurements. Generally, enzymatic determination of glucose is based on the following reaction (s); (formula; see text) According to the above equation, 4 different micro-glucose sensors were developed; 1) a sensor based on the measurement of produced hydrogen peroxide, 2) a sensor based on the measurement of consumed oxygen, 3) a sensor based on the measurement of enthalpy change during the enzymatic reaction, 4) a sensor based on the measurement of the amount of proton produced, and 5) a sensor based on the measurement of the light emission during enzymatic reaction. For these purposes, various kinds of transducers were used. A micro-hydrogen peroxide electrode, a micro-oxygen electrode, a thermistor, an ISFET (ion selective field effect transistor), and a photon counter. The determination of antibodies, or antigens is also very important in clinical analysis. Several types of immuno-sensors have been developed for these purposes. Considering the integration of immuno-sensors, the miniaturization of immuno-sensors is also required. This review deals with our current study on micro-biosensors for clinical analysis.

Biosensing Techniques↗
PubMedDate not supplied

[Biosensors and their applications (review of the literature)].

Different biosensors (potentiometric, voltampermetric, thermometric, optoelectronic, acoustoelectronic) are reviewed, and the main principles of their operation are discussed. Data on biosensor applications are systematized.

Biosensing Techniques↗
PubMed1987

Review of medical biosensors and associated materials problems.

Developers of biosensors as medical devices are using emerging technologies that incorporate chemical assays with fiber optics and semiconductors. These biosensors will eventually become indwelling catheters for monitoring blood analyte concentrations as well as functioning as controlled feedback elements for artificial organs. Materials used in these devices are subject to problems of manufacture and reliability as well as those induced by the human body's response to these "foreign agents." The Division of Mechanics and Materials Science in the Center for Devices and Radiological Health at the Food and Drug Administration has initiated a program to investigate factors that effect sensitivity, selectivity and reliability of sensors used in biological applications. Our group's principle focus is on sensors of chemical processes. This article is an outgrowth of our research efforts and is a review of some of the technologies that are currently available or becoming available for these applications. The goal of our research is to identify factors that will have an impact on the reliability of long-term implanted medical devices with particular attention to sensors used in feedback-controlled therapeutic systems.

Artificial Organs↗
PubMedDate not supplied

Fiberoptic biosensors in artificial organs.

A large variety of assay methods based on optical principles can be miniaturized and adapted for use as in vivo monitors with the currently available optical fiber technology. Especially exciting is the capability of adapting the selectivity of immunoassays to continuous on-line biosensors by the use of hollow dialysis fibers. Thus, one can envision biosensors that could have many different applications in artificial organ development, from passive systemic monitoring to active feedback control devices for drug delivery.

Artificial Organs↗
PubMed1989

Luminescence biosensors.

A novel optical biosensor for homogeneous immunoassay has been developed on the basis of the finding that electrochemical luminescence of pyrene-labelled antigen is extremely inhibited by immunochemical complexation. Electrochemical luminescence homogeneous immunoassay for human serum albumin (HSA), as a model analyte, was performed with a platinum plate electrode which was located in the vicinity of an optical fibre tip. HSA was determined in the concentration range of 3-25 X 10(-6) mol/l. To improve electrochemical luminescence measurement an optical fibre electrode has been developed by fabricating a transparent platinum film on the top of an optical fibre. The minimum detectable limit of luminol was 10(-11) mol/l with the optical fibre electrode. Luminol was applied as a label for homogeneous immunoassay.

Biosensing Techniques↗
PubMed1989

Stable-light-emitting Escherichia coli as a biosensor.

We have studied possibilities for constructing Escherichia coli strains capable of producing stable light. Light production in E. coli is achieved by cloning the genes encoding bacterial luciferase from Vibrio harveyi. To gain the advantage of sensitive detection of light we transferred the genes under the control of a strong, regulatable promoter system. Stabilization of light produced by E. coli clones was accomplished by finding the optimal plasmid construction and growth conditions as well as suitable measuring buffers. The adjustment of the luciferase synthesis for bioluminescence measurements to a high but not harmful level gives healthy cells and stable luciferase. Cultivation at 30 degrees C in an uninduced state was found to be the most important factor in getting stable-light production. The overall cell metabolism being unstressed gives us the possibility of monitoring cell physiology and factors affecting it via bioluminescence reactions in vivo. To make the results easy to interpret the light emission has to be stable during a measurement period of one to several hours. In the case of the original light-producing bacteria, Vibrio and Photobacterium strains it has not thus far been possible to find conditions where light emission would be stable for several hours. Based on our findings an automated biosensor system can be developed to monitor the effects of biologically active compounds against stable-light-producing bacteria.

Biosensing Techniques↗
PubMedDate not supplied

Fibre-optic biosensor based on luminescence and immobilized enzymes: microdetermination of sorbitol, ethanol and oxaloacetate.

We have investigated highly selective and ultrasensitive biosensors based on luminescent enzyme systems linked to optical transducers. A fibre-optic sensor with immobilized enzymes was designed; the solid-phase bioreagent was maintained in close contact contact with the tip of a glass fibre bundle connected to the photomultiplier tube of a luminometer. A bacterial luminescence fibre-optic sensor was used for the microdetermination of NADH. Various NAD(P)-dependent enzymes, sorbitol dehydrogenase, alcohol dehydrogenase and malate dehydrogenase, were co-immobilized on preactivated polyamide membranes with the bacterial system and used for the microdetermination of sorbitol, ethanol and oxaloacetate at the nanomolar level with a good precision.

Biosensing Techniques↗
PubMed1988

Development of membrane-based biosensors: measurement of current from photocycling bacteriorhodopsin on patch clamp electrodes.

Our initial work toward developing membrane protein-based biosensors has involved use of bacteriorhodopsin (BR) as a model membrane protein. BR was incorporated into liposomes of a polymerizable lecithin, and was shown to pump protons in response to illumination both before and after polymerization of the lipids. In the work described in this paper, BR was first reincorporated in liposomes of asolectin by consonication with purple membrane. The liposomes, which sustained the function of the protein, were used to form a monolayer at the air-water interface. This monolayer was transferred as a bilayer onto patch electrode. When illuminated with a pulse of 514.5-nm light the lipid/protein patch produced a current spike into the pipette corresponding to events no later than the generation of the 412-nm intermediate, probably caused by pumping of protons across the patch membrane. The experiment demonstrates not only the extreme sensitivity of amperometric detection, but also a small tendency for membrane proteins to preferentially orient in this configuration.

Bacteriorhodopsins↗
PubMed1986

[Biosensors].

By the combination of transducers (thermistors, selective electrodes, field-effect transistors, optical systems) with immobilized enzymes or antibodies specific sensors for biologically relevant substances are obtained. The construction, ranges, of linearity, response times and stability of biosensors are demonstrated. Examples are given for their application in clinical analysis and fermentation control. Finally limits and future possibilities are discussed.

Antibodies↗
PubMed1990

Lactate and glucose electrochemical biosensors for the evaluation of the aerobic and anaerobic threshold in runners.

Lactate and glucose are measured in whole blood of athletes running on a treadmill by using two extracorporeal electrochemical biosensors. The lactate sensor was fixed to an endocrine artificial pancreas (Betalike) which had been used in previous extracorporeal experiments. The lactate sensor gave a signal which resulted in a well defined curve that allowed the evaluation of the aerobic as well as the anaerobic threshold. The results obtained with the glucose sensor supported the theory that muscle anaerobic glycolysis is dependent on muscle glycogen rather than on blood glucose.

Adult↗
PubMed1992

Glucose biosensor using glucose oxidase immobilized in polyaniline.

A biosensor for glucose utilizing kinetics of glucose oxidase (EC 1.1.3.4.) was developed. The enzyme was immobilized on polyaniline by covalent bonding, using glutaraldehyde as a bifunctional agent. The system showed a linear response up to 2.2 mM of glucose with a response time of 2.5-4.0 min. In addition, the immobilized enzyme had a higher activity between pH 6.5 and 7.5. The system retained 50% of its activity after 30 d of daily use. The optical absorption spectra of the polyaniline/glucose oxidase electrode after glucose had been added to the buffer solution showed that the absorption band around 800 nm had changed considerably when glucose was allowed to react with the electrode. This optical variation makes polyaniline a very promising polymer for use as a support in optical sensor for clinical application.

Aniline Compounds↗
PubMedDate not supplied

Ascorbic acid biosensor using ascorbate oxidase immobilized on alkylamine glass beads.

A biosensor for ascorbic acid based on enzyme kinetics of ascorbate oxidase (E.C.1.10.3.3) was developed. The enzyme was extracted from Cucurbita maxima, or jerimun and immobilized by covalent bounding, using glutaradehyde as a bifunctional agent, on alkylamine glass beads, with and without enzyme active site protection. A low-cost, home-made oxygen electrode was applied as a transducer. The system has sensitivity from 62.5 up to 500 microM of ascorbic acid with satisfactory operation for more than 2 mo.

Alkylation↗
PubMed1990

A fiberoptic cholesterol biosensor with an oxygen optrode as the transducer.

A biosensor for the continuous optical determination of cholesterol is presented. Cholesterol oxidase is immobilized covalently on a nylon membrane and the consumption of oxygen is measured by following, via fiberoptic bundles, the changes in fluorescence of an oxygen-sensitive dye whose fluorescence is dynamically quenched by molecular oxygen. The dye is dissolved in a very thin silicone membrane placed beneath the enzyme layer. During interaction of the enzyme with cholesterol, oxygen is consumed, which is indicated by the fluorescent dye. At pH 7.25, the analytical range of the sensor is 0.2 to 3 mM and the time to reach a full steady state in a flowing solution ranges from 7 to 12 min.

Biosensing Techniques↗
PubMed1992

Detection of Clostridium botulinum toxin A using a fiber optic-based biosensor.

A rapid, sensitive, analytical method for the detection of Clostridium botulinum toxin has been developed. The fiber optic-based biosensor utilizes the evanescent wave of a tapered optical fiber for signal discrimination. A 50 mW argon-ion laser, which generates laser light at 514 nm, is used in conjunction with an optical fiber probe that is tapered at the distal end. Antibodies specific for C. botulinum are covalently attached to the surface of the tapered fiber. The principle of the system is a sandwich immunoassay using rhodamine-labeled polyclonal anti-toxin A immunoglobin G (IgG) antibodies for generation of the specific fluorescent signal. Various anti-toxin antibodies were immobilized to the fibers. Affinity-purified polyclonal horse anti-toxin A antibodies performed better than the IgG fraction from the same horse serum or than the monoclonal anti-toxin A antibody BA11-3. Botulinum toxin could be detected within a minute, at concentrations as low as 5 ng/ml. The reaction was highly specific and no response was observed against tetanus toxin.

Animals↗