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PubMed1989

Transducer mechanisms for optical biosensors. Part 2: Transducer design.

Optical fibre biosensors basically require two components, namely optical fibres, to enable remote measurements to be made, and immobilised reagents. The propagation of light along fibres is discussed and various effects causing attenuation and a fall in transmission efficiency, viz. coupling of light into the fibre and attenuation characteristics of the fibre itself, are considered. The modes of interaction of electromagnetic radiation with the immobilised reagent, viz. absorption alone, absorption followed by luminescence, reflection, or scattering, are discussed and followed by methods by which these effects can be utilised to provide an optically detectable signal. Practical sensor configurations are described and the associated optical instrumentation is outlined. Finally a brief overview is presented of the current state of the art of these sensors.

Blood Chemical Analysis↗

PubMed1986

Can biosensors help to protect drinking water?

A large proportion of drinking water is abstracted for treatment from lowland rivers--about 30% in the UK--and this water is at particular risk from sudden and poisonous industrial or agricultural pollution. To cover the range of potential pollutants it may be possible to use biosensors as broadband monitors for toxins. The underlying assumption is that some biological processes, when challenged with a toxin, will be affected in a way analogous to that of man, and that therefore on-line scrutiny of such processes will provide early warning of substances liable to be detrimental to human health. Suitable processes for study might involve multi-cellular organisms, whole cells or enzymes. To date, most practical work has concentrated on fish, but enzymes and single cells hold out the promise of quicker response and, possibly, easier maintenance.

Animals↗

PubMed1995

A highly stable and selective biosensor using modified nicotinic acetylcholine receptor (nAChR).

Methods for developing stable, sensitive and selective bilayer lipid membrane (BLM)-based biosensors are discussed. Stable BLMs were formed over micromachined polyimide apertures. Selective sensors were made by incorporating nicotinic acetylcholine receptors (nAChRs) modified with bispecific antibodies (BsAbs). When two BsAbs, attached to one nAChR, encounter antigen (Ag), channels are blocked. Sensitivity to single Ag molecules would be possible by monitoring closure of individual nAChRs.

Animals↗

PubMed1992

Characterization of the effects of aluminum on luciferase biosensors for the detection of ecotoxicity.

Luciferase-based biosensors are becoming increasingly used for environmental monitoring. A transcriptional fusion of the Vibrio harveyi luxAB genes (encoding bacterial luciferase) to the fliC gene of Escherichia coli was constructed and luminescence shown to be induced (in liquid media) in the presence of 1-10 micrograms/ml aluminum, but not copper, iron or nickel. Moreover, luminescence is markedly increased at pH 5.5, where aluminum is more soluble than at pH 7.0. However, aluminum also stimulated luciferase activity when the luxAB genes were located in the xyl operon. This suggests that aluminum stimulates luciferase enzyme activity in vivo. These results are specific to E. coli, as no such aluminum stimulation was observed in the luminescent bacterium V. harveyi. These results have important implications in the generalized use of these clones for environmental monitoring, where aluminum can be present at elevated concentrations.

Aluminum↗

PubMed1992

Construction and use of two alpha-human atrial natriuretic peptide-fragment affinity chromatography columns in the isolation of C- and N-terminal epitope-specific antibodies for use in a prototype alpha-hANP biosensor.

Two alpha-human atrial natriuretic peptide (alpha-hANP) based affinity chromatography columns were produced by covalently immobilizing the C- and N-terminal epitopes of alpha-hANP. The stationary phase was made from a controlled-pore-glass bead solid support, which was silanized and treated with sulphosuccinimidyl 4-(maleimidomethyl)cyclohexyl carboxylate before the individual fragments were immobilized by substitution at their thiol groups. These columns were used to isolate alpha-hANP-specific antibodies from a goat anti-alpha-hANP serum, which were then further sorted according to their epitope specifity. These C- and N-terminal epitope-specific antibodies were in turn used as components in the construction of an alpha-hANP biosensor based on an enzyme-linked immunosorbent assay (ELISA) sandwich principle. Initial in vitro testing of the sensor using a physiological alpha-hANP solution showed a reproducible response to the peptide. There is to date no other equally fast, sensitive and precise method available to detect this peptide. This alpha-hANP sensor may prove to be an invaluable aid in human medicine as a monitor of patient status during transplant surgery, for example, an area inaccessible to radioimmunoassay and normal ELISA techniques.

Amino Acid Sequence↗

PubMed1989

Extracorporeal determination of glucose, lactate and potassium with electrochemical biosensors.

Glucose, lactate and potassium ions have been continuously measured in whole blood by using two extracorporeal electrochemical biosensors and a new flow through potassium electrode. For experiments involving the "glucose clamp", lactate and potassium electrodes have been connected in series to an endocrine artificial pancreas "Betalike" properly modified. The same artificial pancreas has been used in experiments measuring the anaerobic threshold (AT) by continuous monitoring of lactate in athletes. In this case glucose and lactate sensors were connected in series for continuous measurement of both metabolites in blood in real time. The results are in agreement with the biochemical pathways involving such metabolites.

Adult↗

PubMed1990

Fish scales as biosensors for catecholamines.

Certain fish scales contain specialized cells (chromatophores) with pigment granulas, which can be dispersed or aggregated in the cells. The degree of aggregation is determined by a transmitter substance, noradrenaline, released by the sympathetic nerve endings in the skin. Isolated scales from, for example, cuckoo wrasse (Labrus ossifagus) retain a large sensitivity to externally applied noradrenaline (or more generally catecholamines) for several weeks. The degree of aggregation in isolated scales can be measured objectively by simple photometric techniques. We demonstrate in this paper how fish scales can be used to monitor catecholamine levels in human blood plasma. A discussion of other potential biosensor applications of this intact biological receptor-effector system is also given.

Animals↗

PubMed1991

Biosensors based on membrane transport proteins.

We propose a novel class of biosensors based on membrane bound receptors or transport proteins as the sensing element. The protein is incorporated in a planar lipid bilayer which covers the transducer. The transducer may detect an electric current, a voltage, or a change in fluorescence. A prototype lactose sensor is presented which consists of a quartz slide covered by a lipid membrane containing the protein lactose permease from Escherichia coli. This protein is a lactose/H+ cotransporter, hence lactose in the external medium initiates lactose/H+ cotransport across the lipid membrane. This leads to a rise in proton concentration in the small volume between the lipid membrane and the quartz surface which can be detected by a pH-sensitive fluorescence dye.

Arylsulfonates↗

PubMed1991

Effects of receptor concentration, media pH and storage on nicotinic receptor-transmitted signal in a fiber-optic biosensor.

The optical signal generated by a nicotinic acetylcholine receptor (nAChR)-based optical biosensor was dependent on the density of toxin binding sites (i.e. receptors) immobilized on the surface of the fiber. The maximum density of nAChR receptors absorbed on the optic fibers, measured using [125I]-alpha-bungarotoxin (the alpha-neurotoxin of the Bungarus snake venom) binding, was 6.2 pmol of receptor sites per fiber. Incubation time, that was required for maximal noncovalent immobilization of the receptor protein on the fiber, was less than 10 min. Immobilization of the nAChR protein on the quartz fiber was affected by pH of the medium, with pH 3.5 as the optimal. Stored in phosphate buffered saline (PBS) or in a dry nitrogen atmosphere, the nAChR optical sensor showed no loss of activity over the first 3 days, then showed a slow but gradual loss in activity (45% over the next 30 days).

Animals↗

PubMed1991

Formation of a bilayer lipid membrane on rigid supports: an approach to BLM-based biosensors.

Sensory transduction in living cells is thought to involve a change of electrical parameters at the receptor membrane following specific binding events at the membrane surface. Because of the complexity of the biomembrane structure and the environmental factors associated with it, experimental bilayer lipid membranes (BLMs) have been employed for elucidation of processes at the membrane level. This is because the BLM system can be easily probed by a host of powerful and sensitive electrochemical methods. Further, recent advances in microelectronics and biotechnology suggest that the development of a BLM-based electrochemical biosensor may be possible. This paper describes the use of bilayer lipid membranes on solid substrates for analysis of sensor development problems, with relevance to a possible novel type of biomolecular device. Some electrical parameters of the new structure were measured and compared to usual BLM results. The advantages of the self-assembled structure, together with the measuring system, are discussed in terms of stability and sensitivity.

Biosensing Techniques↗

PubMed1991

Application of cell culture toxicity tests to the development of implantable biosensors.

Cell culture toxicity testing methods were modified and applied to the development of implantable glucose microsensors, and positive and negative control materials suitable for the microsensor assessment were established. The location, source and degree of the toxic effect in a multi-component biosensor was spatially visualized with cell monolayers. A freshly prepared sensor showed moderate toxicity, mainly as a result of the presence of glutaraldehyde and the residual solvents in the polymer layers. However, it was possible to reduce the toxicity by removing the leachable toxic substances through extraction in phosphate buffer, and a non-toxic sensor was readily obtained.

Agar↗

PubMed1992

Gene probe assays on a fibre-optic evanescent wave biosensor.

This report describes experiments to detect oligonucleotide hybridization at the surface of a fibre-optic evanescent wave biosensor. Conditions were optimized and the time course of hybridization reactions were found to be very rapid compared to conventional hybridization assays. Binding was easily reversed by heating and the sensor surface could be reused many times. Short (16- and 20-mer) oligonucleotides bound to the waveguide surface could be used to detect fluorescein-labelled complementary sequences at the nanomolar level. Polymerase chain reaction was used to generate a 204-base oligomer that was attached to the waveguide surface. Fluorescein-labelled oligos bound at either the proximal or distal ends of this probe were found to give similar outputs.

Base Sequence↗

PubMed1992

Utilization of biosensors and chemical sensors for space applications.

There will be a need for a wide array of chemical sensors for biomedical experimentation and for the monitoring of water and air recycling processes on Space Station Freedom. The infrequent logistics flights of the Space Shuttle will necessitate onboard analysis. The advantages of biosensors and chemical sensors over conventional analysis onboard spacecraft are manifold. They require less crew time, space, and power. Sample treatment is not needed. Real time or near-real time monitoring is possible, in some cases on a continuous basis. Sensor signals in digitized form can be transmitted to the ground. Types and requirements for chemical sensors to be used in biomedical experimentation and monitoring of water recycling during long-term space missions are discussed.

Aerospace Medicine↗

PubMed1992

Implementation of a thermal biosensor in a process environment: on-line monitoring of penicillin V in production-scale fermentations.

The production of penicillin V was monitored in 0.5 m3 and 160 m3 bioreactors. The thermal biosensor was an enzyme thermistor modified for split-flow analysis. The heat signal generated in the enzyme column was corrected for any nonspecific heat with the use of an identical but inactive reference column. The on-line monitoring was performed in the fermentation pilot plant and in a fermentation plant of Novo Nordisk A/S. Immobilized beta-lactamase was used to monitor three consecutive 0.5 m3 penicillin fermentations. Broth samples were continuously filtered through a tangential flow filtration unit in a sterile external loop. The on-line penicillin V values were 10% higher than those obtained by off-line HPLC analysis. Alternatively a polypropylene filtration probe was inserted into a 160 m3 bioreactor and samples were withdrawn at 0.5 ml/min. The same experiments were repeated with purified and immobilized penicillin V acylase. The on-line penicillin V values obtained with this enzyme correlated very well with those from HPLC analysis. The on-line monitoring was controlled and analysed by a software program written in Labtech Notebook.

Biosensing Techniques↗

PubMed1992

An optical biosensor for lysine based on the use of lysine decarboxylase and a cadaverine-sensitive membrane.

We describe an optical biosensor for lysine based on the use of lysine decarboxylase and an optical transducer for detection of cadaverine which is formed as a result of enzymatic action. A plasticized PVC (polyvinyl chloride) membrane containing a lipophilic tartrate as the amine carrier acts as the optical cadaverine sensor. The transport of the cadaverine cation into the membrane is coupled to a transport of a proton (of the indicator dye) out of the membrane. This causes a spectral change of the indicator dye which can be related to the cadaverine concentration, provided the pH is kept constant. The enzymatic reaction is performed in an enzyme reactor which is part of a flow-through system. The dynamic range is from 0.1 to 100 mM for both cadaverine and lysine. While the cadaverine sensor is moderately selective (ethylamines, for example, interfere), the whole sensor system is highly specific for lysine, nicotine being the only major interferent. Unlike other enzyme-based detection schemes where the production of CO2 (in case of decarboxylases) or consumption of oxygen (in case of oxidases) is measured, this scheme is based on the measurement of the organic ammonium ion (cadaverin cation) formed in the enzymatic reaction. The major advantage of this approach is that in many real samples there is a rather low and fairly constant background of organic amines.(ABSTRACT TRUNCATED AT 250 WORDS)

Biosensing Techniques↗

PubMed1992

Biosensors based on the energy metabolism of living cells: the physical chemistry and cell biology of extracellular acidification.

The silicon microphysiometer is a biosensor-based instrument that detects changes in the physiological state of cultured living cells by monitoring the rate at which the cells excrete acidic products of metabolism. This paper discusses the chemical and biological factors that determine the performance and applications of such a system. Under typical culture conditions, extracellular acidification is dominated by the excretion of lactic and carbonic acids formed during the energy metabolism, using glucose and glutamine as carbon sources. The maintenance of transmembrane ionic gradients is an important use of energy, as is cell growth. The activation of cellular receptors usually causes transient or sustained increases in acidification rate. The energetic cost of generating second messengers is probably too small to account for either change, so events more distal to the receptor-activation process must be responsible. The opening of ion channels may cause the increases in some cases. In others, changes in intracellular pH and loose coupling between ATP hydrolysis and synthesis may be involved; models for these processes are presented.

Acids↗

PubMed1992

Covalent immobilization of avidin on glassy carbon electrodes as the basis for multivalent biosensors.

One of the most crucial steps for the successful construction of a biosensor is the appropriate and reproducible coupling of the biological part (e.g. enzyme, antibody) to the inorganic moiety of the device (e.g. electrode, microchip). In this paper three methods of immobilization of avidin to a glassy carbon electrode are described. Depending on the type of immobilization, avidin may lose its biological activity as determined by an enzyme immunoassay, using biotinylated reagents. If avidin is covalently bound to the glassy carbon electrode via the bridge molecule 4.4'-diaminodiphenylamine, the biological activity is retained. About 1.5 pmol of avidin can be bound to the electrode (3 mm in diameter), resulting in a nearly complete monolayer of protein.

Avidin↗

PubMed1992

Laccase-based biosensor for determination of polyphenols: determination of catechols in tea.

A new method of amperometric determination of phenolic compounds using an enzyme electrode is proposed. The latter represents the combination of the oxygen electrode and immobilized laccase. Analytical systems of flow injection and batch types were considered. A method of immobilization was developed that provided an increase in the stability of the enzyme. Optimal conditions for biosensor operation were found. The time needed for analysis in the flow injection mode was below 100 s. A column with immobilized enzyme could be used for up to 500 determinations of phenolic compounds without decrease of the enzyme activity. The practical validity of the method was demonstrated by tannin analysis in tea of different brands.

Biosensing Techniques↗