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At least 1,549 records · Page 86Linked to original sources
PubMed1993

Anticholinesterase activity measurement by a choline biosensor: application in water analysis.

A choline amperometric biosensor was assembled and used to measure the anticholinesterase activity due to compounds (which have the property to inhibit cholinesterase enzymes) present in water samples. This parameter can be used as a 'toxicological index', defined as the amount of compound which causes a certain percentage of cholinesterase inhibition equivalent to a known amount of a reference compound causing the same percentage inhibition. The organophosphorus insecticide Paraoxon, which has proved to be a strong inhibitor of cholinesterase enzymes, was chosen as the reference compound. The analysis was carried out by monitoring the decrease of cholinesterase activity in the presence of a pesticide and a substrate specific for the enzyme whose reaction produces choline. The decrease in choline production was measured by the choline sensor and correlated to the concentration of anticholinesterase compound present in the solution. Parameters such as buffer, pH, temperature and incubation time were optimized. The rate constant Ki was calculated experimentally for Paraoxon and used in the anticholinesterase activity measurements at different fixed incubation times. The probe was calibrated with different standard solutions of Paraoxon. The effect of Paraoxon and heavy metals on the choline probe was evaluated. This probe was then used for the determination of anticholinesterase activity of some organophosphorus pesticides, and heavy metals in spiked waters. Samples were also analysed by liquid/liquid extraction and GC determination. Results seem to correlate with acute toxicity expressed as LD50 (oral, rat). Analysis of water samples from different sources in central Italy were analysed for total anticholinesterase activity (TAA) and compared with a reference procedure.

Biosensing Techniques↗
PubMed1993

An activated sludge-based biosensor for rapid IC50 estimation and on-line toxicity monitoring.

The RODTOX (Rapid Oxygen Demand and TOXicity tester), an activated sludge-based respirographic biosensor, is a device for on-line monitoring of the short-term biochemical oxygen demand (stBOD) and potential toxicity of incoming wastewater on the basis of on-line interpretation of respirograms resulting from pulse additions of either calibration substrate or sample. The principle of toxicity detection is based on the comparison of calibration respirograms before and after receiving a potential toxicant. In this paper, the results of the RODTOX as an on-line toxicity monitor are presented. In addition, a simple and fast procedure to estimate the IC50 of a toxicant has been developed, and its validity and good repeatability demonstrated. The performance of this procedure is compared with that of the Microtox test.

Biosensing Techniques↗
PubMed1993

Biosensor for direct determination of glucose and lactate in undiluted biological fluids.

This paper describes the implementation of a bienzyme sensor for the direct determination of glucose and lactate in undiluted biological samples. The biosensor exploits the competitive action versus the substrate itself by two different enzymes immobilized into a sandwich of two different membranes. In this way the quantity of substrate reaching the indicating electrode is reduced and this determines an extension of the linearity range.

Biosensing Techniques↗
PubMed1994

A spectroscopically interrogated flow-through type toxicity biosensor.

A simple immobilised cell biosensor is described which uses the MUVS (Metabolic Ultraviolet Spectroscopy) response as an assay for toxic compounds in water. Bacterial cells are immobilised in an agarose membrane in a flow cell. A sample of water is passed over the flow cell. The UV absorbence of the membrane, compared to a similar membrane lacking bacterial cells, is measured at 200 nm. When the cells are stressed so that their energy metabolism is reduced, their UV spectra change, and specifically their OD200 drops within 15 seconds of exposure to the toxin. The sensor has potential for use in rapid tests, and possibly continuous monitoring, of environmental samples for toxic contamination.

Biosensing Techniques↗
PubMed1994

Fibre-optic biosensor for hypoxanthine and xanthine based on a chemiluminescence reaction.

Fibre-optic biosensors were constructed for determination of hypoxanthine and xanthine. Xanthine oxidase and peroxidase were immobilized on different preactivated membranes which were subsequently mounted onto the tip of a fibre-optic bundle. The H2O2 generated by the reaction of hypoxanthine and xanthine oxidase was measured by chemiluminescence (CL) detection using luminol and peroxidase. A linear calibration curve of the sensors in the range of 1-316 microM hypoxanthine and 3.1-316 microM xanthine, respectively, with a detection limit of 0.55 microM hypoxanthine was obtained. Recovery of hypoxanthine ranged between 91 and 102%.

Biosensing Techniques↗
PubMed1995

Antigen-antibody diffusion-limited binding kinetics of biosensors: a fractal analysis.

A fractal analysis is made of antigen-antibody binding kinetics in various biosensor applications reported in the literature. Both sensor configurations are considered, wherein (a) the antigen is in solution and the antibody is immobilized on the fibre-optic surface, and (b) the antibody is in solution and the antigen is immobilized on the fibre-optic surface. For example, when the antigen is immobilized, an increase in the antibody concentration (anti-Ars) in solution leads to (a) an increase in the fractal dimension value and hence the state of disorder or roughness, and (b) a higher rate coefficient for binding on the fibre-optic surface. An analysis of the influence of different parameters on the fractal dimension values for a particular effect, such as a comparison of fresh and regenerated immunosensors, helps to clarify the conformational states and reactions occurring on the fibre-optic surface. Examination of the different cases presented together provides novel physical insights into the state of disorder or roughness on the surface. This research should contribute towards techniques for manipulating the reactions occurring on fibre-optic surfaces in desired directions.

Antigen-Antibody Reactions↗
PubMed1995

A silicon-based biosensor for real-time toxicity testing in normal versus cancer liver cells.

The potentiometric alternating biosensor (PAB) system has been utilized to monitor the effects on normal versus cancer cells of Mitoxantrone, a potent inhibitor of nucleic acid synthesis commonly utilized in the clinical treatment of hepatocarcinomas. In this first series of toxicity tests, we have utilized a primary culture of rat hepatocytes and a stabilized line named HepG2 from a human hepatoma. Primary cultures of hepatocytes represent a unique tool in toxicology/pharmacology as shown in previous works. A suitable microvolume flow chamber has been designed and produced. The chamber is equipped with inlet and outlet circuits and with a fixed transducer (Si/SiO2/Si3N4 chip) facing a cover slip on which cells grow. The PAB system is here utilized only in the pH-sensitive configuration with a single measuring spot, warranting an accurate determination of the change in the extracellular acidifcation rate resulting from drug administration. We have also observed the changes in the acidification rate of 3T6 mouse fibroblasts, induced by a treatment with Ara-C, a well-known DNA antimetabolite. New insights can be obtained from these studies into the drug response of normal versus cancer cells and into the feasibility of real-time PAB monitoring of drug toxicity and efficacy, towards effective human cancer treatment. The effect of increasing drug concentrations on cellular metabolism is here compared with the results obtained from conventional tests (optical microscopy, Neutral Red and Trypan Blue assays).

Animals↗
PubMed1995

Interface analysis in biosensor design.

In a survey, the analytical tools to characterise and optimise properties and stabilities of interfaces in thin film biosensors are discussed. After an introduction to microscopic and spectroscopic techniques and different transducers, case studies are presented. They concern bioaffinity sensors with particular emphasis on biomimetic recognition structures, catalytic sensors, transmembrane sensors, cell sensors, and the ambitious goal of addressing individual biomolecular function units.

Biosensing Techniques↗
PubMed1996

Microbial biosensor for free fatty acids using an oxygen electrode based on thick film technology.

A microbial biosensor based on thick film technology was developed. The microorganisms, Arthrobacter nicotianae, were immobilized in Ca-alginate directly on the electrode surface. For the stability of the calcium alginate gel the addition of 0.5 mM CaCl2 to the assay buffer was necessary. The respiratory activity of the microorganisms was monitored by oxygen consumption at -600 mV vs. Ag/AgCl reference electrode. The sensor was used in a batch system and was applied to the determination of free fatty acids in milk. Short-chain fatty acids (C4:0-C12:0) were the preferential substrates, with butyric acid being the main substrate. Consequently, the concentration of free short-chain fatty acids was represented as the butyric acid equivalent. The sensor showed linearity over the concentration range 9.5-165.5 microM (correlation coefficient, r = 0.99920). The response time of the sensor was approximately 3 min. No additional dialysis membrane was necessary, which led to a high sensitivity of the sensor and fast response times. Recovery rates of 98-113% were found for butyric acid in milk samples using the sensor without any additional membrane and a sample dilution of 200 by the assay. Two widespread disadvantages of microbial sensors, long response times and long times to return to the baseline signal after use, could be overcome.

Acyl-CoA Oxidase↗
PubMed1996

Bombardier beetle based biosensor.

A biosensor constructed by combining an oxygen electrode with the liquid ejected by bombardier beetles (Pheropsophus aequinoctialis) immobolized on a collagen membrane is developed for hydrogen peroxide. The sensor presents a linear range of 2.0 x 10(-4)-2.0 x 10(-3) M and a reproductibility of approximately 2%. It shows a better lifetime than similar ones employing purified catalase. The selectivity is good since other enzymes are not present in the natural source employed.

Animals↗
PubMed1996

Transduction in microbial biosensors using multiplexed bioluminescence.

The enormous diversity of genetic responses in living microbes to their environment is an attractive resource on which to base biosensor designs. In particular, there is much interest in microbial sensors for environmental monitoring where toxicity can be ascertained directly by its action on cellular physiology. However, due to the complexities of living systems, the utility of genetic-based microbial sensors has been limited by the ability to accurately transduce the activities of specific genetic sensing systems into readily measurable signals. We present here a strategy for employing an additional signal in the sensor design, to provide an internal baseline control upon which to reliably interpret sensor responses. The strategy relies on using beetle luciferases capable of emitting optical signals of different wavelengths; the optical signals are a sensitive real-time indicator of genetic activity within the cells. The different wavelengths allow both a target and control signal to be incorporated into each cell, providing a means of differentiating between specific effects of a genetic sensing system and other non-specific interfering influences.

Bacteria↗
PubMed1996

Multilayer films containing immobilized nucleic acids. Their structure and possibilities in biosensor applications.

Langmuir-Blodgett (LB) and film technologies based on electrostatic attraction self-assembly (SA) are shown to be useful for immobilization of nucleic acids (DNA, polynucleotides) onto solid supports in sensor devices. The nucleic acids were immobilized in complexes with cationic surfactants (for LB) and polycations (for SA). Infrared spectral studies showed that DNA unfolds in multilayer LB films with octadecylamine and conserves its double helical structure in the LB films with dioctadecyldimethylammonium and in the SA films with polyallylamine, polyethylenimine and poly-L-lysine. Atomic groups and the types of interactions determining the complex formation of these films have been identified. The hydration of LB and SA films was studied to find out binding sites of water molecules and to evaluate the flexibility of nucleic acid compounds in the multilayer films. The possibilities of biosensor applications of these LB and SA films were monitored on binding of specific reagents for DNA by DNA-containing films and mononucleotides by a complementary single-stranded polynucleotide immobilized on a positively charged solid support.

Biosensing Techniques↗
PubMed1992

Biosensors and flow injection analysis.

Combining flow injection analysis with a biosensor is a novel biosensing process which has allowed speedy and accurate analysis. Diagnostic analysis is the most important application for biosensing flow injection analysis, but other applications include bioprocess monitoring, analysis of food and agricultural products, as well as environmental analysis. In addition, the analysis of compounds, such as explosives and abused drugs, and monitoring of Salmonella, the microorganism that causes food poisoning, have been reported.

Animals↗
PubMed2003

Monitoring of the heat-shock response in Escherichia coli using an optical biosensor.

A surface plasmon resonance (SPR) method for monitoring the concentration of the chaperone DnaK and its relation to physiological stress response in a recombinant Escherichia coli strain subjected to heat shock is described. The DnaK protein, an abundantly occurring representative of the heat-shock proteins, was used as a marker of physiological stress. The SPR biosensor instrument was used for label-free immunoaffinity detection directly in cell culture lysates using an anti-DnaK monoclonal IgG antibody immobilized on the sensor surface. The SPR method provides a fast response (<8 min) and a reproducible (RSD<2%), accurate (comparison to the direct enzyme-linked immunosorbent assay), and sensitive (LOD<1 nM) assay for determination of the DnaK level in cell culture lysates. The operational stability of the method was high compared to that of other SPR assays; the sensitivity decreased at only 2.7%/h. This allowed measurement of more than 220 samples per sensor surface. Storage stability was determined at 25 degrees C (100% after 17 h) and 10 degrees C (101% after 1 month). The method was validated by standard additions of DnaK (30, 60, and 120 nM) with recovery indices in the range 95.7-103.7%.

Biochemistry↗
PubMed2004

Tuning the redox and enzymatic activity of glucose oxidase in layered organic films and its application in glucose biosensors.

Glucose oxidase was embedded in organic films through a layer-by-layer approach, where the enzyme demonstrated significantly enhanced electron-transfer reactivity and finely tuned enzymatic activity. An unmediated, reagentless glucose biosensor was accordingly prepared with two polyethylenimine/glucose oxidase bilayers-modified pyrolytic graphite electrode. A calibration linear range of glucose was 0.5-8.9 mM with a detection limit of 50 microM and sensitivity of 0.76 microA mM(-1).

Aspergillus niger↗
PubMed2004

Carbon nanotube aqueous sol-gel composites: enzyme-friendly platforms for the development of stable biosensors.

A new type of composite material based on carbon nanotubes and an aqueous sol-gel process has been developed. The electrochemical characteristics of these composites were investigated and compared to composites made with an alkoxy silane sol-gel process. The use of carbon nanotubes, as the conductive part of the composite, facilitated fast electron transfer rates. The feasibility of this type of composite for the development of biosensors was demonstrated using l-amino acid oxidase. The stability of the enzyme was increased when it was encapsulated in the aqueous sol-gel, and the sensor retained more that 50% of its response after 1 month of testing.

Biosensing Techniques↗
PubMed2004

Analyte-receptor binding on surface plasmon resonance biosensors: a fractal analysis of Cre-loxP interactions and the influence of Cl, O, and S on drug-liposome interactions.

A fractal analysis of the association and dissociation (whereever applicable) of Cre-loxP interactions and drug-liposome interactions on a sensor chip surface is presented. In both of these cases a dual-fractal analysis is required to adequately describe the association kinetics. The dissociation kinetics for Cre-loxP interactions is adequately described by a single-fractal analysis. The dual-fractal analysis used to describe the association kinetics of Cre-loxP interactions is consistent with the original two-step mechanism presented using a surface plasmon resonance biosensor. Our analysis includes both diffusion and surface effects by introducing the fractal dimension which makes quantitative the degree of heterogeneity on the sensor chip surface. Affinities are provided. Only the association kinetics were analysed for drug-liposome interactions since the initial sections of the dissociation curves were too steep to obtain reasonable drug-liposome complex concentration values on the sensor chip with time. Attempts made to relate the association rate coefficients with the molecular weight of the drug were unsuccessful. On using desipramine and imipramine as "arbitrarily selected standards" or "references" (only C, H, and N atoms present), it was noticed from the data analysed that the inclusion of the O and S atoms in the drug leads to a decrease in the association rate coefficients, ka1 (or k1) and ka2 (or k2) (compared with the arbitrarily selected standards or references). Similarly, the addition of the Cl atom in the drug leads to an increase in the association rate coefficient (compared with the arbitrarily selected standards or references). More data needs to be analysed to determine whether this is true for other drugs also.

Chlorine↗