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At least 667 records · Page 37Linked to original sources

PubMed2002

A portable toxicity biosensor using freeze-dried recombinant bioluminescent bacteria.

A portable biosensor has been developed to meet the demands of field toxicity analysis. This biosensor consists of three parts, a freeze-dried biosensing strain within a vial, a small light-proof test chamber, and an optic-fiber connected between the sample chamber and a luminometer. Various genetically engineered bioluminescent bacteria were freeze-dried to measure different types of toxicity based upon their modes of action. GC2 (lac::luxCDABE), a constitutively bioluminescent strain, was used to monitor the general toxicity of samples through a decrease in its bioluminescence, while specific toxicity was detected through the use of strains such as DPD2540 (fabA::luxCDABE), TV1061 (grpE::luxCDABE), DPD2794 (recA::luxCDABE), and DPD2511 (katG::luxCDABE). These inducible strains show an increase in bioluminescence under specific stressful conditions, i.e. membrane-, protein-, DNA-, and oxidative-stress, respectively. The toxicity of a sample could be detected by measuring the bioluminescence 30 min after addition to the freeze-dried strains. In an attempt to enhance the sensitivity of the freeze-dried cells, glucose and Tween 80 were tested as additives. It was found that the addition of glucose had a negative effect on the viability of the freeze-dried cells, while samples having Tween 80 showed an increase in their viability. On the other hand, the addition of either Tween 80 or glucose decreased the final bioluminescent response of DPD2540 in response to 4-chlorophenol. Using these strains, many different chemicals were tested and characterized. This portable biosensor, with a very simple protocol, can be used for field sample analysis and the monitoring of various water systems on-site.

Biosensing Techniques↗

PubMed2002

A glucose biosensor based on microporous polyacrylonitrile synthesized by single rare-earth catalyst.

A glucose biosensor was constructed by electrochemical adsorption of glucose oxidase (GOD) in microporous polyacrylonitrile (PAN), which was synthesized by single rare-earth catalyst-Y(OAr)(3.) The biosensor shows a fast response, good operational stability and reproducibility. The influences of molecular weight of polymer, pH, operating potential and temperature on the biosensor response were explored by amperometric method. The apparent activation energy and optimum pH of enzyme-catalyzed reaction are 35.9 kJ mol(-1) and 6.2, respectively.

Acrylic Resins↗

PubMed2002

Stabilized lipid film based biosensor for atenolol.

This work reports a technique for the stabilization after storage in air of a lipid film based biosensor for atenolol. Microporous filters composed of glass fibers (nominal pore sizes 0.7 and 1.0 microm) were used as supports for the formation and stabilization of these devices. The lipid film is formed on the filter by polymerization prior to its use. Methacrylic acid was the functional monomer, ethylene glycol dimethacrylate was the crosslinker and 2,2'-azobis-(2-methylpropionitrile) was the initiator. The method for preparation of stabilized lipid film biosensor is studied throughout this work. The response towards atenolol of these stabilized lipid membrane biosensor, for repetitive use, composed of phosphatidylcholine was compared with planar freely suspended bilayer lipid membranes (BLMs). The stabilized lipid membranes provided similar artificial ion gating events as BLMs in the form of transient signals and can function for repetitive uses after storage in air. This will allow the practical use of the techniques for chemical sensing based on lipid films and commercialization of these devices.

Atenolol↗

PubMed2002

Biosensors for in vivo glucose measurement: can we cross the experimental stage.

The development of in vivo working glucose sensors needs two decades, so far. The availability of long term functional implantable biosensors for continuous glucose measurings is a basic prerequisite for the individualized optimum insulin treatment of diabetics. Enzymatic electrochemical sensors are described which realize a functional stability over more than 2 years in vitro, however their function in vivo is limited due to certain bioincompatibility expressed by inflammation of the surrounding tissue, exudates, and immun reactions. The paper reflects an overview concerning different sensor covering materials used as more or less suitable diffusion membranes. From experimental studies in animals and human volunteers conclusions are drawn for further developmental steps of biosensors for in vivo use and for the applicability of glucose sensors for transient diagnostic purposes and as a basis for glucose controlled therapeutic measures. The results demonstrate that further progress aimed at long term biostability of implanted biosensors needs to solve technological problems and the serial production of sensors with really comparable qualities as a prerequisite for clinical trials.

Biosensing Techniques↗

PubMed2002

Development, validation, and application of an acetylcholinesterase-biosensor test for the direct detection of insecticide residues in infant food.

A highly sensitive and rapid food-screening test based on disposable screen-printed biosensors was developed, which is suitable for monitoring infant food. The exposure of infants and children to neurotoxic organophosphates and carbamates is of particular concern because of their higher susceptibility to adverse effects. The European Union has, therefore, set a very low limit for pesticides in infant food, which must not contain concentrations exceeding 10 microg/kg for any given pesticide. The maximum residue limit (MRL) has been set to be near the determination threshold that is typically achieved for pesticides with traditional analytical methods. The biosensor method could detect levels lower than 5 microg/kg and thus clearly fulfills the demands of the EU. To substantiate these measurements, recovery rates were determined and amounted on average to 104% in food. Matrix effects were eliminated by the introduction of a special electrode treatment. The test was compared with two traditional pesticide multiresidue analysis methods (GC-MS, LC-MS) using 26 fruit and vegetable samples from local markets and 23 samples of processed infant food from Germany, Spain, Poland and USA. Three infant food samples exceeded the MRL of 10 microg/kg when analyzed by either biosensor test or multiresidue methods.

Acetylcholinesterase↗

PubMed2003

Amperometric hydrogen peroxide biosensor with sol-gel/chitosan network-like film as immobilization matrix.

A new type of sol-gel/organic hybrid composite material based on the cross-linking of natural polymer chitosan with (3-aoryloxypropyl) dimethoxymethylsilane was developed for the fabrication of an amperometric H(2)O(2) biosensor. The composite film was used to immobilize horseradish peroxidase (HRP) on a gold disk electrode. The properties of sol-gel/chitosan and sol-gel/chitosan-HRP films have been carefully characterized by atomic force microscopy and Fourier transform infrared. By using fluorescent label, a protein density on sol-gel/chitosan has been calculated to be 3.14 x 10(12) moleculescm(-2). With the aid of catechol mediator, the biosensor had a fast response of less than 2 s with linear range of 5.0 x 10(-9)-1.0 x 10(-7) mol l(-1) and a detection limit of 2 x 10(-9) mol l(-1). Its current response shows a typical Michaelis-Menten mechanism. The apparent Michaelis-Menten constant K(M)(app) is found to be 1.30 micromol l(-1). The activation energy for enzymatic reaction is calculated to be 8.22 kJ mol(-1). The biosensor retained approximately 75% of its original activity after about 60 days of storage in a phosphate buffer at 4 degrees C.

Biosensing Techniques↗

PubMed2003

Flow injection amperometric detection of OP nerve agents based on an organophosphorus-hydrolase biosensor detector.

A flow-injection system with an organophosphorus-hydrolase (OPH)-biosensor detector has been developed and characterized for the rapid detection of organophosphorus (OP) nerve agents. The enzyme was immobilized onto a thin-film gold detector through a cystamine-glutaraldehyde coupling. Factors influencing the performance were optimized. The resulting flow system offered a fast, sensitive, selective, and stable response. The peak current increased linearly with the concentration of paraoxon and methyl parathion over the 1-10 microM range (sensitivity, 2.29 and 1.04 nA/microM, respectively). The OPH-biosensor flow injection systems offered low detection limits (e.g. 0.1 microM paraoxon), along with a good precision (R.S.D. of 3.6% for 20 successive injections of a 1.0 microM paraoxon solution). The OPH-biosensor flow detector offers great promise for rapid field screening of OP pesticides and nerve agents.

Aryldialkylphosphatase↗

PubMed2003

Reactivities of organic phase biosensors: 6. Square-wave and differential pulse studies of genetically engineered cytochrome P450(cam) (CYP101) bioelectrodes in selected solvents.

Cytochrome P450(cam) (CYP101) bioelectrodes suitable for application in organic phases were prepared from genetically engineered CYP101 and vesicular dispersions of didodecyldimethylammonium bromide. The amperometric biosensor system was characterised under anaerobic conditions by cyclic and square-wave voltammetric methods. Cyclic- and square-wave-voltammetry studies showed that the biosensors exhibited direct reversible electron transfer between the haem iron atom and the glassy carbon electrode surface. The formal redox potential estimated for the electrode in acetonitrile was -380 mV/Ag-AgCl. The formal potential shifted anodically as the organic phase biosensor responded irreversibly to substrate (camphor) under anaerobic and aerobic conditions in acetonitrile. Differential pulse analysis of the reactivities of the CYP101 enzyme electrode confirmed the square-wave voltammetry result, which showed that the binding of substrate decreased the redox potential necessary for initiating the monooxygenation reaction of cytochrome P450(cam).

Adamantane↗

PubMed2003

Amperometric determination of choline released from rat submandibular gland acinar cells using a choline oxidase biosensor.

A choline (CHO) biosensor based on the determination of H(2)O(2) generated at the electrode surface by the enzyme choline oxidase (CHOx) was developed. The biosensor consisted of CHOx retained onto a horseradish peroxidase (HRP) immobilized solid carbon paste electrode (sCPE). The HRPsCPE contained the molecule phenothiazine as redox mediator and CHOx was physically retained on the electrode surface using a dialysis membrane. Several parameters have been studied such as, mediator amount, influence of applied potential, etc. The CHO measurements were performed in 0.1 M phosphate buffer, pH 7.4. Amperometric detection of CHO was realized at an applied potential of 0.0 mV vs Ag/AgCl. The response is linear over the concentration range 5.0x10(-7)-7.0x10(-5) M, with a detection limit of 1.0x10(-7) M. This biosensor was used to detect choline released from phosphatidylcholine (PC) by phospholipase D (PLD) in isolated rat salivary gland cells stimulated by a purinergic agonist (ATP).

Adenosine Triphosphate↗

PubMed2003

A fractal analysis of protein to DNA binding kinetics using biosensors.

A fractal analysis of a confirmative nature only is presented for the binding of estrogen receptor (ER) in solution to its corresponding DNA (estrogen response element, ERE) immobilized on a sensor chip surface [J. Biol. Chem. 272 (1997) 11384], and for the cooperative binding of human 1,25-dihydroxyvitamin D(3) receptor (VDR) to DNA with the 9-cis-retinoic acid receptor (RXR) [Biochemistry 35 (1996) 3309]. Ligands were also used to modulate the first reaction. Data taken from the literature may be modeled by using a single- or a dual-fractal analysis. Relationships are presented for the binding rate coefficient as a function of either the analyte concentration in solution or the fractal dimension that exists on the biosensor surface. The binding rate expressions developed exhibit a wide range of dependence on the degree of heterogeneity that exists on the surface, ranging from sensitive (order of dependence equal to 1.202) to very sensitive (order of dependence equal to 12.239). In general, the binding rate coefficient increases as the degree of heterogeneity or the fractal dimension of the surface increases. The predictive relationships presented provide further physical insights into the reactions occurring on the biosensor surface. Even though these reactions are occurring on the biosensor surface, the relationships presented should assist in understanding and in possibly manipulating the reactions occurring on cellular surfaces.

Biosensing Techniques↗

PubMed2003

Sol-gel-derived titanium oxide/copolymer composite based glucose biosensor.

A new type of sol-gel-derived titanium oxide/copolymer composite material was developed and used for the construction of glucose biosensor. The composite material merged the best properties of the inorganic species, titanium oxide and the organic copolymer, poly(vinyl alcohol) grafting 4-vinylpyridine (PVA-g-PVP). The glucose oxidase entrapped in the composite matrix retained its bioactivity. Morphologies of the composite-modified electrode and the enzyme electrode were characterized with a scanning electron microscope. The dependence of the current responses on enzyme-loading and pH was studied. The response time of the biosensor was < 20 s and the linear range was up to 9 microM with a sensitivity of 405 nA/microM. The biosensor was stable for at least 1 month. In addition, the tetrathiafulvalene-mediated enzyme electrode was constructed for the decrease of detection potential and the effect of three common physiological sources that might interfere was also investigated.

Adsorption↗

PubMed2003

Co-immobilized microbial biosensor for BOD estimation based on sol-gel derived composite material.

A novel type of biochemical oxygen demand (BOD) biosensor was developed for water monitor, based on co-immobilizing of Trichosporon cutaneum and Bacillus subtilis in the sol-gel derived composite material which is composed of silica and the grafting copolymer of poly (vinyl alcohol) and 4-vinylpyridine (PVA-g-P(4-VP)). Factors that influence the performance of the resulting biosensor were examined. The biodegradable substrate spectrum could be expanded by the co-immobilized microorganisms. The biosensor prepared also exhibited good reproducibility and long-term stability. Good agreement was obtained between the results of the sensor BOD measurement and those obtained from conventional BOD(5) method for water samples.

Bacillus subtilis↗

PubMed2003

Rapid and convenient determination of oxalic acid employing a novel oxalate biosensor based on oxalate oxidase and SIRE technology.

A new method for rapid determination of oxalic acid was developed using oxalate oxidase and a biosensor based on SIRE (sensors based on injection of the recognition element) technology. The method was selective, simple, fast, and cheap compared with other present detection systems for oxalate. The total analysis time for each assay was 2-9 min. A linear range was observed between 0 and 5 mM when the reaction conditions were 30 degrees C and 60 s. The linear range and upper limit for concentration determination could be increased to 25 mM by shortening the reaction time. The lower limit of detection in standard solutions, 20 microM, could be achieved by means of modification of the reaction conditions, namely increasing the temperature and the reaction time. The biosensor method was compared with a conventional commercially available colorimetric method with respect to the determination of oxalic acid in urine samples. The urine oxalic acid concentrations determined with the biosensor method correlated well (R=0.952) with the colorimetric method.

Biosensing Techniques↗

PubMed2003

Optical biosensor for simultaneous detection of captan and organophosphorus compounds.

The optical biosensor consisting of GST and acetylcholinesterase (AChE)-immobilized gel film was developed to detect captan and organophosphorus compounds simultaneously in contaminated water. The sensing scheme was based on the measurement of decrease of products formation (s-(2,4-dinitrobenzene) glutathione and alpha-naphthol by GST and AChE, respectively) due to the inhibition by captan and organophosphorus compounds. The absorbance of s-(2,4-dinitrobenzene) glutathione and alpha-naphthol was detected at 400 and 500 nm, respectively, by a proposed optical biosensor system. It was observed that AChE was inhibited by both captan and organophosphorus compounds, and GST was inhibited only by captan. The simultaneous detection and quantification of captan and organophosphorus compounds could be successfully achieved by the proposed sensor system. The proposed biosensor could successfully detect the captan and organophosphorus compounds concentration from 0 to 2 ppm.

Acetylcholinesterase↗

PubMed2003

Hydrogen peroxide biosensor based on microperoxidase-11 entrapped in lipid membrane.

A highly catalytic activity microperoxidase-11 (MP-11) biosensor for H(2)O(2) was developed to immobilizing the heme peptide in didodecyldimethylammonium bromide (DDAB) lipid membrane. The enzyme electrode thus obtained responded to H(2)O(2) without electron mediator or promoter, at a potential of +0.10 V versus Agmid R:AgCl. A linear calibration curve is obtained over the range from 2.0 x 10(-5) to 2.4 x 10(-3) M. The biosensor responds to hydrogen peroxide in 15 s and has a detection limit of 8 x 10(-7) M (S/N=3) Providing a natural environment with lipid membrane for protein immobilization and maintenance of protein functions is a suitable option for the design of biosensors.

Biosensing Techniques↗

PubMed2003

Vascularizing the tissue surrounding a model biosensor: how localized is the effect of a subcutaneous infusion of vascular endothelial growth factor (VEGF)?

Implantable continuous biosensors would improve disease management but long term function of such devices have been limited by a hypovascular foreign body capsule that inhibits influx of analytes. To assess whether capsule vascularity could be increased, we studied the histologic effects of a 28-day continuous infusion of vascular endothelial growth factor (VEGF) (0.45 microg/day) vs. saline from the surface of a model disk biosensor that was implanted subcutaneously in rats. At day 40, tissue was obtained at varying distances from the infusion port and capsular microvessels were counted using two histologic techniques. VEGF treatment led to a marked increase in capillary density. In tissue located 1 mm away from the infusion site, capillary density in VEGF-treated animals was 200-300% higher than in saline controls. Tissue located 13 mm away, but not 25 mm away, also demonstrated neovascularization. Serum obtained from a distant vein during the infusion did not show an elevated concentration of VEGF. These data demonstrate that a subcutaneous infusion of VEGF creates localized neovascularization of the foreign body capsule and suggest that systemic effects of VEGF are avoidable. Vascularization of a foreign body capsule surrounding a subcutaneous biosensor might well extend its useful life.

Animals↗

PubMed2004

Miniaturized pH biosensors based on electrochemically modified electrodes with biocompatible polymers.

Potentiometric pH sensors based on linear polyethylenimine (L-PEI) and linear polypropylenimine(L-PPI), two synthetic enzymes and biocompatible polymers, films were prepared by electropolymerization of three different monomers: ethylenediamine (EDA), 1,3-diaminopropane (1,3-DAP) and diethylenetriamine (DETA) in order to be used in clinical, dermatological and biological applications, such as in vivo analysis. In a first step a biosensor was tested which consisted in a platinum wire protruded from glass sheath. The polymer film coated on these platinum electrodes showed good linear potentiometric responses to pH changes from pH 3 to 10. Resulting electrodes present both good reversibility and good stability versus time. The effect of the different polymer film thicknesses to potentiometric responses was also studied. This study allowed us to develop a miniaturized pH biosensor in the second step. This sensor was fabricated using photo-lithography, followed by sputtering and lift-off processes, and it included an electronic detection system. We have also successfully studied the potentiometric responses to pH changes of this device over a period of 1 month, and so we propose this new pH micro-biosensor as an alternative to classical pH sensors currently used in dermatology.

Biocompatible Materials↗

PubMed2004

Novel biosensor chip for simultaneous detection of DNA-carcinogen adducts with low-temperature fluorescence.

A monoclonal antibody (MAb)-gold biosensor chip with low-temperature laser-induced fluorescence detection for analysis of DNA-carcinogen adducts is described. Optimization of the detection limit, dynamic range, and biosensing applicability of the MAb-gold biosensor chip was achieved by: (1) using dithiobis(succinimidyl propionate (DSP)) as a protein linker and (2) employing recombinant protein A to provide oriented immobilization of the MAbs. The use of DSP, which has a short methylene chain length, led to faster protein binding kinetics and higher protein surface density than a longer dithiobis(succinimidyl undecanoate) (DSU) linker. The incorporation of recombinant protein A increased the distance between the oriented MAb-bound analytes and the gold surface. The increased distance minimized fluorescence quenching, resulting in about a 10-fold increase in the fluorescence signal in comparison with a chip without protein A. The improved chip architecture was used to demonstrate that biosensing of two structurally similar benzo[a]pyrene (BP)-derived DNA adducts, BP-6-N7Gua and BP-diolepoxide-10-N2dG, bound to two specific MAbs immobilized from a mixture at the same address on the chip, is feasible. These mutagenic adducts are formed by one-electron oxidation and monooxygenation pathways, and are depurinating and stable DNA adducts, respectively. It is shown that the DNA adducts can be easily identified at the same address using time-resolved, low-temperature laser-based fluorescence spectroscopy. The current limit of detection is in the low femtomole range. These results indicate that a single biosensor chip consisting of a Au/DSP/protein A/MAb nano-assembly, with analyte-specific MAbs and low-temperature fluorescence detection should be suitable for simultaneous detection and quantitation of the above adducts, as well as the luminescent antigens for which selective MAbs exist.

Benzo(a)pyrene↗