1,720,969 research outputs found
Glucose oxidase/hexokinase electrode for the determination of ATP
No full textA hydrogen peroxide based enzyme electrode for the determination of ATP has been developed by the immobilization of glucose oxidase and hexokinase. Competition between the enzymes for the substrate glucose allowed the measurement of ATP. Different immobilization procedures and different types of hexokinase have been tested. Using a BSA-glutaraldehyde procedure and hexokinase from an overproducing strain of bakers' yeast, ATP was measured in the 0.05-0.5 mmol l(-1) range with a detection limit of 0.01 mmol l(-1). ATP concentrations comparable to those reported in the literature and a good recovery were obtained when the enzyme electrode was used with human erythrocyte hemolysate.[...
Amperometric bienzymic sensor for aspartame
No full textAn amperometric enzyme electrode for the determination of aspartame was developed by covalent immobilization of alcohol oxidase and a-chymotrypsin, A platinum based hydrogen peroxide electrode was used as the detector, Excellent sensitivity was obtained using batch, flow-through and flow injection methods with detection limits of 2 x 10(-7), 4 x 10(-7) and 10(-6) mol l(-1), respectively, Different strategies for eliminating interfering compounds, including the introduction of an additional alcohol oxidase-catalase membrane and signal subtraction using an alcohol electrode, were employed, A recovery study on seven food samples was carried out and the results were satisfactory.[...
Demonstration of labeless detection of food pathogens using electrochemical redox probe and screen printed gold electrodes
No full textThe demonstration of a labeless immunosensor for the detection of pathogenic bacteria using screen printed gold electrodes (SPGEs) and a potassium hexacyanoferrate(II) redox probe is reported. Gold electrodes were produced using screen printing and the gold surfaces were modified by a thiol based self assembled monolayer (SAM) to facilitate antibody immobilisation. SAMs based on the use of thioctic acid (TA), mercaptopropionic acid (MPA) and mercaptoundecanoic acid (MUA) were evaluated. Following antibody immobilisation via the optimum SAM, the redox behaviour and diffusion co-efficient (D) of the potassium hexacyanoferrate(II) probe was monitored in the absence and presence of analyte. In the presence of analyte, a change in the apparent diffusion co-efficient of the redox probe was observed, attributable to impedance of the diffusion of redox electrons to the electrode surface due to the formation of the antibody-bacteria immunocomplex. No change in the diffusion co-efficient was observed when a non-specific antibody (mouse IgG) was immobilised and antigen added. The system has been demonstrated with Listeria monocytogenes and Bacillus cereus. (C) 2002 Elsevier Science B.V. All rights reserved
Rapid amperometric determination of magnesium(II) ions
No full textAn amperometric procedure for the measurement of magnesium(II) has been developed using the enzyme hexokinase in solution and glucose oxidase immobilized onto a preactivated polymeric support. The reaction of hexokinase was monitored following the decrease in current due to the glucose consumption by the enzyme in the presence of the ATP-Mg2+ complex. The reaction rate was dependent on the concentration of magnesium(II) in solution. Concentrations of hexokinase and ATP were optimised. Measuring the current change in the 1-3 min interval after the start of the reaction magnesium(II) can be determined in the 4 x 10(-5) to 10(-3) M range. Other divalent cations tested showed no interference. The magnesium(II) content of 5 pharmaceutical products was measured with the amperometric and compared to a spectrophotometric procedure. The results correlated well.[...
Human cytomegalovirus detection by a quartz crystal microbalance immunosensor
No full textA piezoelectric affinity sensor has been developed to detect distinctive antigens of the human cytomegalovirus. Either the specific antibodies or the antigen were immobilized on the gold electrode. To develop a rapid immunoassay, various assay formats were tested in relation with the different antigen composition. First, a direct assay was carried out immobilizing the specific antibody on the crystal surface by passive adsorption. Next, Protein A, thiol/polyL-lysine mixed self-assembled monolayers were tested as methods of gold modification. A competitive format was exploited by immobilization of the antigen onto the crystal activated by SAM and polyL-lysine. This procedure yielded a preliminary calibration curve. A linear range between 2.5 and 5 μg/ml of gB epitope in solution and a detection limit of 1 μg/ml were measure
Colorimetric microarray detection system for Ghrelin Using Aptamer-Technology
No full textThe aim of this research was to compare the efficiency in term of miniaturization, multiplexing, reproducibility and sensitivity of colorimetric microarray versus an enzyme linked oligonucleotide assay (ELONA). A competition assay was performed to explore the complex formation between 5 '-biotin NOX-B11, a special aptamer called spiegelmer, and ghrelin, a growth hormone releasing acylated peptide from stomach. The aptamer technology is a very powerful method suitable for large-scale synthesis and overcoming the disadvantages of antibodies (unstable, expensive to produce, and so on) while remaining as efficient as antibodies in binding to the target. The aptamer used in this work was based on spiegelmer oligonucleotides approach that has been considered as one of the simplest, most straightforward, and cost-effective method to develop artificial receptors.[...
AN AMPEROMETRIC NADH BIOSENSOR BASED ON NADH OXIDASE FROM THERMUS-AQUATICUS
No full textA biosensor for the determination of the reduced cofactor nicotinammide adenine dinucleotide (NADH) has been developed using the enzyme NADH oxidase from Thermus aquaticus immobilized on an Immobilon AV membrane. A hydrogen peroxide electrode,was used as the detection system. The NADH electrode showed a monotonous response with near linearity in the 5.10(-7) to 2.10(-5) M range, with a detection limit of 2.10(-7) M. Analytical parameters such as pH, response time and lifetime,vere characterized. The probe showed no change in sensitivity between pH 4.5 and 9.5 and retained 70% of its initial activity after 50 days of storage in buffer. A method for the measurement of lactic dehydrogenase (LDH) activity was developed using the biosensor. The response was linear in the 10-1000 U l(-1) range. The addition of NADH and LDH to serum gave recovery values between 94 and 107%. The determination of LDH in two control sera and in three serum samples was performed with a standard spectrophotometric procedure and the biosensor. The results correlated well.[...
ALCOHOL ELECTRODES IN BEVERAGE MEASUREMENTS
No full textAn alcohol electrode which had been optimized(1) to give an extended linear response to alcohol, eliminate the classical electrochemical interferences of hydrogen peroxide-based electrodes and be pH independent, was used to measure the alcohol concentration in beverage samples both in batch and FIA (wall jet) mode. The results obtained were compared to a spectrophotometric measurement used with a Sigma kit. It was found that the batch measurements were more accurate than the kit and FIA, although very good precision could be obtained with FIA. The method is rapid, easy to perform and requires no sample preparation.[...
A lactoperoxidase-based flow injection amperometric biosensor for iodide detection
No full textThe following contains work carried out into the preparation of an amperometric enzymatic biosensor (M.P. Byfield, R.A. Abuknesha, Biochemical aspects of biosensors. Biosens. Bioelectron. 9 (1994) 373-400; C.R. Lowe, An introduction to the concepts and technology of biosensors. Biosensors 1 (1985) 3-16; J.S. Schultz, Biosensors. Sci. Am. 8 1991 48-55) using the enzyme, lactoperoxidase (LPOD), for the detection of iodide. In this paper, a study of two major avenues which were undertaken to achieve an iodide biosensor, using electrochemical transduction techniques, are discussed. The first of these focuses on the use of LPOD in solution using both DPBS and acetate buffers, while later work has concentrated on investigations into the immobilised enzyme. The former has been shown to measure iodide concentrations of less than 0.1 mu mol/l while the latter can be used to detect iodide levels lower than 10 mu mol/l. The difficulties and drawbacks associated with both these systems are discussed. (C) 1998 Elsevier Science S.A. All rights reserved.[...
Screening of rationally-designed oligopeptides for Listeria monocytogenes detection by means of high density colorimetric microarray
No full textThe aim of this work was to optimize, by means of molecular modeling software, biomimetic-based traps for pathogen detection suitable for analytical applications like screening or pre-analytical methods. The pathogen prototype system chosen was Listeria monocytogenes because of the large number of X ray and NMR structures available. 298 oligopeptides were computationally designed mimicking the binding pocket of the mammalian protein E-cadherin, the target of Listeria monocytogenes adhesion, internalin A. The contribution of individual peptides to bind was investigated using FRED, a protein-ligand docking program. Ten peptides were selected for experimental analysis taking as selection parameters the length, the position in the docking pocket and the score of simulated binding energy. A series of competition assays were carried out using high density colorimetric microarray using various bacteria species (Listeria monocytogenes, Listeria monocytogenes genetically modified without internalin A, Listeria innocua and Lactococcus lactis) in solution with computationally selected peptides. The data demonstrated that peptides could be able to distinguish Listeria monocytogenes with an EC50 up to 10(7)cfu x mL(-1). In particular the peptide with the best calculated binding score gave the highest statistically unambiguous response toward Listeria monocytogenes compared to other bacteria, demonstrating that rationally simulated approach can be useful as preliminary screening in the choice of biomimetic ligands.[...
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