Biomedical subjects

Azmi Telefoncu

Publications and source records attributed to Azmi Telefoncu.

18 recordsLinked to original sources

PubMed2006

Electrical wiring of Pseudomonas putida and Pseudomonas fluorescens with osmium redox polymers.

Two different flexible osmium redox polymers; poly(1-vinylimidazole)12-[Os-(4,4'-dimethyl-2,2'-di'pyridyl)2Cl2](2+/+) (osmium redox polymer I) and poly(vinylpyridine)-[Os-(N,N'-methylated-2,2'-biimidazole)3](2+/3+) (osmium redox polymer II) were investigated for their ability to efficiently "wire" Pseudomonas putida ATCC 126633 and Pseudomonas fluorescens (P. putida DSM 6521), which are well-known phenol degrading organisms, when entrapped onto cysteamine modified gold electrodes. The two Os-polymers differ in redox potential and the length of the side chains, where the Os(2+/3+)-functionalities are located. The bacterial cells were adapted to grow in the presence of phenol as the sole source of organic carbon. The performance of the redox polymers as mediators was investigated for making microbial sensors. The analytical characteristics of the microbial sensors were evaluated for determination of catechol, phenol and glucose as substrates in both batch analysis and flow analysis mode.

2,2'-Dipyridyl↗

PubMed2006

Graphite epoxy composite electrodes modified with bacterial cells.

The modification of a graphite-epoxy composite electrode (GECE) with bacterial cells along with an analytical application are presented. Pseudomonas putida DSM 50026 was used as a biological component and the measurement was based on the respiratory activity of the cells. The optimization of working conditions of resulting biosensor (including pH and temperature) was conducted and the limit of detection was calculated as 7 microM phenol based on the signal to noise ratio. Then the system was applied for xenobiotic detection. Resulting sample signals were found to be very similar with the standard solutions having the same concentration while the recoveries of the spiked samples were close to 100%.

Biosensing Techniques↗

PubMed2006

Effects of mediators on the laccase biosensor response in paracetamol detection.

An enzyme electrode suitable for paracetamol detection was developed by immobilizing laccase on a dissolved-oxygen probe surface. The immobilization procedure was achieved by means of gelatin, which was then cross-linked with glutaraldehyde. The measurement was based on the detection of oxygen consumption in relation to analyte oxidation. The optimum experimental conditions for the biosensor were investigated and the system was calibrated for paracetamol. Also the effects of three different mediators, namely HBT (1-hydroxybenzotriazole), VLA [violuric acid (5-isonitrosobarbituric acid)] and TEMPO (2,2',6,6'-tetramethylpiperidine-N-oxyl radical) were tested for the biosensor's response. As a result, it was observed that HBT has a remarkable effect on the signal by providing more oxygen consumption during the enzymatic reaction. A linear relationship between sensor responses and analyte concentrations was obtained over the concentration range 2.0-15.0 microM, whereas, in the presence of the mediator HBT, this range became 0.5-3.0 microM.

Acetaminophen↗

PubMed2006

Immobilization of pancreatic lipase on chitin and chitosan.

In this study, porcine pancreatic lipase (EC 3.1.1.3) was immobilized on chitin and chitosan by adsorption and subsequent crosslinking with glutaraldehyde, which was added before (conjugation) or after (crosslinking) washing unbound proteins. Conjugation proved to be the better method for both supports. The properties of free and immobilized enzymes were also investigated and compared. The results showed that the pH optimum was shifted from 8.5 to 9.0 for both the immobilized enzymes. Also, the optimum temperature was shifted from 30 to 40 degrees C for chitin-enzyme and to 45 degrees C for chitosan-enzyme conjugates. The immobilization efficiency is low, but the immobilized enzymes have good reusability and stability (storage and operational). Besides these properties, the immobilized lipases were also suitable for catalyzing esterification reactions of fatty acids and fatty alcohols, both with a medium chain length. According to our results, esterification activities of immobilized lipases were two- and four-fold higher for chitosan- and chitin-enzyme, than for the free enzyme, respectively. The immobilization procedure shows a great potential for commercial applications of the immobilized lipase, a relatively low cost commercial enzyme.

Animals↗

PubMed2005

A sensitive determination of dopamine in the presence of ascorbic acid using a nafion-coated clinoptilolite-modified carbon paste electrode.

A selective dopamine determination using a nafion-coated clinoptilolite-modified carbon paste electrode in the presence of ascorbic acid was studied. Both cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV) were used for measurements of dopamine. To improve the selectivity of the clinoptilolite-modified carbon paste electrode in presence of a high concentration of ascorbic acid, the electrode surface was coated with nafion membrane. Experimental parameters affecting the determination of dopamine, including the clinoptilolite ratio, nafion membrane thickness, preconcentration time, preconcentration solution pH, stripping solution pH and interferences are discussed. The developed sensor has a wide linear range, a low detection limit, and good stability and reproducibility. The sensor offers a good alternative to existing analytical methods for dopamine, permits a relatively short analysis time, and is simple, selective and inexpensive.

Ascorbic Acid↗

PubMed2005

Laccase biosensors based on mercury thin film electrode.

A biosensor was developed by immobilizing laccase onto mercury thin film electrode (MTFE) by means of gelatin that is then crosslinked with glutaraldehyde. Mercury thin film (MTF) was deposited onto glassy carbon electrode (GCE) and the obtained biosensor was utilized for the determination of phenolic compounds. The measurement was based on the amperometric detection of oxygen consumption in relation to analyte oxidation. The optimum experimental conditions for the biosensor were investigated and the system was calibrated for both catechol and phenol. A linear relationship between sensor responses and analyte concentrations was obtained in concentration range between 0.5 x 10(-6)-5.0 x 10(-6)M for catechol and 2.5 x 10(-6)-2.0 x 10(-6)M for phenol, respectively. Mercury thin film was also formed onto the surface of screen printed graphite electrodes and applied for the catechol detection. The linearity was observed in concentration range between 2.5 x 10(-6)-3.0 x 10(-5)M.

Biosensing Techniques↗

PubMed2005

Modification of porcine pancreatic lipase with Z-proline.

Porcine pancreatic lipase was modified with Z-proline via the constitution of amide bonds between the free amino groups of lipase and the carboxyl groups of Z-proline, which were activated by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC). Different amounts of Z-proline were bound to lipase. Modification degree was determined by 2,4,6-trinitrobenzene sulphonic acid (TNBS), by means of the decrease in free amino groups on lipase. The reason for choosing Z-proline was its unique structural characteristics, protected amino groups, and its effect on protein conformation by reducing the flexibility of the lipase molecule, thus achieving stabilization against changes in pH and temperature. After the modification, porcine pancreatic lipase was found to have new physicochemical characteristics, such as optimum alkaline pH stability and thermal stability at elevated temperatures.

Animals↗

PubMed2005

Immobilization of alpha-glucosidase in chitosan coated polygalacturonic acid.

Crude alpha-glucosidase from Baker's yeast was immobilized in polygalacturonic acid beads and coated with chitosan. Chemical and physical characterization were performed by using p-nitrophenyl-alpha-D-glucopyranoside (pNPG) as an artificial substrate. Operation, thermal, pH, and strorage stabilities of the free and immobilized enzyme were also examined. The stabilities of immobilized enzyme were found to be better than that of the free enzyme. Furthermore, the hydrolysis rate of the chitosan coated alpha-glucosidase polygalacturonic acid beads were studied. In conclusion, the enzyme beads appear to have good characteristics and offer the prospect that this system may find application in enzyme immobilization, in addition to controlled drug release studies.

Chitosan↗

PubMed2004

Immobilized jerusalem artichoke (Helianthus tuberosus) tissue electrode for phenol detection.

A tissue based biosensor for the determination of phenol was developed by using Jerusalem artichoke (Helianthus tuberosus) in combination with a dissolved oxygen (DO) probe. The tissue electrode response depends linearly on phenol concentration between 0.002 and 0.0101 microM in 10 min response time. Maximum electrode response was found in phosphate buffer at pH 8.0 and 35 degrees C. The reproducibility of the enzyme electrode was also tested by using standard phenol solutions (0.005 microM). The standard deviation (SD) and variation coefficient (cv) were calculated as +/- 1.4 x 10(-4) microM and 3.1%, respectively.

Biosensing Techniques↗

PubMed2004

Acetylcholinesterase (AChE) electrodes based on gelatin and chitosan matrices for the pesticide detection.

Enzyme electrodes for the determination of organophosphate pesticides were developed by using acetylcholinesterase (AChE) in combination with a pH electrode. AChE was immobilized on the surface of pH electrode by using gelatin and chitosan membranes, respectively. The measurement system is based on potentiometric detection of the inhibiting properties of organophosphates on enzyme activity. The phosphate buffer (2.5mM, pH 8.0) and the borate buffer (2.5mM, pH 8.5) at 25 degrees C were established as providing the optimum conditions for the gelatin and chitosan based biosensor systems, respectively. Furthermore, operational, thermal, and organic phase stabilities were also tested. Linear ranges for different organophosphates such as malathion, parathion-methyl, and methamidophos were detected by using both types of biosensor system. Moreover, as well as accuracy, the regeneration conditions by using pyridine-2-aldoximethiodide (PAM-2) as a reactivating agent for the inhibited electrodes were also investigated.

Acetylcholinesterase↗

PubMed2004

Covalent attachment of oligonucleotides to cellulose acetate membranes.

During the last decade, DNA has become an increasingly important biomolecule in several areas. DNA technology has found many applications, e.g., in forensic science, environmental studies, diagnosis and archeometry. DNA microarrays and DNA biosensors applying the principle of immobilization of oligonucleotide on solid supports are used in these areas. DNA immobilization can be performed by adsorption and covalent attachment. In this study cellulose acetate was used as a solid support for oligonucleotide immobilization. Cellulose acetate was activated with 1,1'-Carbonyldiimidazole (CDI) and then coupled with 1,6-hexanediamine (HDA) as a linker. A hexadecadesoxy oligonucleotide was also activated by I-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and immobilized on the membrane by coupling via amino groups. The effects of various parameters on the immobilization oligonucleotide were investigated.

Cellulose↗

PubMed2004

Preparation and properties of lipases immobilized on different supports.

Porcine pancreatic lipase and Candida cylindracea lipase were immobilized on Celite and Amberlite IRA-938. Activities and stabilities of immobilized lipases were investigated. The immobilized lipase derivatives on Celite exhibited grater residual activity and more resistance to thermal inactivation than their immobilized counterpart on Amberlite IRA-938. The apparent optimum temperatures of the immobilized lipases were 7-10 degrees C higher than that of the free enzymes. The native lipase and lipases immobilized on Celite showed same behaviors of pH dependence. But the pH optimum values for lipases immobilized on Amberlite IRA-938 were shifted to the acidic region relative to that of free enzymes. The stabilities of free and immobilized lipases were also investigated.

Animals↗

PubMed2004

Immobilization of lipases on different carriers and their use in synthesis of pentyl isovalerates.

Porcine pancreatic lipase (PPL) and Candida cylindracea lipase (CCL) were immobilized on Celite and Amberlite IRA 938 by deposition from the aqueous solution by the addition of hexane. The influence of the immobilization on the activities of the immobilized lipase derivatives has been studied. The immobilized lipases were used in synthesis of pentyl isovalerates. Various reaction parameters affecting the synthesis of pentyl isovalerates were investigated. The reaction rates were compared with the rates of esterification with free lipases. The immobilized lipases were found to be very effective in the esterification reaction. The lipases immobilized on Celite 545 exhibited better operational stabilities than that of immobilized on Amberlite IRA-938.

Animals↗

PubMed2003

Comparison of chitin and Amberlite IRA-938 for alpha-galactosidase immobilization.

Watermelon alpha-galactosidase (EC 3.2.1.22) was immobilized on a natural (chitin) and a synthetic anion-exchange (Amberlite IRA-938) support by covalent coupling methods. The procedure entails the activation of supports with 1,1'-carbonyldiimidazole (CDI), followed by immobilization of the enzyme on to these supports without and with a spacer arm; gamma-aminobutyric acid (GABA). Optimization of activation was performed by changing the CDI concentrations and coupling efficiencies. The comparison of two immobilization techniques for both chitin and Amberlite IRA-938 was made by comparing different enzyme concentrations against enzyme activity yield. Furthermore, the storage stability of the immobilized enzymes was also investigated and chitin immobilized alpha-galactosidase was found to be better. Although the activity yield of immobilized enzymes were the same for both supports, the short storage stability of immobilized enzyme on Amberlite IRA-938 is currently a drawback to its applications.

Anion Exchange Resins↗

PubMed2003

An enzyme electrode based on lipoxygenase immobilized in gelatin for selective determination of essential fatty acids.

An enzyme electrode for the specific determination of omega-3 and omega-6 fatty acids from the mixture of essential fatty acids (EFAs) was developed by using lipoxygenase (LOX) (EC 1.13.11.12) from soy beans in combination with a dissolved oxygen (DO) probe. The enzyme electrode showed different sensitivities for linoleic (LA) and alpha-linolenic acids (ALA), the most common essential fatty acids. Enzyme electrode response depends linearly on LA concentration between 12.8-160.5 microM and ALA concentration between 3.8-18.9 microM in borate buffer, 0.2 M at pH 9.0. However, in phosphate buffer 0.2 M at pH 6.0 linearity is in the range of 7.5-22.5 microM of ALA concentration at 5 minutes response times. Moreover, maximum electrode response was found in borate buffer at pH 9.0 and 30 degrees C.

Biosensing Techniques↗

PubMed2003

Preparation and properties of alpha-galactosidase chemically attached to activated chitin.

alpha-Galactosidase (alpha-D-galactoside galactohydrolase, EC 3.2.1.22) from watermelon was covalently immobilized on chitin. The immobilized alpha-galactosidase exhibited an activity of 0.61 U per g of carrier and an activity yield of 67%. The properties of free and immobilized alpha-galactosidase were also searched and compared. The results showed that, optimum conditions for activity were not affected by immobilization. The optimum pH and temperature for free and immobilized enzyme found as pH 6.0 and 65 degress C, respectively. Compared with the free enzyme, the temperature and pH stabilities of the immobilized enzyme were similar. Both the enzymes were stable between pH 2-10 and below 50 degrees C. The Km values for free and immobilized enzyme were determined using p-nitrophenyl-alpha-D-galactopyranoside (PNPG) and raffinose as substrates. Operational stability of the immobilized enzyme was investigated by using both substrates. The operational half-life (t 1/2) was calculated as 34 h for PNPG and 28 h for raffinose. The immobilized alpha-galactosidase was also utilized in the hydrolysis of raffinose. The immobilization procedure on chitin was cheap and also easy to carry out, and the immobilized enzyme had good properties that the potential for practical application is considerable.

Chitin↗

PubMed2003

Arginine selective biosensor based on arginase-urease immobilized in gelatin.

Arginase and urease enzymes were immobilized on the surface of pH electrode by using gelatin membrane which is then cross-linked with glutaraldehyde. Sensor response was maximum when 2.5 mM, Tris-HCl buffer (pH 8.5) was used at 25 degrees C. The biosensor response depends linearly on arginine concentration between 0.025-0.310 mM with response time 10 min. Furthermore, application of the system for the arginine detection in serum samples was also tested.

Arginase↗

PubMed2003

Immobilization of phospholipase A2 on porous glass and its application for lowering serum cholesterol concentration.

Phospholipase A2 (PLA2; EC 3.1.1.4) is a lipolytic enzyme that hydrolysis the ester bond in sn-2 position of phospholipids. In this work, the PLA2 from hog pancreas was covalently coupled to porous glass. The properties of free and immobilized enzyme were also investigated and compared. The optimum pH and temperature were found as 8.5 and 50 degrees C, respectively for both free and immobilized enzyme. The immobilized enzyme had good properties that potential for medical application is considerable. Its use in lowering plasma cholesterol concentrations in blood samples was also demonstrated.

Animals↗