Şule Pekyardımcı

Urea Biosensors Based on PVC Membrane Containing Palmitic Acid

A new urea biosensor was prepared by immobilizing urease with four different procedures on poly(vinylchloride) (PVC) ammonium membrane electrode containing palmitic acid by using nonactine as an ammonium-ionophore. The analytical characteristics were investigated and were compared those of the biosensor prepared by using carboxylated PVC. The effect of pH, buffer concentration, temperature, urease concentration, stirring rate and enzyme immobilization procedures on the response to urea of the enzyme electrode were investigated. The linear working range and sensitivity of the biosensor were also determined. The urea biosensor prepared by using the PVC membranes containing palmitic acid showed more effective performance than those of the carboxylated PVC based biosensors. Additionally, urea assay in serum was successfully carried out by using the standard addition method.

Electrochemical DNA biosensor based on poly(2,6-pyridinedicarboxylic acid) modified glassy carbon electrode for the determination of anticancer drug gemcitabine

In this study, a simple methodology was used to develop a new electrochemical DNA biosensor based on poly(2,6-pyridinedicarboxylic acid) (P(PDCA)) modified glassy carbon electrode (GCE). This modified electrode was used to monitor for the electrochemical interaction between the dsDNA and gemcitabine (GEM) for the first time. A decrease in oxidation signals of guanine after the interaction of the dsDNA with the GEM was used as an indicator for the selective determination of the GEM via differential pulse voltammetry (DPV). The guanine oxidation peak currents were linearly proportional to the concentrations of the GEM in the range of 1-30mgL(‒1). Limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.276mgL(‒1) and 0.922mgL(‒1), respectively. The reproducibility, repeatability, and applicability of the analysis to pharmaceutical dosage forms and human serum samples were also examined. In addition to DPV method, UV-vis and viscosity measurements were utilized to propose the interaction mechanism between the GEM and the dsDNA. The novel DNA biosensor could serve for sensitive, accurate and rapid determination of the GEM.

A sensitive electrochemical DNA biosensor for antineoplastic drug 5-fluorouracil based on glassy carbon electrode modified with poly(bromocresol purple)

This paper describes an electrochemical sensor for the first time based on poly(bromocresol purple) (P(BCP)) developed to observe the interaction between 5-fluorouracil (5-FU) and fish sperm double strand DNA (dsDNA). The P(BCP) film was electrosynthesized by cyclic voltammetry method on the glassy carbon electrode (GCE). The dsDNA was electrochemically immobilized on the surface of P(BCP) modified GCE and the DNA biosensor was prepared. The interaction mechanism of dsDNA with 5-FU was investigated by differential pulse voltammetry using this biosensor. A decrease in the guanine oxidation peak current of the biosensor was observed after the interaction of dsDNA and 5-FU in 0.5 mol L(-1) acetate buffer (pH 4.8) containing 0.02 mol L(-1) NaCl. The accumulation time and dsDNA concentration were optimized to obtain the best peak current response. Under optimum conditions, the linear response on the guanine signal decreasing curve was observed in the 5-FU concentration range of 1.0-50 mg L(-1). The interaction mechanism between dsDNA and 5-FU was further investigated by UV-vis spectroscopy and viscometer. The results reveal that intercalation is the primary mode of interaction between 5-FU and dsDNA.

A novel amperometric biosensor based on ZnO nanoparticles-modified carbon paste electrode for determination of glucose in human serum

Abstract Zinc oxide nanoparticles-(ZnONPs)modified carbon paste enzyme electrodes (ZnONPsMCPE) were developed for determination of glucose. The determination of glucose was carried out by oxidation of H2O2 at +0.4 V. ZnONPsMCPE provided biocompatible microenvironment for GOx and necessary pathway of electron transfer between GOx and electrode. The response of GOx/ZnONPsMCPE was proportional to glucose concentration and detection limit was 9.1 × 10–3 mM. Km and Imax, were calculated as 0.124 mM and 2.033 μA. The developed biosensor exhibits high analytical performance with wide linear range (9.1 × 10–3–14.5 mM), selectivity and reproducibility. Serum glucose results allow us to ascertain practical utility of GOx/ZnONPsMCPE biosensor.

A new amperometric carbon paste enzyme electrode for ethanol determination

Abstract In this study, a new amperometric carbon paste enzyme electrode for determination of ethanol was developed. The carbon paste was prepared by mixing alcohol dehydrogenase, its coenzyme nicotinamide adenine dinucleotide (oxidized form, NAD+), poly(vinylferrocene) (PVF) that was used as a mediator, graphite powder and paraffin oil, then the paste was placed into cavity of a glass electrode body. Determination of ethanol was performed by oxidation of nicotinamide adenine dinucleotide (reduced form, NADH) generated enzymatically at +0.7 V. The effects of enzyme, coenzyme and PVF amounts; pH; buffer concentration and temperature were investigated. The linear working range of the enzyme electrode was 4.0×10−4–4.5×10−3 M, determination limit was 3.9×10−4 M and response time was 50 s. The optimum pH, buffer concentration, temperature, and amounts of enzyme, NAD+ and PVF for enzyme electrode were found to be 8.5, 0.10 M, 37°C, 2.0, 6.0, and 12.0 mg, respectively. The storage stability of enzyme electrode at +4°C was 7 days. Enzyme electrode was used for determination of ethanol in two different wine samples and results were in good agreement with those obtained by gas chromatography.

Electrochemical glucose biosensor based on nickel oxide nanoparticle-modified carbon paste electrode

Abstract In the present work, we designed an amperometric glucose biosensor based on nickel oxide nanoparticles (NiONPs)-modified carbon paste electrode. The biosensor was prepared by incorporation of glucose oxidase and NiONPs into a carbon paste matrix. It showed good analytical performances such as high sensitivity (367 μA mmolL–1) and a wide linear response from 1.9 × 10–3 mmolL–1 to 15.0 mmolL–1 with a limit of detection (0.11 μmolL–1). The biosensor was used for the determination of glucose in human serum samples. The results illustrate that NiONPs have enormous potential in the construction of biosensor for determination of glucose.

Potentiometric Glucose Determination in Human Serum Samples with Glucose Oxidase Biosensor Based on Iodide Electrode

Glucose potentiometric biosensor was prepared by immobilizing glucose oxidase on iodide-selective electrode. The hydrogen peroxide formed after the oxidation of glucose catalysed by glucose oxidase (GOD) was oxidized by sodium molybdate (SMo) at iodide electrode in the presence of dichlorometane. The glucose concentration was calculated from the decrease of iodide concentration determined by iodide-selective sensor. The sensitivity of glucose biosensor towards iodide ions and glucose was in the concentration ranges of 1.0 × 10−1–1.0 × 10−6 M and 1.0 × 10−2−1.0 × 10−4 M, respectively. The characterization of proposed glucose biosensor and glucose assay in human serum were also investigated.

Comparison of Covalent and Noncovalent Immobilization of Malatya Apricot Pectinesterase (Prunus armeniaca L.)

Abstract: Pectinesterase isolated from Malatya apricot pulp was noncovalently and covalently immobilized onto bentonite and glutaraldehyde-containing amino group functionalized porous glass beads surface at pH 8.0 and pH 9.0, respectively. The effect of various parameters such as pH, temperature, activation energy, heat and storage stability on immobilized enzyme were investigated. The optimum temperature of covalently and noncovalently immobilized PE was 50°C. This value was 60°C for free PE. Although optimum pH of covalently-immobilized PE was 8.0, this parameter was 9.0 for free and covalently-immobilized PE. The noncovalently immobilized enzyme exhibited better thermostability than the free and covalently immobilized PE.

Fabrication of amperometric cholesterol biosensor based on SnO2 nanoparticles and Nafion-modified carbon paste electrode

This study reports the fabrication of an amperometric cholesterol biosensor based on cholesterol oxidase (ChOx), SnO2NPs and Nafion-modified carbon paste enzyme electrodes (CPE/SnO2NPs-ChOx/Naf). The electrochemical characterisations of BCPE and CPE/SnO2NPs were performed using CV and EIS. The determination of cholesterol was carried out by electrochemical oxidation of H2O2 at 0.6 V vs. Ag/AgCl. The CPE/SnO2NPs-ChOx/Naf presented a linear range from 0.20 μ.mol L−1 to 4.95 μmol L−1 with a low limit of detection (0.04 μ.mol L−1). In addition, the optimal values for pH and temperature were found to be 7.5 and 35°C, respectively. The CPE/SnO2NPs-ChOx/Naf was used for the determination of cholesterol in serum samples and good results were obtained.

Noncovalent Immobilization of Pectinesterase (Prunus armeniaca L.) onto Bentonite

In this work, pectinesterase isolated from Malatya apricot was immobilized onto acid-treated bentonite surface by simple adsorption at pH 9.0. The properties of free and immobilized enzyme were defined. The effect of various factors such as pH, temperature, heat, and storage stability on immobilized enzyme were investigated. Optimum pH and temperature were determined to be 9.0 and 50°C, respectively. Kinetic parameters of the immobilized enzyme (Km and Vmax values) were also determined as 0.51 mM of the Km and 14.6 µmol min−1 mg−1 of the Vmax. No drastic change was observed in the Km value after immobilization. The Vmax value of immobilized enzyme was 8.4-fold bigger than those of free enzyme. Thermal and storage stability experiments were carried out. The patterns of heat stability indicated that the immobilization process tends to stabilize the enzyme. The properties of the immobilized enzyme were compared to those of the free enzyme.