Pınar Esra Erden

A review of enzymatic uric acid biosensors based on amperometric detection.

This review summarizes the studies carried on the development of amperometric uric acid biosensors over the past twenty years. Sensing principles, enzyme immobilization techniques, the electrode types, different approaches and various matrices used for biosensor fabrication are presented along with their benefits and limitations. Uric acid biosensors based on different modes of transducing devices such as optical, potentiometric, conductometric are also referred.

Electrochemical biosensing of galactose based on carbon materials: graphene versus multi-walled carbon nanotubes

In this study, two enzyme electrodes based on graphene (GR), Co3O4 nanoparticles and chitosan (CS) or multi-walled carbon nanotubes (MWCNTs), Co3O4 nanoparticles, and CS, were fabricated as novel biosensing platforms for galactose determination, and their performances were compared. Galactose oxidase (GaOx) was immobilized onto the electrode surfaces by crosslinking with glutaraldehyde. Optimum working conditions of the biosensors were investigated and the analytical performance of the biosensors was compared with respect to detection limit, linearity, repeatability, and stability. The MWCNTs-based galactose biosensor provided about 1.6-fold higher sensitivity than its graphene counterpart. Moreover, the linear working range and detection limit of the MWCNTs-based galactose biosensor was superior to the graphene-modified biosensor. The successful application of the purposed biosensors for galactose biosensing in human serum samples was also investigated.

An amperometric enzyme electrode for creatine determination prepared by the immobilization of creatinase and sarcosine oxidase in poly(vinylferrocenium).

A new enzyme electrode for the determination of creatine was developed by immobilizing creatinase (CI) and sarcosine oxidase (SO). The enzymes were co-immobilized in a poly(vinylferrocenium) matrix onto the surface of a platinum working electrode. Crosslinking with glutaraldehyte (GA) and bovine serum albumin (BSA) was selected as the best immobilization method for the enzymatic system. Determination of creatine was performed by the oxidation of enzymatically generated H2O2 at + 0.7 V vs. Ag/AgCl. The linear working range of the electrode was 2.0 × 10−5 − 3.2 × 10−4 M and the response time was about 50 s. The effects of pH, temperature, enzyme ratio and buffer concentration were investigated and optimum parameters were found to be 7.5, 37°C, 2.5:1 (CI:SO) and 0.05 M, respectively. The stability and reproducibility of the enzyme electrode have been also studied.

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.

Amperometric carbon paste enzyme electrodes with Fe(3)O(4) nanoparticles and 1,4-benzoquinone for glucose determination.

Abstract Two new amperometric carbon paste enzyme electrodes including Fe3O4 nanoparticles with and without 1,4-benzoquinone were developed for glucose determination. Electron transfer properties of unmodified and Fe3O4 nanoparticles and/or 1,4-benzoquinone modified carbon paste electrodes were investigated in 0.1 M KCl support electrolyte containing Fe(CN)63−/4− as redox probe by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. Fe3O4 nanoparticles increased electron transfer at solution/electrode interface. The parameters affecting the analytical performance of the enzyme electrode have been investigated in detail and optimized for Fe3O4 nanoparticle modified enzyme electrode (Fe3O4–CPEE). Fe3O4 nanoparticles and 1,4-benzoquinone modified enzyme electrode (BQ‐Fe3O4‐CPEE) exhibited linear response from 1.9 × 10‐7 M to 3.7 × 10‐6 M, from 7.2 × 10‐6 M to 1.5 × 10‐4 M and from 1.3 × 10‐3 M to 1.2 × 10‐2 M with an excellent detection limit of 1.9 × 10‐8 M. BQ‐Fe3O4‐CPEE was used for determination of glucose in serum samples and results were in good agreement with those obtained by spectrophotometric method.

Determination of Creatine in Commercial Creatine Powder with New Potentiometric and Amperometric Biosensors

New potentiometric and amperometric biosensors were developed for the determination of creatine. The potentiometric creatine biosensor was prepared by immobilizing urease and creatinase on poly(vinylchloride) (PVC) ammonium membrane electrode containing palmitic acid prepared by using nonactine as an ammonium-ionophore. The linear working range of the biosensor was 1.0 × 10−5–1.0 × 10−3 M and the response time was about 60 s. The optimum pH, temperature, and buffer concentration were found to be 7.0, 20°C, and 5 mM, respectively. The slope of the electrode was 49.2 mV/p[creatine]. The storage stabilization of the biosensor was investigated and 40–45% decrease in the response was detected after 2 months. The amperometric creatine biosensor was prepared by immobilizing creatinase (CI) and sarcosine oxidase (SO) in a poly(vinylferrocenium) matrix onto the surface of a platinum working electrode by crosslinking with glutaraldehyde (GA) and bovine serum albumine (BSA). Determination of creatine was performed by the oxidation of enzymatically generated H2O2 at +0.7 V vs. Ag/AgCl. The linear working range of the biosensor was 2.0 × 10−5–3.2 × 10−4 M and the response time was about 50 s. The effects of pH, temperature, enzyme ratio and buffer concentration were investigated and optimum parameters were found to be 7.5, 37°C, 2.5:1 (CI:SO) and 0.05 M, respectively. The determination of creatine in commercial creatine powder was successfully carried out with these creatine biosensors by using the standard addition and calibration curve methods. The results were in good agreement with those obtained from Jaffé method at 95% confidence level.

Graphene and tricobalt tetraoxide nanoparticles based biosensor for electrochemical glutamate sensing.

Abstract An amperometric biosensor based on tricobalt tetraoxide nanoparticles (Co3O4), graphene (GR), and chitosan (CS) nanocomposite modified glassy carbon electrode (GCE) for sensitive determination of glutamate was fabricated. Scanning electron microscopy was implemented to characterize morphology of the nanocomposite. The biosensor showed optimum response within 25 s at pH 7.5 and 37 °C, at +0.70 V. The linear working range of biosensor for glutamate was from 4.0 × 10−6 to 6.0 × 10−4 M with a detection limit of 2.0 × 10−6 M and sensitivity of 0.73 μA/mM or 7.37 μA/mMcm2. The relatively low Michaelis–Menten constant (1.09 mM) suggested enhanced enzyme affinity to glutamate. The glutamate biosensor lost 45% of its initial activity after three weeks.

An Fe3O4-nanoparticles-based amperometric biosensor for creatine determination

Abstract An amperometric biosensor for the detection of creatine was designed, based on carbon paste electrode modified with Fe3O4 nanoparticles. Electron transfer properties of unmodified and Fe3O4-nanoparticles-modified carbon paste electrodes were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. Fe3O4 nanoparticles increased the surface area and electric conductivity of the electrode, thus enhancing the sensitivity of the electrode. Optimum pH, buffer concentration, working potential and enzyme loading were selected as 7.0; 0.05 mol L−1; +0.30 V and 2.0 Unit creatinase (CI), 1.0 Unit sarcosine oxidase (SO), respectively. The purposed biosensor exhibited linear response from 2.0 × 10−7 mol L−1 to 3.8 × 10−6 mol L− 1 and from 9.0 × 10− 6 mol L−1 to 1.2 × 10− 4 mol L− 1 with a detection limit of 2.0 × 10−7 mol L−1. Biosensor was used for determination of creatine in commercial creatine powder samples and showed a good sensing performance.

Electroanalytical Characterization of Montelukast Sodium and Its Voltammetric Determination in Pharmaceutical Dosage Form and Biological Fluids

The electrochemical properties of montelukast sodium (MKST) at zinc oxide nanoparticles modified carbon paste electrode were investigated by cyclic voltammetry and square wave voltammetry. All studies were based on the irreversible and adsorption-controlled electrochemical reduction signal of montelukast sodium at about -0.7 vs. Ag/AgCl at pH 2.3 in methanol-Britton-Robinson buffer mixture. This adsorptive character of the molecule was used to develop a novel, validated, rapid, selective and simple square wave cathodic adsorptive stripping voltammeric method for the direct determination of montelukast sodium in pharmaceutical and biological fluids without time-consuming steps prior to drug assay. Peak current of electrochemical reduction of montelukast sodium was found to vary linearly with the concentration in the range from 1.0 × 10-8 to 1.28 × 10-6 mol L-1. In this method, limit of detection was found to be 7.7 × 10-9 mol L-1. The method was applied to determine the content of MKST tablet and spiked human serum.