Selma Mutlu

Glow-discharge-treated cellulose acetate (CA) membrane for a high linearity single-layer glucose electrode in the food industry

Abstract The aim of this study was to develop a single-layer glucose enzyme electrode with extended linearity to be used in the food industry in order to determine the glucose content. An amperometric-based probe-type glucose enzyme electrode with Pt working electrode and Ag/AgCl reference electrode polarised at +650 mV was used. In this study, permselective behaviour of different polymeric membranes, which were prepared in our laboratory (cellulose acetate, polyurethane, polyetersulphone) and commercially available tract-etched polycarbonate, were investigated at different pH values (pH 4, 6, 7.4, 10) to estimate the magnitude of interferences caused by a group of different electroactive compounds. The selectivity tests showed that cellulose acetate membranes were the most convenient structure to establish a single-membrane recognition layer. The single surface of the cellulose acetate membranes was then modified with a plasma polymerisation technique at different glow-discharge parameters with amylamine monomer in order to show the effect of plasma polymerisation. The plasma-treated surface of the membranes was activated with glutaraldehyde then glucose oxidase (GOD) immobilised onto this site. The linearity and response time of these electrodes were investigated at pH 4 and 6. According to the results of linearity and response time tests, cellulose acetate membranes treated with amylamine at 5 W/20 min showed the best result. The linearity and response time of this electrode were found to be 320 mM glucose and 500 s, repectively at pH 4. Finally, the GOD electrode which was prepared with the most convenient membrane was used to determine the glucose content of some food stuff. Similar results were observed with the conventional measurement method.

Glow-discharge treated piezoelectric quartz crystals as immunosensors for HSA detection

The aim of this study is to develop an immunoaffinity sensor based on piezoelectric crystals for human serum albumin (HSA) detection in aqueous media. Quartz crystals were treated with ethylene diamine (EDA) plasma in a glow-discharge apparatus in order to substitute amino groups on their surfaces. Then anti-HSA antibodies were immobilized via these amino groups by using glutaraldehyde (GA) as cross-linker. Immobilization of the antibody on the quartz crystal was examined for different pH, antibody concentration and treatment time. The optimum conditions for anti-HSA immobilization were evaluated by the measurements of the activity of the surface against HSA. The optimum values of pH, antibody concentration and treatment time were found 6.2, 0.15 mg/ml and 2 h, respectively. For detection of HSA into the solution, two methods were used. In the first (dip and dry) method, the frequency shifts were measured in air after the 1 h interaction of the anti-HSA immobilized crystals with HSA solution. In the other (direct) method, the frequency shifts were followed continuously for 60 min. while the probe was immersed in the HSA solution. An increase for the frequency shifts was observed with increasing of HSA concentration of 16-128 microg/ml. Both the immobilization and antibody-interaction conditions were found important on the extend of these specific interaction. The relations between the HSA concentrations and frequency shifts were exponential in both methods.

Hemodynamic monitoring of the contralateral testis during unilateral testicular torsion describes the mechanism of damage

Contralateral testicular perfusion during unilateral testicular torsion was evaluated using simultaneous blood flow and O2 content determinations. Two groups, each consisting of 7 rats, were studied. Sham operation or 720° clockwise twisting was performed on the left testes, and blood flow, O2 content and temperatures were monitored in the right testes for 180 min. An ultrasonic perivascular Doppler flowmeter system, an electronic thermometer and an O2 electrode were used for the monitoring. The contralateral testicular blood flow and relative O2 contents were stable in the control group. However, the initial and 180 min blood flow values decreased from 0.21 ± 0.04 to 0.11 ± 0.02 ml/min (p < 0.001), and the O2 contents from 0.857 ± 0.123 to 0.319 ± 0.037 (1.0 corresponds to 19.6 mm Hg pO2, p < 0.05) in the experimental group. Unilateral testicular torsion decreases the blood flow and O2 content of the contralateral testis. The contralateral testicular injury encountered following unilateral testicular torsion might result from hypoxia following the decrease in blood flow.

An Immunosensor: Immobilization of Anti-HBs Antibody on Glow-Discharge Treated Piezoelectric Quartz Crystal for HBs-Ag Detection

ABSTRACT In this study, an immunosensor with a piezoelectric quartz crystal was developed. An oscillator system, in order to measure the frequency shifts caused by the increase of mass on the piezoelectric crystal, was used. The surfaces of the quartz crystals were treated by a glow-discharge technique utilizing ethylene diamine monomer to substitute amino groups on the surface of the crystal. These groups were activated by a bifunctional cross-linker, glutaraldehyde, to immobilize an antibody (so called anti-HBs). Optimum conditions for each of the modification steps for application on the quartz crystal surfaces were established and the results were represented for optimum time, pH and concentration. The sensor was calibrated at optimum conditions for HBs-Ag detection.

Matrix surface modification by plasma polymerization for enzyme immobilization

Polycarbonate (PC) membranes have been treated with dimethylamine (DMA), n-pentylamine (PA) or n-heptylamine (HA) in a glow-discharge apparatus. Amino group concentrations on plasma-polymerized PC membranes were then assayed by binding radiolabelled [1-14C]acetic anhydride to the membrane, followed by scintillation counting. For the different plasma-polymerized membranes different degrees of radiolabelled (125I) glucose oxidase or rennet binding were observed and this was found to be directly related to the surface amino-group concentrations for the appropriate membrane.

The effect of crosslink density on permeability in biosensors: An unsteady-state approach

The influence of cross-linker density (2%, 5% and 10% of glutaraldehyde) on the permeability, P, of the enzyme layer (267.7, 203.5 and 146.0 μm/s respectively for 125I-cortisol-histamine conjugate, CHC (MW: 651) as tracer) in Clark enzyme electrode is reported. A diffusion chamber technique based on unsteady-state analysis for the estimation of permeabilities of radiolabelled molecules through enzyme layer is performed.

A kinetic approach to oxidase based enzyme electrodes: the effect of enzyme layer formation on the response time

Abstract The formation of the enzyme layer of the sandwich type electrodes has been altered and evaluated in terms of kinetic performance. The detection of H 2 O 2 serves to measure the extent of the reaction. The kinetics of the recognition layer are discussed in terms of the response time of the electrode. The enzyme loading between two membranes has altered mass transfer limitations resulting in significant changes in the response of the electrode. The effectiveness factor is used to describe the mass transfer limitations in the system. The response time of the electrode has been increased while the effectiveness factor has been decreased. Steady-state response of the electrodes has been achieved in 43.68 and 98 s for the electrodes including 23.1%, 13.0% and 7.0% (w/w) GOD in a BSA + GOD mixture, respectively. The effectiveness factors for these electrodes have been established at the values of 0.59, 0.38 and 0.16, respectively.

Amperometric determination of enzymatic activity by multienzyme biosensors

A Clark type, amperometric, multienzyme electrode, employing glucose oxidase and mutarotase, was used to determine the enzymatic activity of a model enzyme, invertase, in soluble and immobilized forms. A calibration curve with linear range up to 70 IU of invertase activity corresponding to the 6.0 nA/s of electrode response was sketched. It is shown that, multienzyme electrodes can be utilized as a very rapid, reliable and sensitive tool for the determination of enzymatic activity either in a free or immobilized form.