Biomedical subjects

Barna Kovács

Publications and source records attributed to Barna Kovács.

3 recordsLinked to original sources

PubMed2003

Optical biosensor for urea with improved response time.

An optical biosensor for urea measurements was developed. The operation of the sensor is based on the well-known urease enzyme-catalyzed hydrolysis of urea. The ammonium ions liberated in the reaction are detected with an ion selective optode membrane containing nonactin as ion selective ionophore and ETH 5294 chromoionophore in a thin (1 microm) plasticized poly(vinylchloride) film. The basic sensing element was home made of a microscope glass slide, a HeNe laser light source, photodiode light detector and light in coupling, de-coupling elements. The transducer membrane and the enzyme containing reaction layer were sandwich-cast with spin coating onto the surface of the sensing slide. The attenuation of the laser light propagating inside the glass wave-guide was used as signal for urea measurements. With this arrangement membranes provided good sensitivity (0.05 absorption unit when going from 0.1 to 1 mM urea) and short (16-20 s) response time. Taking advantage on the improved response time, flow injection urea measurements were made in the 0.01-2 mM concentration range. Thirty sample/hour analysis-rate, good peak-to-peak reproducibility (RSD=0.02) and recovery (95-104%) was achieved with buffer diluted urea solutions. Applications for the analysis of real samples are planned to do in the future.

Biosensing Techniques↗

PubMed2003

Investigation of concentration profiles inside operating biocatalytic sensors with scanning electrochemical microscopy (SECM).

Scanning electrochemical microscopy (SECM) with amperometric or potentiometric measuring tips was used to investigate biocatalytic reactions inside the enzyme layer of a biosensor during its operation. The well known glucose oxidase catalyzed oxidation of glucose has been selected for the studies. Local, instantaneous concentration of dissolved oxygen and hydrogen peroxide was studied observing the amperometric current while miniaturized potentiometric tip served for local pH measurements. Liquid enzyme layer immobilized with Cellophane membrane or cross linked polyacrilamide gel membrane containing entrapped enzyme served for biocatalytic media in the SECM imaging. Local maximum of H(2)O(2) and minimum of O(2) profiles were found at approximately 200 microm far from the substrate/enzyme layer boundary. From the experimental findings guidelines to design well functioning biocatalytic sensors could be concluded. The concentration profiles obtained with SECM techniques were compared with the results of simple model calculations carried out with the method of finite changes. Most of earlier made SECM studies dealing with enzyme reactions imaged the electrolyte being in contact with the immobilized enzyme. The data in our investigation, however, were collected inside the working catalytic layer.

Biosensing Techniques↗

PubMedDate not supplied

Opto-electrochemical planar wave-guide sensor for copper (II) ion.

An opto-electrochemical sensor for copper (II) ion was developed. The sensor consists of a planar conductive indium-tin-oxide (ITO) glass support, which was coated by a polymeric copper (II) sensitive membrane. The sensing membrane is made of plasticized polyurethane matrix containing Zincon colorimetric reagent immobilized as ion pair with tetraoctylammonium ion. The instrumentation used commonly for wave-guide sensor development was extended with a potentiostat that made possible the control of the electric potential of the conductive surface. In this way the transport rate of ionic species through the membrane-sample interface could be influenced. In the presence of copper (II) ions the color of the membrane turned from red to blue, which was monitored optically. By applying positive potential to the conductive surface the direction of the ion diffusion at the membrane/sample interface was changed. As a result the sensing layer was regenerated within 2 minutes and was ready for further measurement. The sensor measured Cu(2+) ion in a concentration range of 1-200 microM.

Azo Compounds↗