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Biomedical subjects

W Gorski

Publications and source records attributed to W Gorski.

7 recordsLinked to original sources
PubMed2001

Bioinorganic composites for enzyme electrodes.

Sparingly soluble redox salts were combined with a model enzyme, glucose oxidase, in a host matrix of a biopolymer chitosan to form bioinorganic composite films on the surface of glassy carbon electrodes. Four redox salts, each containing the Ru(NH3)6(3+) cation and a selected anion, such as Ru(CN)6(4-), Fe(CN)6(4-), Co(CN)6(3-) or IrCl6(3-), were studied. The composition and catalytic properties of such composite materials toward glucose oxidation were investigated by spectroscopic and electrochemical methods. The composite films provided an oxygen-independent electrical communication between the enzyme's redox centers and a glassy carbon surface at a potential as low as -0.10 V vs Ag/AgCl(3 M Cl-). The nature of the electrical communication is discussed in terms of redox mediation by the Ru(NH3)6(3+)-containing ion pairs formed inside the biocomposites. The kinetic significance of the mediator's charge is considered by postulating that neutral ion pairs are more efficient redox mediators of the enzymatic reaction than those negatively charged. The low operating potential of enzyme electrodes based on the bioinorganic composites allows for an interference-free determination of glucose. The design of the biocomposites is generic and can incorporate oxidoreductase enzymes other than glucose oxidase to provide a host of biosensors for biologically and environmentally important analytes.

Biosensing Techniques↗
PubMed2000

Iridium-based electrocatalytic systems for the determination of insulin.

Two electrochemical catalytic systems for the determination of insulin were developed. The homogeneous system was based on the oxidation of insulin by chloro complexes of iridium(IV). Kinetic studies revealed that the aquation of iridium complexes activated them toward the oxidation of insulin in acidic solutions; e.g., the rate constant was equal to 25, 900, and 8,400 L mol(-1) s(-1) for the oxidation of insulin by the IrCl62-, Ir(H2O)CI5-, and Ir(H2O)2Cl4 complexes, respectively. The inertness of the iridium complexes argued for the outer-sphere mechanism of the homogeneous oxidation reaction. Electroplating of aquated iridium complexes on the glassy carbon electrode resulted in the formation of the iridium oxide (IrOx) surface film, which was used in the heterogeneous detection system for insulin. The catalytic activity of the IrOx film toward insulin oxidation was ascribed to a combination of electron-transfer mediation and oxygen transfer which was related to the acid/base chemistry of the film. The IrOx film electrode was used as an amperometric detector for flow injection analysis of insulin in pH 7.40 phosphate buffer. Linear least-squares calibration curves over the range 0.05-0.50 microM (five points) had slopes of 35.2 +/- 0.4 nA microM(-1) and correlation coefficients of 0.999. The detection limit for insulin was 20 nM using the criterion of a signal of 3 times the peak-to-peak noise. The advantageous properties of the detector based on the IrOx film are its inherent stability at physiological pH, high catalytic activity toward insulin oxidation, and simplicity of preparation.

Algorithms↗
PubMed2000

Electrode coatings based on chitosan scaffolds.

Thin films of a biopolymer chitosan (CHIT) were cast on glassy carbon electrodes, modified by grafting Lucifer Yellow VS dye (LYVS) onto chitosan chains, and cross-linked with glutaric dialdehyde (GDI). The ion-transport and ion-exchange properties of such polymeric structures (CHIT, CHIT-LYVS, CHIT-LYVS-GDI) were studied using cyclic voltammetry, rotating disk electrode, and flow injection analysis. The results showed that the chitosan matrix supported a fast ion transport as demonstrated by aqueous-like values of the apparent diffusion coefficients of Ru(NH3)6(3)+ and dopamine in the films. Anionic LYVS dye introduced a permselectivity against anions (e.g., Fe(CN)6(4)-, ascorbate) into the CHIT-LYVS films. The cross-linking of such films with GDI further increased their permselectivity as well as their stability. A unique combination of high permselectivity and fast ion transport in the CHIT-LYVS-GDI films is discussed in terms of the mixed-transport mechanism involving both pore and membrane diffusion in a highly hydrated chitosan matrix. The results indicate that the chemically modified chitosan is an attractive new coating for the development of fast, selective, and reversible sensors.

Carbohydrate Sequence↗
PubMed1999

Oxygen microsensor and its application to single cells and mouse pancreatic islets.

An oxygen microsensor with a < 3-micron tip diameter was developed for monitoring oxygen levels at single cells and mouse pancreatic islets. The sensor was fabricated by electrochemically recessing an etched Pt wire inside a pulled glass micropipet and then coating with cellulose acetate. This fabrication process was found to be simpler than previous oxygen electrode designs of comparable size. The microsensors had a average sensitivity of 0.59 +/- 0.29 pA/mmHg (mean +/- SD, n = 42), signals that were minimally perturbed by convection, and response times of < 1 s. The electrode was used to measure the oxygen gradient around and inside single mouse islets. The measurements demonstrate that oxygen levels within even the largest islets at maximal glucose stimulation are 67 +/- 1.6 mmHg (mean +/- SD, n = 5), indicating that islets have adequate oxygen supplies by diffusion under tissue culture conditions to support insulin secretion. The electrode was also used to record the dynamics of oxygen level at single islets as a function of glucose concentration. As glucose level was changed from 3 to 10 mM, oxygen level decreased by 15.8 +/- 2.3 mmHg (mean +/- SEM, n = 6) and oscillations with a period of 3.3 +/- 0.6 min (mean +/- SEM, n = 6) appeared in the oxygen level. In islets bathed in quiescent solutions containing 10 mM glucose, similar oscillations could be observed. In addition, in the quiet solutions it was possible to detect faster oscillations with a period of 12.1 +/- 1.7 s (mean +/- SEM, n = 6) superimposed on the slower oscillations. Oxygen consumption could also be observed at single insulinoma cells using the electrode. Individual cells also showed oscillations in oxygen consumption with a period of a few seconds. The results demonstrate that the electrode can be used for dynamic oxygen level recordings in biological microenvironments.

Animals↗