Biomedical subjects

Cynthia G Zoski

Publications and source records attributed to Cynthia G Zoski.

5 recordsLinked to original sources

PubMed2006

Polymer films on electrodes: investigation of ion transport at poly(3,4-ethylenedioxythiophene) films by scanning electrochemical microscopy.

Electropolymerization, morphology characterization, and ion transport of poly(3,4-ethylenedioxythiophene) (PEDOT) films doped with different counterions (chloride, ferrocyanide (FCN), and poly(p-styrenesulfonate) (PSS-)) on a platinum electrode were investigated using scanning electrochemical microscopy (SECM) during both potential step (chronocoulometric) and cyclic voltammetric scans. An ultramicroelectrode (UME) tip was positioned close to the surface of a PEDOT-modified substrate electrode, and the responses of both electrodes to a substrate potential step or linear sweep were monitored simultaneously. Chloride or ferrocyanide (FCN) ejection during PEDOT reduction was shown to be a function of the reduction potential. The nature of the cation in the bulk solution was not found to be important in the kinetics of ion transport in PEDOT+/FCN- films. Direct evidence for the incorporation of cations of Ru(NH3)6(3+/2+) in a PEDOT film during its reduction was also obtained by SECM measurements. The adsorption of Ru(NH3)6(3+) in fully oxidized PEDOT+/PSS- films was observed and attributed to ion exchange between the Na+ co-ion of PSS- and Ru(NH3)6(3+) in the bulk solution.

Bridged Bicyclo Compounds, Heterocyclic↗

PubMed2005

Fabrication of 3D gold nanoelectrode ensembles by chemical etching.

A simple chemical etching procedure based on the solubility of polycarbonate membranes in solvent mixtures is reported for fabricating 3D gold nanoelectrode ensembles. A solvent ratio of 50:50 dichloromethane/ethanol was found to be optimum for selective controlled etching of the surface layers of the polycarbonate membranes to expose up to 200-nm lengths of gold nanowires. The absence of double layer charging current in cyclic voltammograms of the resulting 3D nanoelectrode ensemble verified that the seal between the gold nanowires and the polycarbonate membrane was not compromised as a result of the chemical etching.

Gold↗

PubMed2004

Scanning electrochemical microscopy: theory and characterization of electrodes of finite conical geometry.

Finite conical electrodes, which are of particular interest as probes for imaging of surfaces using scanning electrochemical microscopy (SECM), in kinetic studies and in probing thin films were investigated. Theoretical SECM tip current-distance feedback (approach) curves for a finite conical electrode were calculated by numerical (finite element) analysis and compared to an earlier approximate model. The SECM curves obtained depended on the ratio of the base radius of the cone to the height of the cone and on the thickness of the insulating sheath. A new approach to fabricating conical tips of Pt in glass is described. These were used to obtain approach curves over both electrically conducting and insulating substrates. Comparison of experimental and simulated SECM approach curves provided a sensitive method of evaluating the size and shape of finite conical electrodes.

Electrochemistry↗

PubMed2003

Scanning electrochemical microscopy. 46. Shielding effects on reversible and quasireversible reactions.

An approximate theory for the feedback mode of the scanning electrochemical microscope (SECM) is developed to interpret the effects of substrate shielding on an ultramicroelectrode tip during a recording of iT versus d curves (approach curves) for reversible and quasireversible kinetics at a substrate surface. The resulting expressions for the tip current, iT, show a good fit to more accurate SECM simulations as well as to the experimental response of a reversible and quasireversible reaction. SECM shielding experiments thus give an interesting new insight into SECM approach curves over electrodes at different potentials, which suggest possible applications to measuring heterogeneous kinetics for fast reactions and diffusion coefficient determination.

Journal Article↗

PubMed2002

Steady-state limiting currents at finite conical microelectrodes.

The investigation of steady-state diffusion-limiting currents at finite conical microelectrodes is reported. Such electrodes are of particular interest as probes in studies of kinetic reactions, measurements in microenvironments, and high-resolution electrochemical imaging. The diffusion-limiting currents were calculated using numerical (finite element) analysis and compared to those obtained at inlaid disk and hemispheroidal microelectrodes. Time-dependent simulations demonstrating the approach of the diffusion current to a steady-state value are also reported. The steady-state diffusion-limiting currents obtained were found to be a strong function of the electrode geometry, including the aspect ratio of the cone and the thickness of the insulating sheath. Thus, simple, approximate analytical expressions which account for these geometrical dependencies in the simulated steady-state diffusion-limited currents are also reported. As a limiting case, an analytical approximation was obtained for the steady-state current to a microdisk as a function of the insulator thickness. The use of these approximate equations in calculating electrode radii from steady-state diffusion-limiting currents is demonstrated, and good agreement was found with previously reported experimental studies. Use of the frequently implemented hemispherical theory to analyze steady-state diffusion-limiting currents obtained with finite conical microelectrodes is shown to result in an experimentally acceptable underestimation of the electrode radius.

Journal Article↗