Dynamic Electrochemistry: Methodology and Application

Mechanism of charge transport by redox metal complexes confined in polymer matrices

The mechanism of charge transport by metal complexes confined in polymer matrices is reviewed. There are two possibilities, one where the charge propagates in the matrix by diffusion of redox center molecules, and the other where the charge propagates by hopping between redox center molecules. The mechanism can be decided by investigating the dependence of the charge propagation rate on the redox center concentration, since in the diffusion mechanism the rate is first-order with respect to the concentration, while in the hopping mechanism it is second-order. In the hopping mechanism the charge-hopping distance can be analyzed by assuming a random distribution of the redox center in the matrix. The mechanism of charge transport by typical redox centers such as metal porphyrins, metal phthalocyanines, [Formula: see text] and methylviologen confined in a polymer membrane is presented and the charge-hopping distance is determined.

Ultramicroelectrode Voltammetric Investigation of the Micellar Phase of Sodium Dodecyl Sulfate in Aqueous Solution

Ultramicroelectrode voltammetric measurements have been made on Sodium Dodecyl Sulfate (SDS) in aqueous solutions using K4Fe(CN)6 as the electroactive probe and H2SO4 as the supporting electrolyte. By extrapolation, the SDS micellar diffusion coefficient (D m), hydrodynamic radius (R m), aggregation number (n), and the molecular weight of SDS micellar in aqueous solutions at various surfactant concentrations are obtained. The partition coefficients, KD , of the electroactive probe between micelle and water continuous phase are also estimated. The results suggest that the probe is sensitive to the surfactant concentration and reflect the changes of the structure and the hydrophobic nature of micelles.

Electrochemical detector based on sol-gel-derived carbon composite material for capillary electrophoresis microchips

An on-chip disk electrode based on sol-gel-derived carbon composite material could be easily and reproducibly fabricated. Unlike other carbon-based electrodes reported previously, this detector is rigid, convenient to fabricate, and amenable to chemical modifications. Based on the stable and reproducible characters of this detector, a copper particle-modified detector was developed for the detection of carbohydrates which extends the application of the carbon-based electrode. In our experiments, the performance of the new integrated detector for rapid on-chip measurement of epinephrine and glucose was illustrated. Experimental procedures including the fabrication of this detector, the configuration of separation channel outlet and electrode verge, and the performance characteristics of this new electrochemical detector were investigated.

The analysis of uric acid in urine using microchip capillary electrophoresis with electrochemical detection

Clinical studies have linked irregular concentrations of uric acid in urine to several diseases. Conventional methods for the measurement of uric acid are however temperature-dependent, expensive, and require labile reagents. The miniaturization of analytical techniques, specifically capillary electrophoresis, offers an ideal alternative for clinical analyses such as uric acid determination. The added benefits include reduced reagent and analyte consumption, decreased maintenance costs, and increased throughput and portability. A microchip capillary electrophoresis-electrochemical system for the analysis of uric acid in urine is described. The poly(dimethylsiloxane) (PDMS)/glass microchip utilizes amperometric detection via an off-chip platinum working electrode. Linear responses from 1 to 165 microM and 15 to 110 microM were found for dopamine and uric acid, respectively. The limit of detection for both compounds was 1 microM. Once characterized, the system was used to measure the concentration of uric acid in a dilute urine sample in less than 30 s. The measured uric acid concentration was verified with the uricase reaction and found to be acceptable. Six additional urine samples were evaluated with the microchip device and the uric acid concentration for each sample was found to be in the expected clinical concentration range.

Stripping analysis of nucleic acids at a heated carbon paste electrode

A new electrically heated carbon paste electrode has been developed for performing adsorptive stripping measurements of trace nucleic acids. Such coupling of electrochemistry at electrically heated electrodes with adsorptive constant-current stripping chronopotentiometry offers distinct advantages for trace measurements of nucleic acids. The application of increased temperatures during the deposition step results in dramatic (4-34-fold, depending on temperature applied) enhancement of the stripping signal. Such improvement is attributed to the accumulation step at the heated electrode. Forced thermal convection near the electrode surface facilitates the use of quiescent solutions and hence of ultrasmall volumes. Using an electrode temperature of 32 degrees C and a quiescent solution during the 1-min accumulation, the response is linear over the 1-8 mg/L range tested, with a detection limit of 0.5 mg/L. Such electrode heating technology offers great promise for various applications involving thermal manipulations of nucleic acids.

Thin-film glucose biosensor based on plasma-polymerized film: simple design for mass production

We propose a simple thin-film glucose biosensor based on a plasma-polymerized film. The film is deposited directly onto the substrate under dry conditions. The resulting films are extreme thin, adhere well onto the substrate (electrode), and have a highly cross-linked network structure and functional groups, such as amino groups, which enable a large amount of enzyme to be immobilized. Since this design allows fabrication through a dry process, with the exception of the enzyme immobilization, which is the last stage of the process, the chip fabrication can be designed as a full-wafer process to achieve mass production compatibility. The resulting sensors produced using this film are more reproducible, exhibit lower noise, and reduce the effect of interference to a greater degree than sensors made using conventional immobilization methods, e.g., via 3-(aminopropyl)triethoxysilane. The obtained film is a good interfacial design between enzyme and electrode; enzyme two-dimensionally locates very close to the electrode in a manner that is quite reproducible. Therefore, a wide dynamic range (up to 60 mM) and rapid response time (11.5+/-0.8 s) were obtained. Because of its highly cross-linking network structure, the amperometric response due to interferences such as ascorbic acid and acetaminophen was reduced by size discrimination of plasma-polymerized films.