A comprehensive overview is presented on the implication of silica-based organic-inorganic hybrid materials in electrochemical science. It involves composite materials of both class I (weak bonds between the organic and inorganic components) and class II (strong chemical bonds). Starting with a description of the common designs of electrodes modified with these hybrids, the review then reports their applications in the various fields of electrochemistry, illustrating the diversity of the organically modified silicates used for this purpose. The mild chemical conditions allowed by the sol-gel process provide very versatile access to these electrochemical devices. They have found many applications in electroanalysis, including preconcentration associated with voltammetric detection, permselective coatings, electrochemical sensors, electrocatalysis, and detectors for chromatography. They were also applied as redox and conducting polymers, as solid polymer electrolytes for batteries, for the design of spectroelectrochemical and electro-chemiluminescence devices, and in the field of electrochemical biosensors.

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Electrochemical Applications of Silica-Based Organic−Inorganic Hybrid Materials

Electrochemical sensors and biosensors based on redox polymer/carbon nanotube modified electrodes: a review.

Cholesterol oxidase: sources, physical properties and analytical applications.

The electropolymerization of different azines from aqueous solutions was investigated. The structure of monomers was systematically varied changing both the nature of the second heteroatom and the substituents in the aromatic rings. Considering the electropolymerization process and the properties of the resulting polymers one can denote polyazines as a new group of electroactive polymers. The electrochemical and spectroelectrochemical investigation of polyazines was done. A hypothesis on azine polymer structure is presented.

Electropolymerized Azines: A New Group of Electroactive Polymers

This review deals with the use of pyridine-nucleotide dependent dehydrogenase enzymes in amperometric biosensor design. The electrochemistry of the nicotinamide coenzymes, their mechanism and the challenges associated with their direct oxidation on solid electrodes are discussed. In addition, a survey of the different solutions proposed in the literature for addressing these problems and some of their applications are presented.

Amperometric biosensors based on NAD(P)‐dependent dehydrogenase enzymes

The electrochemical behavior of a redox-active ferrocene-modified siloxane polymer (PBF) which is capable of acting as an electron mediator for flavin enzymes was examined. By cyclic voltammetry, it was revealed that the redox activity of PSF film was strongly affected by anionic species in the soaking solution. While a highly stable current response corresponding to the ferrocene/ ferricinium (Fc 0 /Fc + ) redox couple of the film was obsersed in NaClO 4 or NaBF 4 supporting electrolyte solutions, the current response gradually decreased by cycling of the potential in an aqueous solution of NaCl, NaNO 3 sodium p-toluenesulfonate, or phosphate buffer

Investigation of electrochemical behavior and mass-transfer process of ferrocene-siloxane polymer film using quartz crystal electrode method

Poly(thionine)-modified electrodes have been prepared using basal-plane pyrolytic graphite, glassy carbon and In-Sn oxide conducting glass as electrode substrates by an electrooxidative polymerization of thionine in both aqueous and acetonitrile media. It was found that the prepared films, the surface concentration of which can be controlled over the range of ca. 10-10-10-8mol cm-2 by appropriately choosing the electropolymerization conditions (e.g., solvent, concentration of thionine and electrolysis time), are electroactive (the formal potential is ca. 0.0V vs. Ag/AgCl at pH 7.0) and chemically stable. The modified electrodes exhibited excellent electrocatalysis for NADH oxidation in neutral aqueous solutions, with an activation overpotential which is ca. 400mV lower than that of a bare electrode. Further, the modified glassy carbon electrode was found to be promising as an amperometric detector for the flow-injection analysis of NADH, typically with a dynamic range of 5μM-1mM.

Preparation of Poly(thionine)-Modified Electrode and Its Application to an Electrochemical Detector for the Flow-Injection Analysis of NADH.

The electrochemical behavior and the response of the quartz crystal microbalance(QCM) for the Langmuir–Blodgett(LB) viologen film have been examined. LB monolayers employed are prepared by electrostatically fixing the viologen monolayer containing the alkyl chain moiety on the poly(potassium 1-sulfatoethylene). The number of monolayers accumulated on the polycrystalline Au electrode of a piezoelectric quartz crystal was controlled by changing the general vertical dipping times. The QCM frequency response for the first reduction scan of viologen dication (V2+) to monocation radical (V+•) shows extremely large frequency increase, qualitatively indicative of mass loss, viscoelasticity decrease, or mechanical stress decrease during the reduction. A frequency increase during the second reduction scan is also observed, although not as large as for the first scan. The frequencies increase continuously with increasing number of scans and the steady-state responses can only be obtained after many repetitive potent...

“In-situ” Quartz Crystal Microbalance Responses and Electrochemistry Regarding Langmuir–Blodgett Film of Viologen Polyion Complex on the Electrode Surface

A new amperometric sensor for determination of free cholesterol based on a bilayer-film coating has been fabricated and its sensor characteristics have been examined by cyclic voltammetry and under steady-state conditions. The electrode substrate was coated with two kinds of polymeric films in a bilayer state, i.e., first with the redox-active cobalt tetrakis(o-aminophenyl)prophyrin polymer (poly-CoTAPP), and then with the enzyme film consisting of bovine serum albumin and cholesterol oxidase (CHOx). In this sensor system for assay of free cholesterol, oxygen consumption could be monitored by measuring the current for oxygen reduction electrocatalyzed by the inner poly-CoTAPP film according to the following reaction sequence:






where reactions 1, 2, and 3 correspond to the cholesterol–cholesterol oxidase enzymatic-reaction, the electrocatalytic reduction of O2 by the poly-CoTAPP film, and the electrode reaction of Co(III/II)TAPP couple in the poly-CoTAPP film, respectively. The reproducible relationship between concentration of free cholesterol and sensor output was obtained. The sensitivity and the dynamic range were found to depend on the amount of CHOx confined in the enzyme film.

A redox-active polymer film mediated enzyme electrode for amperometric determination of free cholesterol

A solid-state reference electrode has been fabricated. Its design is based on a field effect transistor, the gate of which is coated with two kinds of polymeric films in a Bilayer state: the inner layer is an electroactive electropolymerized poly(p, p′ biphenol) film and the outer one is a polyimide film. The electrode characteristics have been examined. The bilayer film-coated reference field effect transistors (RFETs) thus fabricated wereinsensitive to electrolyte ions (including H+ and OH-) under the condition of a constant concentration (e.g., 0.1M) of an electrolyte; thus they could function as a reference electrode. These RFETs showed insensitivity to O2 and less sensitivity to CO2 (compared with the RFET coated with the polyimide film alone), long-term stability and little drift. The results demonstrate that the bilayer film-coated FETs are promising as a solid-state reference electrode coupled with conventional ion-sensitive field effect transistors in a biological system.

Shin Ikeda

Papers

Investigation of electrochemical behavior and mass-transfer process of ferrocene-siloxane polymer film using quartz crystal electrode method

Preparation of Poly(thionine)-Modified Electrode and Its Application to an Electrochemical Detector for the Flow-Injection Analysis of NADH.

“In-situ” Quartz Crystal Microbalance Responses and Electrochemistry Regarding Langmuir–Blodgett Film of Viologen Polyion Complex on the Electrode Surface

A redox-active polymer film mediated enzyme electrode for amperometric determination of free cholesterol

A solid-state reference electrode based on bilayer coating with poly(p,p'-biphenol) and polyimide films for the gate of field effect transistor