P.D. Hale

A glucose electrode based on carbon paste chemically modified with a ferrocene-containing siloxane polymer and glucose oxidase, coated with a poly(ester-sulfonic acid) cation-exchanger

Abstract A carbon-paste chemically modified with glucose oxidase and a ferrocene-containing siloxane polymer was further modified by coating the electrode surface with a poly(ester-sulfonic acid) cation-exchanger, Eastman AQ-29D. The polymer is obtained as a homogeneous aqueous dispersion at pH 5–6; when dried, the polymer coating is not water-soluble. The coating was shown not to be detrimental to the enzyme activity but to prevent electrochemically active anionic interferents such as ascorbate and urate from reaching the electrode surface. The polymer coating also prevented glucose oxidase from leaking out of the carbon paste into the contacting solution and protected the electrode surface from fouling agents present in urine and bovine serum albumin. Uncoated electrodes lost some 10-2-15% of their original response to glucose after storage in buffer for three weeks whereas the response of the coated electrodes remained constant. Calibration curves for glucose were strictly linear up to about 5 mM for uncoated and up to 20 mM for coated electrodes. The response current to glucose was not decreased after coating.

Cyclic voltammetry at TCNQ and TTF-TCNQ modified platinum electrodes: A study of the glucose oxidase/glucose and galactose oxidase/galactose systems

Abstract Recent work has shown that the synthetic metal TTF-TCNQ can be used as an electrode material for the oxidation of enzymes containing the prosthetic group flavin adenine dinucleotide (FAD). This direct electron transfer (direct in the sence that oxygen is not a mediator) between reduced enzyme and electrode, a process which does not occur to any measurable extent at a typical metal electrode, is not very well understood. In the present work, electron transfer between reduced glucose oxidase and TTF-TCNQ is investigated using cyclic voltammetry, and it is also shown that TCNQ itself can mediate this electron transfer between the enzyme and a platinum electrode. In addition to the glucose oxidase studies, cyclic voltammetric experiments have been performed on the galactose oxidase system, which contains a copper redox center rather than FAD. The results of these experiments demonstrate that the catalytic ability of TTF-TCNQ in enzyme-based electrochemical sensors is quite general.

Highly ordered thin films of polyheterocycles: A synchrotron radiation study of polypyrrole and polythiophene Langmuir-Blodgett films

Abstract Langmuir-Blodgett films have been made with 3-n-hexadecylpyrrole and 3-n-octadecylpyrrole monomers and copolymers with unsubstituted pyrrole made by chemical polymerization at the air-water interface on a subphase containing FeCl 3 . Langmuir-Blodgett films consisting of mixtures of stearic acid and alkylsubstituted polythiophenes have also been made as bilayer films. The orientation of single and multilayer films on platinum substrates have been studied by Near Edge X-ray Absorption Fine Structure Spectroscopy which also gives information about charge transfer interactions between the aromatic groups and the metallic substrates. The alkylsubstituted pyrroles form highly ordered two-dimensional structures. FeCl 3 initiated copolymerization with unsubstituted pyrrole leads to a more disordered system. In the case of polythiophene-stearic acid bilayers, the stearic acid layers are highly ordered. The poly(alkyl thiophene) layers sandwiched between stearic acid layers, on the other hand, exhibit random orientation of the thiophene moieties.

A FTIR and NEXAFS study of polypyrrole Langmuir-Blodgett films

Abstract 3-n-hexadecylpyrrole and 3-n-octadecylpyrrole have been synthesized, and Langmuir Blodgett films of these compounds have been studied by means of NEXAFS and FTIR spectroscopy. By comparing the spectra of two different polarizations, it was found that the hydrocarbon chains are normal to the substrate surface for LB films with multi-layers. For the monolayer LB films, the hydrocarbon tails are tilted towards the substrate surface due to the interaction between the pyrrole ring and the platinum substrate.

Ferrocene-Modified Siloxane Polymers as Electron Relay Systems in Amperometric Glucose Sensors

Abstract This paper describes the design and testing of amperometric glucose sensors in which electrical communication between the flavin redox centers of glucose oxidase and an electrode is achieved via a network of donor-acceptor relays chemically bound to a flexible siloxane polymer backbone. Procedures are discussed for the synthesis of a variety of mediator(ferrocene)-containing siloxane copolymers which differ in flexibility and in the spacing between redox moieties, and for the optimization of the interaction between the flavin redox centers of glucose oxidase and the polymer-bound electron transfer relay system through investigation of these new flexible polymers in glucose sensors.

Poly(xylylviologen) electron transfer mediators in amperometric glucose sensors

Abstract Water-soluble poly(o-xylylviologen dibromide) and poly(p-xylylviologen dibromide) are shown to efficiently mediate electron transfer from reduced glucose oxidase to a conventional carbon paste electrode. Because of their low oxidation potentials, glucose sensors based on glucose oxidase and these mediators can be operated in a potential range where oxidation of interfering species such as ascorbic acid and uric acid does not occur. The corresponding monomeric materials, benzylviologen bromide and dibenzylviologen dibromide cannot serve as electron transfer mediators as their formal potentials are more negative than that of the flavin redox centers in glucose oxidase.

Orientational behavior of thin films of poly(3-methylthiophene) on platinum: A FTIR and NEXAFS study

Abstract Near edge x-ray absorption fine structure (NEXAFS) and infrared reflection-absorption spectroscopy (IRRAS) have been used to study the orientational behavior of thin films of poly(3-methylthiophene) electrochemically polymerized on a platinum surface. Clear orientational effects, with the thiophene rings predominantly oriented parallel to the platinum surface, were observed when the thickness of the polymer films were within a few hundred A. It was found that more highly ordered films were produced at lower polymerization potential (1.4V vs SCE) than at higher potential (1.8V vs SCE).

Langmuir-Blodgett films of a pyrrole and ferrocene mixed surfactant system

The Langmuir-Blodgett technique was used to study the molecular organization of a mixed 3-hexadecyl pyrrole (3HDP) and ferrocene-derivatized pyrrole (Fc-Py) surfactant system. It has been determined that stable monolayer films of the mixed system could be formed at the air-water interface. The growth and assembly process led to polypyrrole 2-D lattices with heretofore unsurpassed order. In fact, the process of template polymerization, it appears, leads to a new crystal phase for the polypyrrole component of the thin film structure. Various monolayer and multilayer films were prepared on platinum-coated substrates for surface spectroscopic characterization. Near Edge X-Ray Absorption Fine Structure (NEXAFS) studies revealed that highly ordered multilayer structures are being formed. Electrochemical studies have been initiated to determine the feasibility of these films in molecular electronic device applications.

Flavoenzyme-based biosensors with redox polymer electron relays

A description is given of the design and testing of a class of amperometric bioanalytical sensor in which electrical communication between the flavin redox centers of an oxidase and a conventional electrode is achieved by means of a network of donor-acceptor relays chemically bound to a flexible siloxane polymer. Electrochemical results demonstrating this mediated electrical communication are discussed for several polymer/enzyme systems. The molecular weight range for these redox-containing polymeric materials is approximately 2000-10000. Purification of the polymers was achieved by reprecipitation from chloroform solution by dropwise addition to a large excess amount of acetonitrile at room temperature. This reprecipitation was repeated two to three times to ensure that no low-molecular-weight species (which could act as freely diffusing electron transfer mediators) were present. Redox-polymer/glucose-oxidase/carbon-paste electrodes were tested and found to be sensitive to small changes in glucose concentration over a clinically useful range of concentrations.<<ETX>>