Alexander M. Yacynych

Electropolymerized films to prevent interferences and electrode fouling in biosensors

Abstract Electrochemical biosensors are constructed by all-chemical means for the determination of serum glucose by flow-injection analysis. The electrode is protected from interferences and fouling by electropolymerized films. The effectiveness of various electropolymerized films are evaluated. An electropolymerized film of 1,3-DAB/resorcinol gave the best protection and stability. The advantage of all-chemical construction is that it can be used for any size or shape sensor. A variety of electrode materials are used. Biosensors are constructed by platinizing the electrode, if it is carbon. Glucose oxidase is immobilized onto the surface by crosslinking with glutaraldehyde, followed by an electropolymerized film. Thermal stability of the enzyme also is investigated. The biosensor, with poly(1,3-DAB/resorcinol), is effective for 5 months with periodic use, has a linear response over the human physiological range (2.5–10 m m ), and standard serum samples are accurately determined within ±3%.

Electropolymerized 1,3-diaminobenzene for the construction of a 1,1′-dimethylferrocene mediated glucose biosensor

Abstract An electron-mediated glucose biosensor was constructed from spectroscopic-grade graphite electrodes in three steps. A non-conducting electropolymerized film serves to screen out electroactive interferents and prevents electrode fouling. The electron mediator 1,1′-dimethylferrocene is adsorbed on, and retained by the polymer film-modified electrode. Glucose oxidase is then crosslinked with glutaraldehyde on the modified electrode. This yields a biosensor with linear glucose response (2–76 mM) at +150 mV vs. SCE, and little or no interference from oxygen, with a lifetime of up to four months.

Galactose biosensors using composite polymers to prevent interferences.

A biosensor using a composite polymer to prevent interferences was used in a flow injection analysis system for the detection of galactose in human plasma. The biosensor consisted of galactose oxidase immobilized on a platinized carbon electrode that had been modified with a composite polymer. The composite polymer showed improved selectivity to hydrogen peroxide compared with either of its individual polymeric components, Nafion and a copolymer of diaminobenzene and resorcinol. The composite polymer minimized the effect of possible interference from urate, ascorbate, and acetaminophen. This analytical system had a minimum detection limit of 50 microM, linearity to 6 mM, a storage stability of greater than 30 days, and a high sample throughput (approx. 120 samples/h).

Electrochromatography—a preliminary study of the effect of applied potential on a carbonaceous chromatographic column

Abstract The preparation of a trimethylchlorosilane-modified carbon support material and the construction of a three-electrode high-performance liquid chromatographic column are described. The effects of applied potential on the capacity factors are described. The capacity factors decrease by factors of 8 for toluene, 2 for phenol, and 1.1 for pyridine as the applied potential is changed from +0.8 to −0.8 V vs. Ag.

Chemically modified reticulated vitreous carbon electrode with immobilized enzyme as a detector in flow-injection determination of glucose

Abstract The construction and response of a chemically modified electrode in which glucose oxidase (E.C. 1.1.3.4) is covalently attached to the surface of reticulated vitreous carbon is reported. Hydrogen peroxide produced by the oxidation of glucose is consumed at the electrode suface, which is held at + 0.9 V vs. a saturated calomel reference electrode. The hydrodynamic and electrochemical properties of the reticulated vitreous carbon electrode substrate make the electrode attractive for use in flow systems. The current varies nonlinearly with glucose concentration throughout most of the range examined (10−1−10−4 M). At concentrations of 2.5–10 mM, response is approximately linear with concentration, with a sensitivity of about 400 nA mM−1. Relative standard deviation for five sample at 10 mM−1 is less than 2%.

Chemically modified graphite electrode with immobilized enzyme as a potentiometric sensor for some l-amino acids

Abstract A chemically modified electrode with immobilized enzyme was constructed by covalent attachment of l -amino acid oxidase (E.C. 1.4.3.2) to a graphite rod via chemical modification of the electrode surface. Logarithmic response with concentration of selected l -amino acids was observed in the 10-2–10-5 M range. The electrodes displayed slopes of 24–29 mV/decade over the tested concentration range for l -phenylalanine, l -methionine, and l -leucine. The electrode slope degraded by 33% after 78 days under the defined storage conditions. Interaction of hydrogen peroxide with surface groups generated during cyanuric chloride modification appears to be the major contributor to the potentiometric response. Cations change the electrode potential but have essentially no effect on the electrode slope. A plausible model describing the mechanism of response is presented.

Reticulated vitreous carbon electrode materials chemically modified with immobilized enzyme

Abstract The direct covalent attachment of glucose oxidase to the surface of reticulated vitreous carbon (RVC), a honeycomb carbonaceous material, is reported. The activity of the bound enzyme on different types of RVC, and the activity of adsorbed blanks are presented.

Potentiometric response of graphite electrodes coated with modified polymer films

Abstract Graphite electrodes coated with chemically-modified polymer films are described. Several different polymers were used, including poly(acrylic acid), poly[triethyl(vinylbenzyl)ammonium chloride], poly[trihexyl(vinylbenzyl)ammonium chloride], and poly[trihexyl(vinylbenzyl)ammonium thiocyanate]. A cation-responsive electrode can be prepared from poly(acrylic acid)-coated graphite. Anion-responsive electrodes can be prepared from graphite coated with polymeric quaternary amines. In these electrodes, the ion-sensing species is irreversibly attached to the polymer (rather than physically entrapped within a polymer matrix); this factor eliminates leaching of the active component, and the addition of a plasticizer is unnecessary. A selective sensor for thiocyanate is described; it yields a Nernstian response over the concentration range 1 × 10−1–1 × 10−5 M sodium thiocyanate.

Direct electron transfer in immobilized flavoenzyme chemically modified graphite electrodes

Abstract Direct electron transfer between covalently immobilized flavoenzymes and a cyanuric chloride-modified graphite electrode is observed via differential pulse voltammetry. L-Amino acid oxidase and xanthine oxidase display peaks arising from the reduction of flavin adenine dinucleotide. Peak current enhancements are observed for both covalently attached enzymes compared to their free and adsorbed state voltammograms. Studies concerning flavin removal and reconstitution indicate that xanthine oxidase contains multiple flavin chromophores which are nonequivalent.

Thermal studies of carbonaceous electrode materials chemically modified with cyanuric chloride

Abstract A thermoanalytical investigation of chemically modified graphite and activated carbon is presented. Evaluation of thermal curves shows that radio-frequency oxygen plasma treatment is superior to electrochemical oxidation for increasing surface functional group concentrations, which when chemically reduced, can be used for cyanuric chloride binding. The amount of cyanuric chloride bound to the carbonaceous surface is determined by both potentiometric titration of hydrolyzed chloride and magnitude of weight loss at 275–290°C. The species evolved in this temperature range is identified by temperature-programmed mass spectrometry as cyanuric acid.