Highly selective amperometric glucose sensors based on rhodium-dispersed carbon paste/glucose oxidase electrodes are described. The dispersed rhodium particles exhibit efficient and preferential electrocatalytic activity toward the liberated peroxide species and allow cathodic detection of the glucose substrate at -0.10 V, with no interference from easily oxidizable constituents. Such operation thus eliminates the need for interferant-eliminating enzyme layers, permselective membrane barriers, or artificial electron mediators, hence greatly simplifying the sensor design and fabrication. The sensor selectivity is illustrated in the presence of physiological levels of ascorbic acid, uric acid, acetaminophen, salicylic acid, tyrosine, urea, galactose, and glutathione. Attractive dynamic properties and high sensitivity are also achieved in the absence of membrane barriers. A stable response is observed over several months.Because of the high demand for blood glucose measurements (particularly for treatment and control of diabetes), significant research and development efforts have been devoted to producing reliable glucose sensors.1-1 2 Particular attention has been given to the development of single-use (disposable) strips for self-testing of blood glucose and to implantable devices for continuous in vivo monitoring of this sugar. Amperometric enzyme electrodes have received considerable attention in connection with these self-testing and in vivo applications.

The permeability characteristics and analytlcal applications of a thin-layer glassy carbon detector coated with cellulose acetate film are descrlbed. Access to the surface can be manipulated via a controlled base-hydrolysis of the fllm. As a result of excluding macromolecules from the surface, the stablilty and selectivity are greatly Improved. The range of applications can be extended vla a careful choice of the hydrolysis period. By adding a new dimension of selectivity based on molecular slre, hlgh spectficlty toward smaller analytes Is demonstrated In both flow Injection and ilquld chromatographic systems. Electrode polsonlng, due to protein adsorption or accumulation of reactlon products, Is mlnlmlred.Complex chromatograms can be greatly slmpllfled without lowering the operating potential. The coated electrode exhlblts extension of the linear range, In situations where a nonllnear response Is obtalned at the bare electrode. Varlous analytes and lnterferents, representing a wide range of molecular slres, are tested. Appllcablllty to urine samples Is demonstrated.

No abstract

The preparation of metal-dispersed carbon paste electrodes, based on mixing an organic binder with metalized graphite, Is described. Such electrodes combine the efficient electrocatalytlc activity of metal microparticles with the attractive properties of carbon paste matrices. The ability to catalyze the slow electrode reactions of hydrogen or organic peroxides, hydrazine compounds, ascorbic acid, and dlhydronlcotlnamlde adenine dHiudeotlde Is Illustrated. Carbon pastes doped with different metals (Pt, Pd, and Ru) exhibit different electrocatalytlc activities, background current contributions, and hence analytical performances. Co immobilization of an oxidase enzyme allows coupling of a blocatalytlc reaction with the electrocatalytlc detection of the liberated peroxide. The decrease In operating potential greatly benefits the amperometric monitoring of flowing streams. The attractive coupling of metal catalytic centers with carbon paste formulations should be very valuable for routine qualitative work.

No abstract