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Biomedical subjects

S J Yao

Publications and source records attributed to S J Yao.

At least 19 recordsLinked to original sources
PubMed1991

Voltage polarity relay--optimal control of electrochemical urea oxidation.

Voltage polarity relay (VPR) is shown to optimize the urea oxidation rate and urea current utilization under constant current conditions in direct electrochemical urea oxidation. Direct electrochemical urea oxidation is characterized by reversible deactivation of the working electrode due to oxidation products remaining on the surface and the requirement that the working electrode potential remain below about 1.1 V relative to Ag/AgCl in order to prevent undesirable secondary electrochemical oxidations. The VPR method monitors the potential of the working electrode relative to a suitable reference and changes system polarity when the upper potential set limit is reached. Thus, what was the working electrode becomes the counter electrode and vice versa. Since urea oxidation products are desorbed from the counter electrode when its potential drops below about -0.6 V relative to Ag/AgCl, alternating electrode functions between working and counter provides cyclic electrode regeneration and continuous urea oxidation. VPR is believed to optimize constant current control for any electrochemical system that exhibits behavior similar to direct electrochemical urea oxidation.

Electrochemistry↗
PubMed1989

Electrochemical glucose sensing at low potentials.

An electrochemical sensing method was studied, employing cyclic voltammetry at smooth Pt-electrodes in the low potential region. It has certain advantages over methods that employ higher potentials or constant voltage amperometry. There are also advantages over methods employing active enzymes or other unstable elements. In addition to a specific scanning potential we have studied voltage-delay-pulsing techniques for electrode rejuvenation and innovative methods of creating analyte-selective covering membrane. At potentials below -0.6 V vs Ag/AgCl, peaks of adsorbed glucose species have been observed in cyclic voltammograms. These peaks at about -0.7 V (oxidation peak) and -0.8 V (reduction peak) have yielded reproducible current-glucose concentration relationships, linear through the region of clinically important glucose concentrations (50-300 mg/dl) and stable over time. Since these potentials are not in the redox range of many potentially interfering substances, selectivity is enhanced.

Biosensing Techniques↗
PubMed1987

Orbital reconstruction with proplast.

Proplast was implanted in 15 cases of orbital reconstruction. Seven cases were orbital floor fractures, four cases were phthisical enophthalmos, and four cases were anophthalmic enophthalmos. In orbital floor fracture cases, thin (2-mm) Proplast was placed onto the fractured orbital floor after the incarcerated orbital tissue was released. To correct the enophthalmic socket, Proplast was shaped into small pieces (10 x 5 x 2 mm), then inserted into the subperiosteal space from all directions to fill up the orbital cavity. The results of these 15 cases were satisfactory. The average follow-up period is 13 months. The increased orbital volume seems less than the volume of the implanted Proplast; therefore, we suggest an 80-90% overcorrection rate in accordance with the computer measurements. In sum, Proplast serves as a very good material for orbital floor reconstruction and volume replacement.

Adolescent↗
PubMed1984

Immobilized glucose oxidase in the potentiometric detection of glucose.

Previous work has shown that glucose oxidase can be immobilized on platinum to give an electrode that responds potentiometrically to glucose over the clinically useful range of about 10-250 mg glucose/100 mL. The present studies were carried out with electrochemically pretreated platinum and with gold or porous graphite substituted for the platinum support. The presence of the enzyme gave a significantly enhanced potentiometric response over that obtained with the bare support for both the pretreated platinum and the porous graphite, but not with gold. However, with platinum the potentiometric response became more negative with increasing glucose concentration. With porous graphite, the potential changed in the positive direction as the glucose concentration was increased. Hysteresis was demonstrated for the platinum-enzyme electrode. Mass transfer measurements with a rotating ring-disc electrode (RRDE) showed measurable diffusional resistances to the transport of a model electroactive compound (potassium ferrocyanide) through a matrix of immobilized enzyme attached to the disc of the RRDE. These results are part of a larger study to define the source of the potentiometric response by examining the roles of the support and the mass transfer resistances through the immobilized enzyme matrix.

Aspergillus niger↗
PubMed1979

Immobilized enzyme electrodes for the potentiometric measurement of glucose concentration: immobilization techniques and materials.

Glucose oxidase, catalase, and bovine serum albumin were co-immobilized with glutaraldehyde around a platinum screen or around a single platinum-iridium wire. The potential difference between this dual enzyme electrode and a Ag/AgCL reference electrode was proportional to the logarithm of the glucose concentration over the range from 10 to about 150 mg glucose per 100 ml in buffered solution at pH 7.4 and 37 degrees C. The enzyme electrode responded in serum only if coated with a semipermeable film, such as cellulose acetate, to exclude serum macromolecules. The potentiometric results were similar to those obtained with the two enzymes co-immobilized in polyacrylamide gel around a platinum screen or with only one of the enzymes, glucose oxidase, covalently coupled to a platinum screen. The results so far suggest that glucose for development of a continuous in vivo glucose sensor.

Catalase↗
PubMed1976

Hyaluronidase-bound membrane as a biomaterial for implantable fuel cells.

A new biomaterial containing covalently bound hyaluronidase was prepared. An application of this enzyme membrane is to improve the performance of an implantable fuel cell. Hyaluronic acid is a contributor to the viscosity of tissue fluids but can be a potential fuel source because of its sugar content. The incorporation of immobilized hyaluronidase would not only contribute to a more available fuel supply by splitting hyaluronic acid but, perhaps more importantly, enhance the rate of mass transport of fuel, O2, and reaction products by reducing the viscosity near the electrode membranes. Hyaluronidase was bound to Sepharose gel and its thermoplastic membrane after activation by cyanogen bromide. Fourteen and 22% of the activities were recovered from the gel and membrane, respectively. The activity of the bound enzyme was stable for six months at 0 degrees C. The addition of hyaluronic acid, 1 mg/ml, to a typical implantable type bioautofuel cell in vitro increased external solution viscosity from 1.1 to 2.5-2.8 cP and reduced voltage output under 10 komega by 60% in 3 hr. When the hyaluronidase bound membrane was placed at the anode, viscosity of the glucose-hyaluronic acid solution was lowered to 1.8 cP and the cell output increased to the original level of a glucose-fueled cell in 3 hr. Glucosamine-equivalent released from hyaluronic acid at the electrode was 3.1 mg after 22.5 hr. This represents 90% of the theoretical consumption. Restoration of the cell output was probably a combination of the enhanced transport of fuel, O2 and products, and/or appearance of a new fuel, glucosamine-equivalent.

Biocompatible Materials↗
PubMedDate not supplied

A thin-film glucose electrode system with compensation for drift.

Thin-film platinum electrodes have been prepared for use in a system for measurement of glucose. Cyclic voltammetry was used to test the electrodes in phosphate and bicarbonate solutions, and in the dialysate of human serum. The peak current output for glucose concentrations between 50-300 mg/dl in a phosphate buffer, and 100-250 mg/dl in the dialysate of human serum, were linear. Two of the three inflection points occurring in the voltammograms are invariant with changes in scan rate, pH, CO2, O2, and glucose. A method for using these points to compensate for voltage drift and current shift is discussed.

Blood Glucose↗
PubMedDate not supplied

A micro carbon electrode for nitric oxide monitoring.

A nitric oxide (NO) probe, consisting of a micro carbon fiber working electrode, 10 microns diameter, a platinum counter electrode, and a silver/silver chloride (Ag/AgCl) reference electrode, has been developed. The carbon fiber working electrode is covered with a Nafion cation exchange membrane. Using differential pulse voltammetry (DPV), we found the NO to N2O reduction current peak at approximately -1.35 V versus Ag/AgCl. This has been reported by others. The DPV current outputs are linearly related to dissolved NO concentrations [NO] in the 2-10 microM range. Catecholamines were found not to interfere with the reduction signal. The Nafion membrane also prevents interference by NO2-, NO3-, and amino acids at normal physiologic pH (pH 7.4). The effects of O2 are accounted for through sampling and subtracting background currents from the peak current. To increase sensitivity and shorten response time, a method of integrated pulse amperometry (IPA) was used for the study. The IPA charge outputs (delta C) are linear to the dissolved [NO] in the 50-350 nM range. The carbon fiber electrode has the potential of being miniaturized to a smaller electrode, allowing detection of NO released from the subendothelial space.

Carbon↗
PubMedDate not supplied

A microchip glucose sensor.

A major problem in development of a glucose sensor for use in an implantable artificial pancreas is the lack of reproducibility in signals from sensor to sensor. Each glucose sensor fabricated with currently used methods has a unique response to varying levels of glucose concentration and thus needs to be individually calibrated before use. We have adapted microchip manufacturing techniques for the fabrication of electrochemically based glucose sensors with standardized and reproducible function. Scanning electron microscopic study of the resulting electrode surfaces shows them to be smooth and featureless at all levels of magnification. X-ray diffraction analysis of the electrodes indicates preferential exposure of the [1,1,1] crystal interface. Cyclic voltammetry evaluation of initial sensor response to varying glucose concentrations shows excellent sensor to sensor reproducibility for all sensors made with the same underlayment. Sensors made with titanium underlayment appear to be more differentiated and thus more sensitive to variations in glucose concentration than are sensors with chromium underlayment. Although the initial response of microchip glucose sensors appears to be standardized and reproducible, additional development of an appropriate electrical insulation material is required before long-term study of signal stability is feasible.

Biomedical Engineering↗
PubMedDate not supplied

A nitric oxide sensor using reduction current.

Nitric oxide (NO) has a wide range of biologic activity. Methods commonly used for the detection of biologically derived NO are indirect and measure only the amount of NO released during an interval of time. An electrochemical method available is capable of being direct and continuous but is subject to interference. The recent explosion of scientific research into NO activity requires better methods of NO detection. This article reports a new NO electrochemical sensing method and sensor design. The tip of the sensor is covered with a hydrophobic membrane and contains an internal electrolyte. Platinum is used for the working and counter electrodes and silver/silver bromide (Ag/AgBr) for the reference electrode. The components of the internal electrolyte are potassium bromide and sulfuric acid. The NO that diffuses to the working electrode is first oxidized to NO+; the NO+ is reduced to NO; and the reduction current is determined. An integrated pulsed amperometric method is used to achieve the redox of NO and the measurement and integration of the reduction current. The results show that the NO sensor is sensitive and has a rapid response and less interference.

Biosensing Techniques↗