First-generation glucose biosensors relied on the use of the natural oxygen cosubstrate and the production and detection of hydrogen peroxide and were much simpler, especially when miniaturized sensors are concerned. More sophisticated bioelectronic systems for enhancing the electrical response, based on patterned monolayer or multilayer assemblies and organized enzyme networks on solid electrodes, have been developed for contacting GOx with the electrode support. Electrochemical biosensors are well suited for satisfying the needs of personal (home) glucose testing, and the majority of personal blood glucose meters are based on disposable (screen-printed) enzyme electrode test strips, which are mass produced by the thick film (screen-printing) microfabrication technology. In the counter and an additional “baseline” working electrode, various membranes (mesh) are incorporated into the test strips along with surfactants, to provide a uniform sample coverage. Such devices offer considerable promise for obtaining the desired clinical information in a simpler, user-friendly, faster, and cheaper manner compared to traditional assays. Continuous ex-vivo monitoring of blood glucose was proposed in 1974 and the majority of glucose sensors used for in-vivo applications are based on the GOx-catalyzed oxidation of glucose by oxygen. The major factors that play a role in the development of clinically accurate in-vivo glucose sensors include issues related to biocompatibility, miniaturization, long-term stability of the enzyme and transducer, oxygen deficit, short stabilization times, in-vivo calibration, baseline drift, safety, and convenience.

Electrochemical Glucose Biosensors

3.6.1. Polishing and Cleaning 2663 3.6.2. Vacuum and Heat Treatments 2664 3.6.3. Carbon Electrode Activation 2665 3.7. Summary and Generalizations 2666 4. Advanced Carbon Electrode Materials 2666 4.1. Microfabricated Carbon Thin Films 2666 4.2. Boron-Doped Diamond for Electrochemistry 2668 4.3. Fibers and Nanotubes 2669 4.4. Carbon Composite Electrodes 2674 5. Carbon Surface Modification 2675 5.1. Diazonium Ion Reduction 2675 5.2. Thermal and Photochemical Modifications 2679 5.3. Amine and Carboxylate Oxidation 2680 5.4. Modification by “Click” Chemistry 2681 6. Synopsis and Outlook 2681 7. Acknowledgments 2682 8. References 2682

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Advanced carbon electrode materials for molecular electrochemistry.

An analyte monitor includes a sensor, a sensor control unit, and a display unit. The sensor has, for example, a substrate, a recessed channel formed in the substrate, and conductive material disposed in the recessed channel to form a working electrode. The sensor control unit typically has a housing adapted for placement on skin and is adapted to receive a portion of an electrochemical sensor. The sensor control unit also includes two or more conductive contacts disposed on the housing and configured for coupling to two or more contact pads on the sensor. A transmitter is disposed in the housing and coupled to the plurality of conductive contacts for transmitting data obtained using the sensor. The display unit has a receiver for receiving data transmitted by the transmitter of the sensor control unit and a display coupled to the receiver for displaying an indication of a level of an analyte. The analyte monitor may also be part of a drug delivery system to alter the level of the analyte based on the data obtained using the sensor.

Analyte Monitoring Device And Methods Of Use

for each type of enzyme but in an opposite direction for each. The type III enzyme experiences an increase in apparent Km with increasing inosine concentration, while the type V enzyme shows a slight decrease in apparent Km at high inosine concentration. The most dramatic homogeneous effect is that of increasing inosine concentration upon the VmM values, however. For the type III enzyme, apparent VmiU! is reduced by nearly a factor of 2 but, for the type V enzyme, apparent Vma, decreases more than 7-fold. Such product inhibition reveals itself through longer response times in the immobilized enzyme electrodes. The results obtained in this study show that the potentiometric ammonia gas-sensing enzyme electrode does exhibit linear responses to substrate concentrations both above and below the Km value of the adenosine deaminase enzyme when sufficient enzyme is immobilized at the electrode surface. The BSA-glutaraldehyde cross-link provides for stabilization of the enzyme activity as shown by the observed electrode lifetime. Comparison of the homogeneous kinetic parameters with those obtained from the immobilized study reveals significant changes in the kinetic properties of the enzyme when it is immobilized, possibly resulting from conformational changes in the enzyme upon exposure to BSA and glutaraldehyde. The magnitude of the effect of addition of inosine on apparent Km and Vmax depends upon whether the enzyme is immobilized or free in solution. The apparent Km for the immobilized enzyme remained essentially constant upon addition of inosine, while the apparent Km for the homogeneous enzyme did show some variation but in opposite direction for the type III and V enzymes. In the construction of enzyme electrodes, it is desirable to obtain the highest (fastest rate) and lowest Km (greatest affinity) values possible. From the results of this study carried out at high enzyme levels it is apparent that type III adenosine deaminase would be the best choice for the construction of an immobilized enzyme electrode both from the point of view of apparent Km and Vmax values and from the less pronounced product inhibition effect on the type III enzyme compared to the Type V enzyme. Even in the absence of initial inosine, type III enzyme electrodes have faster response times than corresponding electrodes prepared with type V enzyme.

Ferrocene-mediated enzyme electrode for amperometric determination of glucose.

Introduction Technology for electrical power generation using enzyme catalysts, established four decades ago, has recently received increased attention associated with demand for micro-scale and implantable power supplies. The main challenges, namely the fragility of enzyme molecules, characteristic low current density, and poor fundamental understanding of redox biocatalysis, are currently being addressed from a variety of research perspectives, to take advantage of enzyme selectivity, low temperature and moderate pH activity, and manufacturability in small-scale devices. Such an effort benefits from four decades of multidisciplinary research in biosensors and related bioelectrochemical fields. This review paper summarizes the current state of enzymatic biofuel cell research in the context of foreseeable applications and assesses the future prospects of the technology. Emphasis is placed on device performance and engineering aspects, with a view toward practical portable power devices based on enzymatic biofuel cells. Research in biocatalytically modified electrodes, particularly for sensor applications, has provided a significant technological underpinning for current biofuel cell development. There exists significant overlap in technical requirements between sensors and biofuel cells, including chemical and mechanical stability, selectivity, and cost of materials. However, these two technologies diverge in the areas of current density, cell potential and stability. There exists extensive review literature in the area of biological fuel cells. Notably, Palmore and Whitesides summarized biological fuel cell concepts and performance up until about 1992. More recently, Katz and Willner discussed recent progress in novel electrode chemistries for both microbial and enzymatic fuel cells. We do not duplicate these valuable contributions, but instead focus on the strengths and weaknesses of state-of-art materials in the context of specific classes of applications, and point to areas where additional knowledge is currently needed to exploit biological fuel cells. With some exceptions, we focus on contributions made after 1992. Biofuel cells have traditionally been classified according to whether the catalytic enzymes were located inside or outside of living cells. If living cells are involved the system is considered to be microbial, and if not it is considered enzymatic. Although microbial fuel cells posses unique features unmatched by enzymatic cells, such as long-term stability and fuel efficiency, the power densities associated with such devices are typically much lower owing to resistance to mass transfer across cell membranes. Thus, microbial fuel cells are expected to find limited application in smallscale electronic devices. This review will focus on enzymatic biofuel cells. While such cells typically demonstrate reduced stability due to the limited lifetime of extracellular enzymes, and are typically unable to fully oxidize fuels, they allow for substantial concentration of catalysts and removal of mass transfer barriers and provide higher current and power densities, approaching the range of applicability to microand mini-scale electronics applications. Applications and Requirements The range of possible applications for biofuel cells may be broken down into three main subclasses: 1. Implantable power, such as micro-scale cells implanted in human or animal tissue, or larger cells implanted in blood vessels. 2. Power derived from ambient fuels or oxidants, mainly plant saps and juices, but extending to sewage and other waste streams. 3. Power derived from conventional fuels including hydrogen, methanol or higher alcohols. Classes 1 and 2 are closely related. The fuels available for implantable power, such as blood borne glucose or lactate, are ambient in the sense that they are present in a physiological environment in the absence of a fuel cell device. One major distinction between these two classes is that the ambient-fueled cell need not be implanted, and focuses on plantor waste-derived fuels, whereas the implantable cell focuses on animal-derived fuels and is present within the physiological system. Class 3 is unique in that this class competes with well-established conventional fuel cell technology. To a greater or lesser extent, all three classes share the fundamental technical requirements of high power density and high activity.

Enzymatic biofuel cells for implantable and microscale devices.

Electropolymerized 1,2-diaminobenzene as a means to prevent interferences and fouling and to stabilize immobilized enzyme in electrochemical biosensors

Alexander M. Yacynych

Papers

Electropolymerized 1,2-diaminobenzene as a means to prevent interferences and fouling and to stabilize immobilized enzyme in electrochemical biosensors

Immobilized enzyme chemically modified electrode as an amperometric sensor

Differential pulse voltammetric study of direct electron transfer in glucose oxidase chemically modified graphite electrodes

Polymer film chemically modified electrode as a potentiometric sensor

Cyanuric chloride as a general linking agent for modified electrodes: attachment of redox groups to pyrolytic graphite