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.

Core-shell nanostructures of Mn2O3@SiO2, Mn2O3@amino-functionalized silica, Mn2O3@vinyl-functionalized silica, and Mn2O3@allyl-functionalized silica were synthesized using the hydrolysis of the respective organosilane precursor over Mn2O3 nanoparticles dispersed using colloidal solutions of Tergitol and cyclohexane. The synthetic methodology used is an improvement over the commonly used post-grafting or co-condensation method as it ensures a high density of functional groups over the core-shell nanostructures. The high density of functional groups can be useful in immobilization of biomolecules and drugs and thus can be used in targeted drug delivery. The high density of functional groups can be used for extraction of elements present in trace amounts. These functionalized core-shell nanostructures were characterized using TEM, IR, and zeta potential studies. The zeta potential study shows that the hydrolysis of organosilane to form the shell results in more number of functional groups on it as compared to the shell formed using post-grafting method. The amino-functionalized core-shell nanostructures were used for the immobilization of glucose and L-methionine and were characterized by zeta potential studies.

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Enhanced functionalization of Mn2O3@SiO2 core-shell nanostructures

Design of luminescent lanthanide complexes: From molecules to highly efficient photo-emitting materials

Nanotechnology has opened new and exhilarating opportunities for exploring glucose biosensing applications of the newly prepared nanostructured materials. Nanostructured metal-oxides have been extensively explored to develop biosensors with high sensitivity, fast response times, and stability for the determination of glucose by electrochemical oxidation. This article concentrates mainly on the development of different nanostructured metal-oxide [such as ZnO, Cu(I)/(II) oxides, MnO2, TiO2, CeO2, SiO2, ZrO2, and other metal-oxides] based glucose biosensors. Additionally, we devote our attention to the operating principles (i.e., potentiometric, amperometric, impedimetric and conductometric) of these nanostructured metal-oxide based glucose sensors. Finally, this review concludes with a personal prospective and some challenges of these nanoscaled sensors.

/pdf/a-comprehensive-review-of-glucose-biosensors-based-on-ye0vz5ywv7.pdf

A comprehensive review of glucose biosensors based on nanostructured metal-oxides.

An optical-based sensor for detecting the presence or amount of an analyte using both indicator and reference channels. The sensor has a sensor body with a source of radiation embedded therein. Radiation emitted by the source interacts with indicator membrane indicator molecules proximate the surface of the body. At least one optical characteristic of these indicator molecules varies with analyte concentration. For example, the level of fluorescence of fluorescent indicator molecules or the amount of light absorbed by light-absorbing indicator molecules can vary as a function of analyte concentration. In addition, radiation emitted by the source also interacts with reference membrane indicator molecules proximate the surface of the body. Radiation (e.g., light) emitted or reflected by these indicator molecules enters and is internally reflected in the sensor body. Photosensitive elements within the sensor body generate both indicator channel and reference channel signals to provide an accurate indication of the concentration of the analyte. Preferred embodiments are totally self-contained and are sized and shaped for use in vivo in a human being. Such embodiments preferably include a power source, e.g. an inductor, which powers the source of radiation using external means, as well as a transmitter, e.g. an inductor, to transmit to external pickup means the signal representing the level of analyte.

Optical-based sensing devices

The subject of sol−gel electrochemistry is introduced, starting with a brief account of milestones in its evolution. Then, the types of sol−gel materials that are useful for electrochemistry are presented, followed by a description of recent advances in the various fields of sol−gel electrochemistry. Modified electrodes, solid electrolytes, electrochromic devices, and corrosion protection coatings are described. Emerging fields such as RuO2 supercapacitors and electrochemical synthesis of sol−gel precursors are also addressed.

Sol−Gel Materials in Electrochemistry

Sol-gel techniques can be used to make biosensors, waveguide sensors, and modified electrodes in a variety of configurations

Organically modified sol-gel sensors

Sol-gel electrochemistry is gaining popularity as a versatile general method for the production of inorganic-organic electrodes and electrochemical sensors. Carbon-ceramic electrodes constitute a fine example that demonstrates the disadvantages, capabilities and promise of sol-gel electrochemistry. The compositions, configurations and chemistry of carbon ceramic electrodes are reviewed. Application for diverse fields of electrochemistry, including electrochemical sensing, biosensing and energy storage cells are reviewed.

Sol-Gel Derived Composite Ceramic Carbon Electrodes

Electrochemical characterization and morphological studies of palladium-modified carbon ceramic electrodes

Graphite electrodes comprising silica binder were tested in ethylene carbonate‐dimethyl carbonate (EC‐DMC), propylene carbonate and tetrahydrofuran solutions. The electrochemical behavior of these electrodes was analyzed using chronopotentiometry, slow-scan rate cyclic voltammetry (SSCV), impedance spectroscopy and potentiostatic intermittent titration technique (PITT). The electrode morphology and integrity were studied by scanning electron microscopy (SEM). Using silica binder, graphite particles are usually embedded in the current collector in an unoriented form. Thus, the electroanalytical study of these electrodes and the comparison of their response with that of highly oriented PVDF based graphite electrodes, provided insight into the eAect of particle orientation on the general electrochemical behavior of lithiated graphite anodes. In general, the higher the particle orientation and compact packing in the electrodes’ active mass, the better the performance of the Li‐ graphite electrodes, as the surface films developed are better passivating and the interparticle electronic contact is also better. The silica binder may have advantages over other binders such as PVDF in its ability to better retain the electrode integrity upon cycling. However, the practical use of such electrodes requires further optimization, especially in connection with particle orientation and compact packing.

L. Rabinovich

Papers

Sol−Gel Materials in Electrochemistry

Organically modified sol-gel sensors

Sol-Gel Derived Composite Ceramic Carbon Electrodes

Electrochemical characterization and morphological studies of palladium-modified carbon ceramic electrodes

Behavior of lithiated graphite electrodes comprising silica based binder