Optical electrodes

Some electrochemically active substances that can generate photons on an electrode surface are suitable labels for homogeneous immunoassays. A labelled antigen exhibits an electrochemical reactivity and produces luminescence, but when it is immunochemically complexed, the labelled antigen loses its electrochemiluminescent properties. One optical immunosensor for homogeneous immunoassays was assembled by spattering platinum on the end surface of an optical fibre. Spattered platinum maintains optical transparency and functions as an electrode. An optical electrode efficiently... 

A fiber-optic electrode was fabricated for the simultaneous generation and transmission of electrochemical luminescence by preparing a transparent electrode on the optical and surface of a fiber-optic. The opto-electrochemical properties of the micro-optical device were characterized in solutions containing the compounds required for luminol luminescence. The validity of sensitive measurement of electrochemiluminescence to be employed in a homogeneous immunoassay was evaluated by using potential step excitation of luminol in the presence and in the absence of hydrogen peroxide. 

In order to improve the sensitivity of the homogeneous immunoassay we have developed a Gber-optic electrode for the efficient generation and transmission of photons, and we have exploited luminol which has a much higher quantum efficiency than pyrene as a candidate for an electrochemiluminescent probe. 

Spectroelectrochemistry, a combination of optical spectroscopy and electrochemistiy has provided a powerful means for eluddating complex redox processes near solution-ekcbodc interfaces f 15.161. A union of transparent electrodes with fiber-optics provides a new strategy for designing new biosensing devices, provided they can be assembled into one instrument (fiber-optic electrode) that will generate and transmit a luminescence signal in response to the substance to be determined. 

We report here the performance characteristics of the fiber-optic electrode by app iqg the device to the electrochemiluminescence of luminol to clarify the feasibility of luminol as an electrochemiluminescent label for a sensitive homogeneous immunoassay. 

Fabrication of fiber-optic electrode. Platinom was sputtered on the flat end surface of a plastic fiber-optic (diameter 2 mm, length ISO cm) courteously supplied by Mitsubishi Rayon Co. Sputtering was performed by a Hitachi minisputter for 5 min at 15 mA. The platinum counter electrode was prepared as illustrated in Figure 2. The thin platinum layer for the working electrode was connected to a lead wire with silver paste, while that for the counter electrode was connected with solder. The contact points were then fixed in place and insulated by sealing with epoxy resin. 

Figure 2. Schematic illustration of the configuration of a fiber-optic electrode for the generation and simultaneous transmission of electrochemiluminescence.

AIZAWAETAL. Fiber-Optic Electrode for OptodeOrochenucol Biosensors 133... 

Figure 3. Experimental apparatus for the characterization of fiber-optic electrode.

The cell volume was less than 2 mL, therefore the potential of the fiber-optic electrode was referred to the reference electrode (Ag/AgCl) through a salt bridge. 

The fiber-optic electrode was employed for the oxidation of luminol. A phosphate-buffered solution (0.1 M, pH 70) was used as an electrolyte, and the scan rate was 5 mV/sec. 

The interval of a step-wise potential application for the excitation of luminol was also investigated. Figure 7 shows that a duration of the negative potential application of 5 s and that of the positive potential application of 15 s was the best conation for the greatest luminescence generation. Under the optimum condition, electrochemiluminescence of luminol was detected with the fiber-optic electrode in the concentration range from 10 to 10 3 M as shown in Figure 8. 

The metal oxo unit (M=0) is a fundamental constituent of both soluble molecular clusters and of complex solid materials. The practical interest in the molecular species reflects applications to homogeneous catalysis, heterogeneous catalysis, photocatalysis, electrocatalysis, magnetic materials, and materials synthesis. Likewise, the solid metal oxides exhibit a remarkable range of properties, with applications to high-temperature ferroelectrics, frequency doubling nonlinear optics, electrode materials in solid-state batteries, high-temperature superconductors, catalysis, sorption, and ceramics. 

Lantz J M and Corn R M 1994 Time-resolved optical second harmonic generation measurements of picosecond band flattening processes at single crystal TiO, electrodes J. Phys. Chem. 98 9387-90... 

The two essential elements of an electron spectrometer are the electrodes that accelerate electrons and focus them into a beam and the dispersive elements that sort electrons according to their energies. These serve the fimctions of lenses and prisms in an optical spectrometer. The same parameters are used to describe these elements in an electron spectrometer as in an optical spectrometer the teclmology is referred to as electron optics. 

The chaimel-flow electrode has often been employed for analytical or detection purposes as it can easily be inserted in a flow cell, but it has also found use in the investigation of the kinetics of complex electrode reactions. In addition, chaimel-flow cells are immediately compatible with spectroelectrochemical methods, such as UV/VIS and ESR spectroscopy, pennitting detection of intennediates and products of electrolytic reactions. UV-VIS and infrared measurements have, for example, been made possible by constructing the cell from optically transparent materials. 

Detector Detection in FIA may be accomplished using many of the electrochemical and optical detectors used in ITPLC. These detectors were discussed in Chapter 12 and are not considered further in this section. In addition, FIA detectors also have been designed around the use of ion-selective electrodes and atomic absorption spectroscopy. 

National Institute of Standards and Technology (NIST). The NIST is the source of many of the standards used in chemical and physical analyses in the United States and throughout the world. The standards prepared and distributed by the NIST are used to caUbrate measurement systems and to provide a central basis for uniformity and accuracy of measurement. At present, over 1200 Standard Reference Materials (SRMs) are available and are described by the NIST (15). Included are many steels, nonferrous alloys, high purity metals, primary standards for use in volumetric analysis, microchemical standards, clinical laboratory standards, biological material certified for trace elements, environmental standards, trace element standards, ion-activity standards (for pH and ion-selective electrodes), freezing and melting point standards, colorimetry standards, optical standards, radioactivity standards, particle-size standards, and density standards. Certificates are issued with the standard reference materials showing values for the parameters that have been determined. 

The principal uses of PCTFE plastics remain in the areas of aeronautical and space, electrical/electronics, cryogenic, chemical, and medical instmmentation industries. AppHcations include chemically resistant electrical insulation and components cryogenic seals, gaskets, valve seats (56,57) and liners instmment parts for medical and chemical equipment (58), and medical packaging fiber optic appHcations (see Fiber optics) seals for the petrochemical /oil industry and electrodes, sample containers, and column packing in analytical chemistry and equipment (59). 

Aluminum is best detected quaUtatively by optical emission spectroscopy. SoHds can be vaporized direcdy in a d-c arc and solutions can be dried on a carbon electrode. Alternatively, aluminum can be detected by plasma emission spectroscopy using an inductively coupled argon plasma or a d-c plasma. Atomic absorption using an aluminum hoUow cathode lamp is also an unambiguous and sensitive quaUtative method for determining alurninum. 

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