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  • 1
    Electronic Resource
    Electronic Resource
    From molecular recognition to analytical information using chemical sensors: Development of a combined catheter gastric pH-probe (1995)
    Weinheim : Wiley-Blackwell
    Electroanalysis 7 (1995), S. 859-863 
    Details
    ISSN: 1040-0397
    Keywords: Combined catheter gastric pH-probe ; Information theory ; Membrane technology ; H+-selective ionophores ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The best possible performance of a sensor can be described in terms of information theory according to Shannon, and is based on the reduction in entropy of a system. The relevant quantity is the maximum yield in information. The maximum yield in information can be related directly to the analytical performance and the selectivity of the recognition process. A combined catheter electrode for potentiometric intraluminal pH-measurement of 3 mm outer diameter was developed and tested in gastric juice. The sensor described is based on the neutral chromoionophore ETH 2418 incorporated into a liquid membrane of variable composition. The sensor was optimized to obtain maximum yield in information relevant to medical intragastric applications. The influence of different types of polymers, plasticizers, additives and carriers, and of varying their concentrations was studied. Studies focused on: extending the dynamic pH range; showing a sufficient pH-resolution and accuracy by eliminating the interference of the drug Dormicum. The combined catheter electrode showed a wide dynamic range, high long-term potential stability and good reproducibility, as well as a fast response time in aqueous solutions [15]. The maximum yield in information for 9 decades of H+-activity was calculated as to be 7.94 bits. The loss in information for one decade loss in dynamic range from 9 to 8 decades of H+-activity and constant reproducibility is 0.17 bits. This measure allows the comparison of required and achieved quality of different probes, accuracy not respected.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140070912
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  • 2
    Electronic Resource
    Electronic Resource
    Membraneless immobilization of xanthine oxidase on organic conducting salt/silicone oil electrodesDedicated to Prof. W. Simon. (1993)
    Weinheim : Wiley-Blackwell
    Electroanalysis 5 (1993), S. 869-876 
    Details
    ISSN: 1040-0397
    Keywords: Xanthine oxidase ; Hypoxanthine ; Tetrathiafulvalene ; Tetracyanoquinodimethane ; Enzyme electrode ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Xanthine oxidase (XOD, E.C. 1.2.3.2) has been immobilized on amperometric electrodes made from the organic conducting salt tetrathiafulvalene-p-tetracyanoquinodimethane (TTF-TCNQ) and silicone oil. Xanthine oxidase was immobilized by various techniques; immobilization by means of hydrophobic interaction was found to yield optimum analytical performance. Except for buffer, no coreactants are required for sensor operation. The response of the XOD electrode to its substrate hypoxanthine can be described by the enzyme-kinetic Michaelis-Menten formalism with excellent correlation (in most cases, Γ2 〉 0.995). Steady-state currents are usually measured within 10 seconds. Apparent KM (typically 3 to 10 μM) and saturation current values (0.2 to 3.7 μA, measured with new electrodes) strongly depend on the preparation procedure chosen as did the useful lifetime of the XOD sensors which was up to several weeks at room temperature. The described immobilization methodologies circumvent diffusion problems associated with well-established biosensor preparation techniques (e.g., physical entrapment in gel or between dialysis membranes) and thus yield biosensors of superior analytical performance.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140050923
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  • 3
    Electronic Resource
    Electronic Resource
    Kinetic studies on membraneless amperometric biosensors prepared from xanthine oxidase, organic conducting salt, and silicone oil (1994)
    Weinheim : Wiley-Blackwell
    Electroanalysis 6 (1994), S. 305-315 
    Details
    ISSN: 1040-0397
    Keywords: Xanthine oxidase ; Hypoxanthine ; Tetrathiafiulvalene ; Tetracyanoquinodimethane ; Rotating disk electrode ; Biosessor ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Membrane-free amperometric biosensors have been prepared from xanthine oxidase powder (XOD) (E.C.1.2.3.2) the organic conducting salt TF-TCNQ, and silicone oil The sensor response to hypoxanthine can be described by the ezyme-kinetic Michaelis-Menten formalism with good correlation over a wide range of potential (-100 tc +300 mV vs Ag/AgCl) and pH (6.10 to 8.80)values. Measurements with rotating disk rotating disk electrodes reveal that XOD is oxidized by at least two transfer to the mediators so that the sensor can be operated in air-saturated solution. Since open circuit conditions alter the kinetic parameters of the sensor, operation in flow analysis systems is recommended. Analytical features including response time (t95 ≈ 10 seconds), detection limit (ca. 10 nM hypoxanthine), selective over interferents (e.g., ascirbate), and simplicity of preparation as well as operation and storage stability compare very favorably with other OXD biosensors.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140060407
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