Oxygen sensitive layers

Navarro-Villoslada F., Orellana G., Moreno-Bondi M.C., Vick T., Driver M., Hildebrand G., Liefeith K., Fiber-Optic Luminescent Sensors with Composite Oxygen-Sensitive layers and Anti-Biofouling Coatings, Anal. Chem. 2001 73 5150-5156. 

Experimental results of the DTEG with FejOj as an oxygen sensitive layer at 580°C (sensor from Fig. 7.18).The temperature modulation frequency was 0.312 Hz. Figure 7.19(a) shows the transient oxygen profile, (b) shows the absolute error of the thermopower,... 

Results of an iDTEG withYSZ as an oxygen sensitive layer. Note the almost nonexistent temperature dependence of the sensor signal. Reprinted from Roder-Roith etal. (2009) with permission from Elsevier. 

Room temperature ionic liquids are air stable, non-flammable, nonexplosive, immiscible with many Diels-Alder components and adducts, do not evaporate easily and act as support for the catalyst. They are useful solvents, especially for moisture and oxygen-sensitive reactants and products. In addition they are easy to handle, can be used in a large thermal range (typically —40 °C to 200 °C) and can be recovered and reused. This last point is particularly important when ionic liquids are used for catalytic reactions. The reactions are carried out under biphasic conditions and the products can be isolated by decanting the organic layer. 

Later on, such S-layer-based sensing layers were also used in the development of optical biosensors (optodes), where the electrochemical transduction principle was replaced by an optical one [97] (Fig. 10c). In this approach an oxygen-sensitive fluorescent dye (ruthenium(II) complex) was immobilized on the S-layer in close proximity to the glucose oxidase-sensing layer [97]. The fluorescence of the Ru(II) complex is dynamically quenched by molecular oxygen. Thus, a decrease in the local oxygen pressure as a result of... 

Figure 3. First fiber optic chemical sensor (from ref. [17] used for sensing oxygen). Alos shown is a cross-sedction of the fiber bundle used. 6 light source 9 photodectectors 16 chemically sensitive layer.

In the same way, a 6-well culture plate has been prepared in order to monitor gradients in the oxygen supply of engineered tissue samples over a 21 day period. Figure 8 shows the horizontal cross-section of a tissue and the resulting charts of different samples after different time periods. light-scattering particles (TiCh) had been added to the polymer mixture to increase the excitation efficiency within the sensitive layer [33]. 

The polyethylene membrane covered an electrochemical enzymatic biosensor. The construction scheme of the sensor is displayed in Fig. 25. The electrochemical basic electrodes consist of a platinum anode and a silver-silver chloride cathode. A thermally sensitive layer of glucose oxidase was localized directly on the anode surface and was covered by a 30-pm-thick hydrophobic polyethylene membrane. The biosensor for the detection of the glucose concentration is based on an enzyme (glucose oxidase)-cat-alyzed reaction of the analyte (glucose) and the subsequent electrochemical detection of a reaction product (electron current). A stoichiometric surplus of the coreactant oxygen has to be guaranteed. This is realized by the polyethylene membrane (membrane with analyte door ) controlling the glu-... 

With a proper understanding of the transport properties in such multilayered structures, the containers for use in sterilization processes can be appropriately designed. As an example in designing for such a situation, a mass balance on water permeating into or out of a multilayered structure can be made to estimate the amount of water which can affect the hydrophilic polymer. With this analysis, the time required to dry the water sensitive layer and return the container to ambient oxygen permeability values can be estimated. Assuming the transport of water in the multilayer configuration is limited by the outer layers, the water content (M) of the inner layer in a prescribed container can be described by ... 

Three methods have been described for three halogens, two based on fluorescence and one on absorption. In the first [87], the fluorescence of rubrene in polystyrene is quenched by traces of iodine. This method is nonselective and the optode is also sensitive to oxygen. In another sensor, naphthoflavone in solution in a material of the silicone or PVC type serves as a sensitive layer for free halides [88]. The absorption technique uses a fiber with a liquid CS2 core [89] to detect 10 ng of iodide using a S m long capillary cell with sample circulation. The Hber itself constitutes the active optode (total reflection in the liquid core). A comparison of optodes based on dynamic quenching of absorbed Rhodamine 6G by iodide was reported [90]. Three solid supports for immobilization were used PTFE tape, XAD resin beads and crushed XAD-4 resin. The limits of detection are 0.18-0.30 and 1.1 mM respectively. Some anions (eg. Cl , Br , CN ) interfere at the 1-M level. 

The sensor is highly specific for oxygen. No interferences were observed with nitrogen, carbon monoxide, dinitrogen oxide, methane, carbon dioxide, and noble gases. Covering the sensitive layer with silicone-rubber resulted in a 60% reduction of the quenching constant. 

The pH-sensitive chemistry consists of a cellulosic material to which hydroxypyrene trisulfonate (HPTS) is covalently bonded. The C02-sensitive material is a fine emulsion of a hydrogen-carbonate buffer (plus HPTS) in a two-component silicone. The oxygen-sensitive chemistry is simply a solution of chemically modified decacyclene (which is strongly quenched by oxygen) in a one-component silicone. To make it insensitive toward halothane (an inhalation narcotic), it is covered with a thin layer of black PTFE, which also serves as an optical isolation. The fluorescence intensities of the three sensing spots can be related to PO2, pH, and PCO2 via modified Stem-Volmer or Henderson-Hasselbalch algorithms. 

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