Sensor oxygen membranes

Oxide ion conductors have been extensively investigated for their applications in fuel cells, oxygen sensors, oxygen pumps, and oxygen permeable membranes [81-108], The ion conduction effect was discovered more than a century ago by Nernst in zirconia products [83,84], To use zirconia, it... 

Optical sensor Amperometric sensor Amperometric sensor Oxygen electrode/polysulfone membrane Platinum electrode Glassy carbon electrode/ methylene blue mediator Three separate enzyme electrodes of pH electrode/cellulose acetate membrane Platinum electrode... 

Oxygen concentration is determined electrochemically using a membrane oxygen electrode (Clark sensor). Oxygen is consumed by micro-organisms, and the reduction in oxygen consumption with time is a measure of biological activity. 

Figure 38. A schematic illustration of the enzymic glucose electrode based on the oxygen membrane sensor (1) a layer of immobilized glucose oxidase (2) semipermeable Teflon membrane (3) reference electrode (4) cathode.

Mitsubayashi et al. (2003) developed a wearable and flexible oxygen sensor with membrane structure, constructed using microfabrication techniques, and containing a nonpermeable sheet and a gas-permeable membrane with platinum- and Ag/AgCl-electrodes. The sensor device, applied to the skin surface of healthy male volunteers with no history of skin diseases, allowed the safe monitoring, by CV, of the transcutaneous... 

A lot of analytical techniques have been proposed in recent decades and most of them are based on enzymes, called dehydrogenases, which are not sensitive to oxygen and need cofactors such as NAD". The key problems which seriously hamper a wide commercialization of biosensors and enzymatic kits based on NAD-dependent enzymes are necessity to add exogenous cofactor (NAD" ) into the samples to be analyzed to incorporate into the biologically active membrane of sensors covalently bounded NAD" to supply the analytical technique by NAD -regeneration systems. 

For completeness it should be mentioned that some of the theoretical conclusions for SECMIT are analogous to earlier treatments for the transient and steady-state response for a membrane-covered inlaid disk UME, which was investigated for the development of microscale Clark oxygen sensors [62-65]. An analytical solution for the steady-state diffusion-limited problem has also been proposed [66,67]. 

Fig. 6.11. The schematics of experimental set-up to study emission of atomic oxygen. 1 — sensor of oxygen atoms 2 samples of reduced silver 3 shutter 4 weights to brake membranes 5 platinum filament to calibrate sensor against the concentration of oxygen atoms.

Following the discovery that the fluorescence of metalloporphyrins is strongly quenched by oxygen57, optical sensor membranes were developed that are suitable for phosphorescent sensing of oxygen58. Table 1 summarizes fundamental articles on optical sensors for oxygen until the year 2000. 

Other optodes have been developed and tested in-vivo, all of them using a fluorophore, the fluorescence of which is quenched by oxygen. In the intravascular sensor developed by CDI, previously described, a specially synthesised fluorophore, a modified decacyclene ( Lexc=385 nm, em=515 nm), is combined with a second reference-fluorophore that is insensitive to oxygen, and is incorporated into a hydrophobic silicon membrane that is permeable to oxygen. 

The first and very simple solid contact polymeric sensors were proposed in the early 1970s by Cattrall and Freiser and comprised of a metal wire coated with an ion-selective polymeric membrane [94], These coated wire electrodes (CWEs) had similar sensitivity and selectivity and even somewhat better DLs than conventional ISEs, but suffered from severe potential drifts, resulting in poor reproducibility. The origin of the CWE potential instabilities is now believed to be the formation of a thin aqueous layer between membrane and metal [95], The dominating redox process in the layer is likely the reduction of dissolved oxygen, and the potential drift is mainly caused by pH and p02 changes in a sample. Additionally, the ionic composition of this layer may vary as a function of the sample composition, leading to additional potential instabilities. 

The first enzyme biosensor was a glucose sensor reported by Clark in 1962 [194], This biosensor measured the product of glucose oxidation by GOD using an electrode which was a remarkable achievement even though the enzyme was not immobilized on the electrode. Updark and Hicks have developed an improved enzyme sensor using enzyme immobilization [194], The sensor combined the membrane-immobilized GOD with an oxygen electrode, and oxygen measurements were carried out before and after the enzyme reaction. Their report showed the importance of biomaterial immobilization to enhance the stability of a biosensor. 

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