Disposable electrodes

Although at present these biosensors cannot be considered as an accurate quantification technique, the applicability as tools for a first and extremely useful screening of the toxicity of real environmental samples is demonstrated. The simplicity of both the biosensor construction and the electrochemical measurement, together with the electrode disposability and the sufficient sensitivity, make the amperometric biosensors attractive for routine analysis, even at home. 

Commercially available electrotransport systems are bulky and limited to acute appHcations (96). One example, the Drionic system used for the treatment of hyperhidrosis (excessive perspiration), is presoaked in water for 30 min before each 20- to 30-min treatment. Another system, the Phoresor, approved for the deHvery of Hdocaine [137-58-6] for local anesthesia, and of dexamethasone [50-02-2] for treatment of local inflammation such as bursitis or tendinitis, is powered by a 9 V replaceable battery and features a disposable, fiHable dmg electrode. 

There have been a number of cell designs tested for this reaction. Undivided cells using sodium bromide electrolyte have been tried (see, for example. Ref. 29). These have had electrode shapes for in-ceU propylene absorption into the electrolyte. The chief advantages of the electrochemical route to propylene oxide are elimination of the need for chlorine and lime, as well as avoidance of calcium chloride disposal (see Calcium compounds, calcium CHLORIDE Lime and limestone). An indirect electrochemical approach meeting these same objectives employs the chlorine produced at the anode of a membrane cell for preparing the propylene chlorohydrin external to the electrolysis system. The caustic made at the cathode is used to convert the chlorohydrin to propylene oxide, reforming a NaCl solution which is recycled. Attractive economics are claimed for this combined chlor-alkali electrolysis and propylene oxide manufacture (135). 

Moreover, disposable electrochemical sensors for the detection of a specific sequence of DNA were realised by immobilising synthetic single-stranded oligonucleotides onto a graphite or a gold screen-printed electrode. Tire probes became hybridised with different concentrations of complementary sequences present in the sample. 

Cadmium presents an environmental risk. Since small nickel-cadmium cells are often not separately disposed of, they may enter municipal garbage incinerators. The search for alternative materials for the negative electrode led to metal hydrides, which not only are regarded as environmentally less critical, but also allow higher energy density than cadmium. This is especially important for use in portable equipment, such as cellular phones or lap-... 

Microfabrication technology has made a considerable impact on the miniaturization of electrochemical sensors and systems. Such technology allows replacement of traditional bulky electrodes and beaker-type cells with mass-producible, easy-to-use sensor strips. These strips can be considered as disposable electrochemical cells onto which the sample droplet is placed. The development of microfabricated electrochemical systems has the potential to revolutionize the field of electroanaly-tical chemistry. 

Nickel-cadmium batteries are rechargeable because the nickel and cadmium hydroxides products adhere tightly to the electrodes. More than 1.5 billion Ni-Cd batteries are produced every year. These batteries are not without drawbacks, however. Cadmium is a toxic heavy metal that adds weight to the battery. Moreover, even rechargeable batteries degrade eventually and must be recycled or disposed of in a benign way. 

The electrolyte was a solution of ammonium chloride that bathed the electrodes. Like Plante s electrochemistry of the lead-acid battery, Leclanche s electrochemistry survives until now in the form of zinc-carbon dry cells and the use of gelled electrolyte.12 In their original wet form, the Leclanche electrochemistry was neither portable nor practicable to the extent that several modifications were needed to make it practicable. This was achieved by an innovation made by J. A. Thiebaut in 1881, who through encapsulating both zinc cathode and electrolyte in a sealed cup avoided the leakage of the liquid electrolyte. Modern plastics, however, have made Leclanche s chemistry not only usable but also invaluable in some applications. For example, Polaroid s Polar Pulse disposable batteries used in instant film packs use Leclanche chemistry, albeit in a plastic sandwich instead of soup bowls.1... 

K.A. Joshi, J. Tang, R. Haddon, J. Wang, W. Chen, and A. Mulchnadani, A disposable biosensor for organophosphorus nerve agents based on carbon nanotubes modified thick film strip electrode. 

Another approach described above, which was employed by Meyerhoff s group [41], requires a set of identical electrodes, in which every electrode is disposed after a single measurement. A typical heparin-protamine titration requires on the order of 10-12 disposable electrodes. 

FIGURE 54 A schematic of hie flow-through immunosensor equipped with (1) fluid inlet, (2) carbon current collector, (3) disposable immuno-column, (4) highly dispersed antibody-modified carbon particles (immunosorbent), (5) carbon counter electrode, (6) Ag AgCl reference electrode and (7) fluid outlet. (Reprinted from [16] with permission from Elsevier.)... 

F. Darain, S.-U. Park, and Y.-B. Shim, Disposable amperometric immunosensor system for rabbit IgG using a conducting polymer modified screen-printed electrode. Biosens. Bioelectron. 18, 773—780 (2003). 

S. Centi, S. Laschi, M. Franek, and M. Mascini, A disposable immunomagnetic electrochemical sensor based on functionalized magnetic beads and carbon-based screen-printed electrodes (SPCEs) for the detection of polychlorinated biphenyls (PCBs). Anal. Chim. Acta 538, 205—212 (2005). 

Such electrodes should be sufficient as a reference electrode for short-term usage or as a disposable electrode. However, the requirement of a pre-hydration time may limit its applications for fast measurements, such as POCT (the point-of-care testing), due to its slow response time. In fact, the lack of long-term stable microreference electrodes will continue to hamper the development of integrated pH sensing systems. 

S. Kruger, S. Setford, and A. Turner, Assessment of glucose oxidase behaviour in alcoholic solutions using disposable electrodes. Anal. Chim. Acta 368, 219-231 (1998). 

L. Authier, C. Grossiord, P. Brossier, and B. Limoges, Gold nanoparticle-based quantitative electrochemical detection of amplified human cytomegalovirus DNA using disposable microband electrodes. Anal. Chem. 73, 4450-4456 (2001). 

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