Two further important advantages of the graphite nonwoven erythrocyte retention substance result from its black color. After application of the blood onto a two-layer test system of the retention layer and reagent membrane, the red erythrocytes retained in the graphite nonwoven can scarcely still be detected visually, which is to be evaluated as an aesthetic advantage. This advantage also manifests itself in the reflectometric evaluation of the color reaction in the reagent membrane, because in contrast to the conventional systems (red-colored, erythrocyte-containing glass fiber layers as a background), no adverse reflectometric interferences can result.

The graphite nonwovens impregnated with known agglutinating agents, such as lectins, can be used as single- or multi-layer systems. In the case of multi-layer retention substrates, all or only individual graphite nonwoven layers can be impregnated with one or various agglutinating agents. Multilayer retention substances can also comprise other porous layers, such as polyvinyl alcohol nonwovens or monoor multi-filament woven fabrics, as elemental components, in addition to graphite nonwovens. It is essential only that the main content of the agglutinated erythrocytes is retained in a graphite nonwoven layer, and that preferably the top layer (application of blood) and the layer closest to the reagent membrane are made of graphite nonwoven.

Another typical property of the graphite nonwovens is their electrical conductivity, which is in the region of a few ohms typical of carbon fibers. As a result of the combination of electrical conductivity with the outstanding property of horizontal transportation of liquid, layers with bifunctional functions can be built up in respect to electrochemical sensor systems. In an amperometric test format, a graphite nonwoven layer can simultaneously perform the function of liquid-drawing microcapillaries, and simultaneously function as a reference electrode.

The worldwide market for blood-handling diagnostic test strips is huge. Diabetes testing represents only one type of strip. Test strips, by their nature, can be used only once. Many clinical tests require separating the serum or plasma from the whole blood; that is, filtering out the red blood cells (erythrocytes) from the remainder of the blood constituents. In particular, many diagnostic detection reactions cannot proceed accurately without first separating out and capturing the red blood cells so that the remaining constituents can be exposed to reagents deeper within the test strip.

This technology is offered by Bayer MaterialScience LLC. For more information, view the yet2.com TechPak at http://info.hotims.com/22930-154.

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