Discriminative films, permselective

Access to the surface of amperometric biosensors can be controlled by coverage with an appropriate permselective film. Such coatings effectively exclude coexisting interferences, and thus greatly improve the selectivity and stability. Discriminative films based on different transport properties are described. Structural factors and fundamental interactions that govern the transport through such films are discussed. Future prospects are examined. 

The words essentially pore free" are extremely restrictive. Pores of even 10-50 A present at an area fraction of even 10 ppm can destroy the permselectivity of a membrane which must discriminate gas molecules with characteristic dimensions of 3-5 A. A significant advance in technology occurred when Monsanto introduced a process to posttreat asymmetric fibcR with a minuscule amount of highly permeable stop leak" material such as silicone mbber. This treatment eliminates most of the Knudsen and viscous contributions to flow through the membrane and produces a high-flux membrane with selectivity approaching that of true dense fiims. As demonstrated in the Monsanto patent on this matter, however, the coating appeaR to be less than perfect, since dense-film selectivities typically are not achieved but may be approached quite closely. Data from applications of this approach are shown in Table 20.1-2 for coated and uncoated fibera. ... 

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