The challenge in characterizing nitrocellulose membranes for lateral-flow tests is devising methods that are reflective of the way that they are used. Lateral-flow membranes have pore sizes ranging from 3 to 20 ^m (10,11). Below this range, the lateral flow rate is too slow to be practical in this format. Above this range, it is currently technologically impossible to make the membranes. Many of the traditional methods used to characterize membranes reflect their use for liquid filtration. Pore-size rating and flow time are two such methods. Although they work well, their relevance to lateral flow is limited because the pore structure is being assessed through the plane of the membrane. These parameters may have no relationship to how the membrane performs as it is used in a lateral flow format, where liquid movement is parallel to the plane of the membrane. They also cannot be measured on backed membranes. The most important characteristics of lateral-flow membranes are capillary flow time, thickness, and surface quality.
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