Many screening assays utilize probes such as antibodies or oligonucleotides supported or immobilized on a solid membrane. Membranes for these applications include nitrocellulose, nylon, PVDF and a range of other materials capable of binding probes. Common membrane assay formats include Western Blot, Northern and Southern Blot, Reverse Line Blot and others. Western blotting, first described in 1979, was the first method by which proteins separated by gel electrophoresis were transferred to a nitrocellulose membrane, which could then be probed with antibodies. With this procedure, the binding of antibodies to individual antigens in a complex mixture can be visualized. Western Blotting remains the standard confirmatory assay for HIV infection, and is used in testing many other disease conditions. Reverse line blot hybridizations, in which DNA probes are immobilized on a membrane in order to detect complementary targets in solution, were first described in the 1980’s. The wide range of applications include microbial identification assays, genetic tests and spoligotyping for TB strain identification.
Membrane assay procedures generally require multiple steps including incubations and washes, and a final substrate reaction to identify the binding of soluble targets in the sample to membrane-bound probes. Frequently, probes and test samples are in limited supply or very valuable. A means to reduce the volume of probe or sample used in the assay, while also enabling fast and efficient processing of multiple samples, is desirable. We have addressed this problem through development of a series of unique instruments for processing membrane assays, the Miniblotter® and MiniSlot™ systems.