The Use of Nitrocellulose Membranes in Lateral-Flow Assays

Microporous nitrocellulose membranes are used in lateral-flow assays as the substrate upon which immunocomplexes are formed and visualized to indicate the presence or absence of an analyte in a liquid sample. The pore sizes of membranes used in this application are comparatively large, ranging from 3 to 20 μm. Several attributes have resulted in nitrocellulose being the preferred substrate for lateral-flow assays. First, nitrocellulose adsorbs protein at a high level. Second, chemistries that make the membrane wettable with aqueous solution do not significantly diminish protein adsorption. Third, nitrocellulose membranes can be cast that have pores sufficiently large to allow lateral flow of fluid in a reasonable time. To facilitate the utilization of nitrocellulose in lateral-flow assays, the membrane can be cast directly onto a polyester backing. The backing does not interfere with the function of the nitrocellulose while significantly improving its handling properties. Optimal performance of nitrocellulose membranes requires an understanding of the interactions of test reagents with the nitrocellulose and the effects of reagent location on assay sensitivity.