Compositions, methods and devices for the detection of anti-lipoidal antibodies and the diagnosis of disease, for example, syphilis, are described. In particular, a method for immobilizing a lipoidal antigen, comprising cardiolipin, lecithin, and cholesterol, on a solid support (such as a nitrocellulose membrane) is described. The ability to immobilize a lipoidal antigen on a membrane satisfies a long-felt need for a membrane-based assay for the detection of anti-lipoidal antibodies. Also described are immunoassay devices for concurrently performing treponemal and non-treponemal tests for syphilis.