We now turn our attention to the application of the plasmonic patch as a universal fluorescence enhancer in fluoroimmunoassays. A typical sandwich fluoroimmunoassay involves the following major steps: (i) capture of the target antigen by an immobilized antibody; (ii) binding of the biotinylated detection antibody to the captured antigen; and (iii) binding of fluorescently labeled streptavidin (Fig. 4a). We hypothesize that the addition of a plasmonic patch after the last step (i.e., binding of the fluorescently labeled streptavidin) can result in a large enhancement of the fluorescence intensity and significantly improve the limit-of-detection (LOD given by the average fluorescence intensity at zero concentration (blank) plus three times its standard deviation). To verify this hypothesis, we implemented a fluoroimmunoassay in a heterogeneous, solid-phase format by using a 96-well microtiter plate as a sampling platform, a standard assay format extensively employed in bioanalytical research and clinical diagnostics (Fig. 4a).