Elucidated benefit of nanogap cavities for point-of-care immunoassays. Integrated a sandwich immunoassay microarray within a plasmonic nanogap cavity resulting in a 151-fold increase in fluorescence and 14-fold improvement in the limit-of-detection for the cardiac biomarker B-type natriuretic peptide (BNP). (Nano Letters 20, 4330 (2020), Advanced Materials 35, 2107986 (2023)).