The COVID-19 pandemic has underscored the global need for widespread testing. While current gold standard diagnostics return accurate results, they require expensive lab equipment making them difficult to use in resource-limited settings where the burden of disease is greatest. The lateral-flow immunoassay (LFA) is suitable for point-of-care diagnosis in resource-limited settings, but it suffers from limited sensitivity and lack of quantitative results.In Chapter 2, we increase the sensitivity of the LFA by developing a 3D printed casing that incorporates the LFA, dehydrated signal enhancements reagents, and a buffer reservoir to detect SARS-CoV-2 N-protein in serum at concentrations as low as 0.1 ng/mL. In Chapter 3, we address the lack of quantitative results by integrating the conventional LFA with the anisotropic etching of gold nanorods (GNRs) to achieve a multicolor, semi-quantitative assay that can be interpreted by the naked eye to determine digoxin concentrations in a serum sample.