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Background: The focus on laboratory-based diagnosis of coronavirus disease 2019 (COVID-19) warrants alternative public health tools such as rapid antigen tests. While there are a number of commercially available antigen tests to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), all cross-react with the genetically similar SARS-CoV-1 or require an instrument for results interpretation. Methodology/Principal findings: We developed and validated rapid antigen tests that use pairs of murine-derived monoclonal antibodies (mAbs), along with gold nanoparticles, to detect SARS-CoV-2 with or without cross-reaction to SARS-CoV-1 and other coronaviruses. In this development, we demonstrate a robust antibody screening methodology for the selection of mAb pairs that can recognize SARS-CoV-2 spike (S) and nucleocapsid (N) proteins. Linear epitope mapping of the mAbs helped elucidate SARS-CoV-2 S and N interactions in lateral flow chromatography. A candidate rapid antigen test for SARS-CoV-2 N was validated using nasal swab specimens that were confirmed positive or negative by quantitative reverse-transcription polymerase chain reaction (RT-PCR). Test results were image-captured using a mobile phone and normalized signal pixel intensities were calculated; signal intensities were inversely correlated to RT-PCR cycle threshold (Ct) value. Conclusion/Significance: Overall, our results suggest that the rapid antigen test is optimized to detect SARS-CoV-2 N during the acute phase of COVID-19. The rapid antigen tests developed in this study are alternative tools for wide scale public health surveillance of COVID-19. Author summary: The delays in diagnostic testing and lack of proper surveillance during the COVID-19 pandemic have contributed, in part, to the unprecedented death toll and impediment to wellbeing. As asymptomatic individuals have contributed to a large portion of disease spread, improved public health tools for widespread screening are necessary to maintain low transmission levels. We developed new rapid antigen tests that can be administered in less than 15 minutes without instrumentation, offering potential for frequent asymptomatic screening at-home and for point-of-care use in high-traffic areas such as schools, hospitals, and airports. The SARS-CoV-2 monoclonal antibody screening methodology resulted in pairs with or without cross-reaction to SARS-CoV-1, offering new opportunities for public health tools such as wide scale surveillance. This paper provides important insights for nanoparticle-based immunochromatographic assays. [ABSTRACT FROM AUTHOR]