Molecular tests such as reverse-transcription polymerase chain reaction (RT-PCR) is the clinical gold-standard method for laboratory diagnosis and can detect viral nucleic acids during the acute phase of infection, unlike serological methods based on human IgG and IgM [16,17]

Molecular tests such as reverse-transcription polymerase chain reaction (RT-PCR) is the clinical gold-standard method for laboratory diagnosis and can detect viral nucleic acids during the acute phase of infection, unlike serological methods based on human IgG and IgM [16,17]. (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 360A 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 360A 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 360A 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. == Introduction == The coronavirus disease 2019 (COVID-19) pandemic has resulted in an unprecedented public health crisis. As of October 2021, there have been approximately 245 million confirmed cases globally dealing devastating effects to economies and livelihood [13]. Individuals experiencing asymptomatic infection are a main source for the spread of COVID-19, with epidemiological and modeling studies estimating the number of cases to be more than 6 times greater than what is accounted for by surveillance systems [49]. As governments relax COVID-19 restrictions and societies begin to re-open, the ability to detect the disease as soon as it arises in communities is critical to maintaining low transmission levels. The etiologic agent of COVID-19 is severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The virus contains an enveloped single-stranded, positive-sense 30 kb RNA genome, which encodes structural proteins (membrane, M; envelope, E; spike, S; and nucleocapsid, N) and nonstructural proteins [10]. The viral membrane, consisting of M, E, and 360A S, surrounds a helical N, in which the viral genome is encapsulated by the N protein [11,12]. The S and N proteins of SARS-CoV-2 are produced and secreted at high concentrations in the oropharynx and nasopharynx during infection, making IL-11 them ideal diagnostic targets [13]. With the ongoing worldwide transmission of SARS-CoV-2 and emergent variants, there is a pressing need for large scale distribution of easily deployable, low-cost rapid tests. A multitude of diagnostic approaches have been developed throughout the course 360A of the pandemic, such as chest imaging, virus isolation, and molecular, serological, and antigen testing [14,15]. Molecular tests such as reverse-transcription polymerase chain reaction (RT-PCR) is the clinical gold-standard method for laboratory diagnosis and can detect viral nucleic acids during the acute phase of infection, unlike serological methods based on human IgG and IgM [16,17]. While RT-PCR tests often perform with high sensitivity and specificity, they require expensive instrumentation and reagents, experienced personnel, and have lengthy processing times [18]. As RT-PCR has failed to meet the global demands for rapid and early detection, recent studies have demonstrated that the frequency of testing, enabled by accessibility and turnaround time, should be prioritized for effective control of SARS-CoV-2 transmission [1922]. Rapid antigen tests address shortcomings of the aforementioned diagnostics and provide large-scale screening implications. Rather than detecting nucleic acids or human antibodies, antigen testing detects the viral proteins, allowing for detection of an active infection with relative ease of sample collection and assay. These rapid tests can be mass-produced at low cost and administered by the average person without a laboratory or instrumentation. These tests also take 15 minutes or less to determine the result, enabling real-time diagnosis and surveillance. In this paper, we demonstrate a robust antibody screening method to isolate murine monoclonal antibodies (mAbs) against SARS-CoV-2 S and N proteins. We then describe the development and validation of rapid antigen tests that use combinations of the mAbs, along with platinum nanoparticles, to detect SARS-CoV-2 with or without cross-reactivity to the genetically related severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1). Our.