High-Throughput, Rapid, and Epitope-Specific Quantification of Neutralizing Antibodies Using Digital Nanoparticle Sensors

Project Summary/Abstract As of mid June 2021, the new coronavirus disease (COVID-19), caused by SARS-CoV-2 virus, has infected ~180 million people and causing ~3.8 million deaths globally. There are more than 34 million confirmed cases and ~620,000 deaths in the U.S alone. The fast transmission, asymptotic infection in some individuals, currently still limited supplies of vaccines in many countries, and constant virus mutation have made COVID-19 an unprecedented global threat to human health and economics. Neutralizing antibodies (nAbs) recognize SARS- CoV-2's spike protein and block cellular entry, acting as the first responders in the immune system towards pathogen clearance. Evaluating the effectiveness of nAbs against viral pathogens is important in understanding the level and duration of sterilizing immunity after natural infection or following vaccination, particularly given the rise of novel variants with vaccine escape potential. However, many of the available neutralizing assays used to assess nAb function involve propagation of viruses and thus require such assays be conducted in a biosafety level 3 (BSL3) lab settings, which, unfortunately, is unavailable to many researchers or clinicians. In addition, clinical laboratory-based antibody tests measure the total Ab level responding to SARS-CoV-2 antigens, without functionally evaluating pathogen-bound Abs and therefore cannot predict neutralizing activity. To bridge these technological gaps, we propose a multidisciplinary research plan to address the fundamental challenges in low- cost, high-throughput, fast, simple, and quantitative assay format in studying COVID-19 immune response. The investigators at ASU with complementary expertise in nanosensor design, antibody characterization, and coronaviruses will collaboratively develop a new and high-reward research strategy to establish a metal nanoparticle (MNP)-based nAb assay platform. This platform presents a few key features distinguishing it from previous technologies. First, the MNP assays are quantitative and accurate, with an expected dynamic range of 3 to 4 logs and a detection limit in the picomolar range. Further, this assay can be implemented in a rapid detection format without any washing steps, thus significantly simplifying its operation, reducing assay time to a few minutes, and making it feasible for mass-testing. Importantly, the assay is capable of detecting virus variants by targeted binding to the epitopes on the spike protein that are sensitive to mutations. Additionally, the readout can be performed in a well plate compatible with high-throughput screening with added portable electronic components, making the system automated in both detection and data analysis. We envision the employment of this rapid and quantitative nAb assay will also help timely determine the potential best uses of convalescent plasma and antibody treatment with future emerging novel viruses. Its low cost, simple operation, and automation capability are also very useful in longitudinal studies of the immune response related to COVID-19 infection, vaccination, and potential viral escape due to mutations. The nAb sensing can also be used for large-population sero-surveillance in determining the level of population-based immunity (herd immunity) against any virus strains.