Rapid detection of SARS-CoV-2 using a radiolabeled antibody

Infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of coronavirus 2019 disease (COVID-19), poses a serious risk to humanity and represents a huge challenge for healthcare systems worldwide. Since the early days of the COVID-19 pandemic, it has been evident that adequate testing is an essential step in limiting and controlling the spread of SARS-CoV-2. Here, we present an accurate, inexpensive, scalable, portable, and rapid detection kit to directly detect SARS-CoV-2 in biological samples that could even be translated for population testing. We have demonstrated that our method can reliably identify viral load and could be used to reach those fractions of the population with limited access to more sophisticated and expensive tests.

The proposed SARS-CoV-2 detection kit is based on the combination of a SARS-CoV-2-targeted antibody (CR3022) that targets spike protein S1 domain on the viral surface. This antibody was radiolabeled with a long-lived isotope (Iodine-125) to allow us to detect bound antibody in samples with SARS-CoV-2. We used a series of in vitro assays to determine sensitivity and specificity and facilitate automation of the testing kit. Bound antibody was extracted from saliva samples via a centrifugation step and a semi-permeable membrane. Our kit was further validated using SARS-CoV-2 virions.

We were able to accomplish radiosynthesis of [¹²⁵I]I-CR3022 reliably without loss of binding. The SARS-CoV-2-sensing antibody was shown to maintain its spike S1 affinity and to bind to as low as 2.5-5 ng of spike protein. We then used beads-bound spike S1 to develop a separation kit which proved to be both easy to use and inexpensive. The kit made it possible to extract bound antibody from the saliva-like sample. We were able to validate the separation kit using intact SARS-CoV-2 virions and showed that our kit can detect a viral concentration as low as 19,700 PFU/mL (~ 9.22%TBF) and as high as 1,970,000 PFU/mL (45.04%TBF).

Here we report the development and validation of a SARS-CoV-2 detection system based on the combination of a specific radiolabeled antibody and a separation membrane. We demonstrate our system to be comparable to other SARS-CoV-2 detection kits already approved by the FDA and believe this technology could be easily deployed to countries with limited resources for the diagnosis of COVID-19. Furthermore, workflows could be easily adapted to target other antigens and therefore other types of diseases.