# Rapid and Cost-Effective Diagnostic Blot Assays Based on the Use of Plant-Produced Recombinant Antigens: Lessons Learned from the SARS-CoV-2 RBD Antigen

## TL;DR

This paper describes a fast and affordable diagnostic test using plant-produced antigens to detect SARS-CoV-2, showing it works well and can be scaled up easily.

## Contribution

The study introduces a plant-based method for producing a high-quality SARS-CoV-2 antigen for rapid diagnostics, offering faster and cheaper production than traditional methods.

## Key findings

- The RBDw-Fc antigen was produced in Nicotiana benthamiana plants with high yield and purity.
- The blot assay using RBDw-Fc showed high sensitivity and specificity for detecting SARS-CoV-2 in clinical samples.
- The plant-based method outperforms traditional systems in speed, scalability, and cost efficiency.

## Abstract

The ongoing demand for reliable, cost-effective, and scalable diagnostic solutions during the COVID-19 pandemic emphasized the need for innovative production platforms. In this study, we present a plant-based molecular farming (PMF) strategy for the production of the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein fused with an Fc region (RBDw-Fc). The RBDw-Fc antigen was transiently expressed in the Nicotiana benthamiana plant, achieving high yields and purity. Its functionality was assessed through antigen–antibody binding assays. The purified antigen was subsequently employed in the development of a rapid diagnostic blot assay capable of screening plasma EDTA samples from pre- and post-vaccinated as well as pre- and post-infected individuals, demonstrating high sensitivity and specificity. Our results show that the RBDw-Fc-based assay is effective for SARS-CoV-2 detection and offers considerable advantages in terms of production speed, scalability, and cost efficiency compared to traditional systems, such as cell-culture-based production. The assay delivers accurate results in just a few minutes, making it particularly suitable for clinical and resource-limited settings. This study highlights the versatility of PMF as a platform for producing high-quality reagents, with promising applications beyond SARS-CoV-2 diagnostics. The RBDw-Fc antigen-based method provides a model for the rapid, economical, and flexible development of screening tools for emerging infectious diseases and future pandemics.