Development of a merry-go-round inspired automatic paper-based ELISA system for colorimetric detection of SARS-CoV-2

The ongoing global challenge posed by the COVID-19 pandemic necessitates innovative and accessible diagnostic solutions. In response, we developed a novel merry-go-round-inspired automatic paper-based ELISA system for colorimetric detection of SARS-CoV-2. The system features a unique rotational mechanism, where synchronized movements of gears and solenoids enable precise and sequential solution loading for key ELISA steps, including sample introduction, washing, detection antibody addition, and substrate reaction. This automation minimizes manual intervention while ensuring high precision. The paper-based ELISA (p-ELISA) chip incorporates a multi-layered design, including four reaction chambers for fluid handling, a one-way surge layer for efficient waste absorption, and amine-functionalized cellulose paper discs for covalent antibody immobilization. This design not only facilitates multi-sample processing but also enhances throughput and consistency. By combining this innovative chip with the automated loading system, all essential ELISA steps—sample loading, reagent dispersion, and colorimetric signal detection—are performed on a single platform. Smartphone-based imaging with RGB analysis is capable of semi-quantitative detection of antigen levels, providing a user-friendly and accurate colorimetric readout. In addition, the system is controlled via a smartphone app with voice recognition, making it accessible and easy to operate. This cost-effective and eco-friendly platform demonstrated high specificity for SARS-CoV-2 antigens, with a detection limit in the nanogram range, and was successfully validated with clinical samples and multiple variants. These features position the system as a robust and accessible diagnostic tool for addressing COVID-19 and other infectious diseases, particularly in resource-limited settings.