A fieldable process for sensitive detection of airborne viruses via electrophoresis-based RNA enrichment

Sensitive on-site virus detection is a requirement for timely action against the spread of airborne infection since ultra-low in-air viral concentrations can readily infect individuals when inhaled. Here, we consider a fieldable biosensing process that incorporates a fast RNA enrichment step in order to concentrate viral RNA in a small volume prior to RT-qPCR. The enrichment approach uses electrophoresis in an RT-qPCR-compatible buffer, and allows for concentration of RNA by nearly 5-fold within only 10 min. In order to place this performance into context, we analyzed the minimum detectable concentration of a low-cost, fieldable, biosensing process that uses electrostatic precipitation for air sampling, heating for viral RNA extraction, and then RNA enrichment, followed by RT-qPCR. With enrichment, we estimated an in-air concentration of 5,654 genome copies (gc)/m${}^3$ with a 100% detection rate and an in-air concentration of 4,221 gc/m${}^3$ with a 78.6% detection rate. Given that the concentrations of common viruses, such as influenza and SARS-CoV-2, in several indoor spaces are between 5,800 and 37,000 gc/m${}^3$, we conclude that enrichment allows a detection that is sufficiently sensitive for practical applications.