Electric field manipulated droplet encapsulation for airborne virus monitoring at indoor environmental levels

Abstract

Monitoring airborne viruses is crucial for mitigating the spread of infectious diseases. However, their low concentrations (< 10(4) RNA copies per 1 m(3) of air) make the monitoring challenging. The initial step is collecting a plenty of air and generating virus suspensions for subsequent analyses. The enrichment capacity (EC) indicates how many airborne viruses can be accumulated in a liquid sample. In this study, we present an electrowetting-assisted (EWA) electrostatic sampler that collects airborne viruses onto a hydrophobic surface and encapsulates them into a single droplet, thereby enhancing the EC by reducing the liquid sample volume from mL to mu L scale. After electrostatic sampling and subsequent droplet actuation, the virus sampling performance was evaluated at indoor environmental levels (10(2) similar to 10(5) RNA copies/m(3)). Polymerase chain reaction (PCR)-detectable samples were collected within an air-sampling duration of 20 min. The minimum PCR-detectable airborne virus concentration was determined to be 150 RNA copies/m(3), surpassing reference samplers that are ineffective at low airborne virus concentrations or require prolonged sampling durations. Field tests in indoor environments such as classroom, cafeteria, and corridor confirmed reliable airborne virus detection. The proposed approach has the potential to enhance real-time airborne virus monitoring and early risk evaluation in public indoor environments.