Plasma-activated CNT nanofluid aerosols for spray-based surface bacterial inactivation

The recent pandemic has underscored the need for better ways for surface disinfection of pathogens. Given the effectiveness of both plasma-activated water and carbon nanotubes (CNTs) for bacterial inactivation, we demonstrate in this work the production of stable plasma-activated CNT nanofluids using ultrasound—at relatively low power (70 W), short sonication time (6 min), and without requiring surfactants—to generate plasma-activated CNT nanofluids, which we subsequently aerosolize using a nozzle-free surface acoustic wave nebulizer. Besides providing better and more uniform surface coverage, such aerosolized delivery also allows for bacterial contact on uneven or hard-to-reach surfaces. For plasma-activated water with an electrical conductivity of 0.1 mS/cm, stable CNT nanofluids (lasting >72 h) are achievable by increasing the multi-walled carbon nanotube concentration to 0.006%. The effectiveness of the synergistic combination of plasma-activated water and CNT bacterial inactivation in an aerosolized delivery modality can be seen from the enhancement in bacterial colony count reduction—up to Δηe≈ 189%—when plasma-activated CNT nanofluid aerosols are sprayed onto E. coli plated agar plates, compared to that obtained with plasma-activated aerosols alone.