Design and development of an electrostatic sampler for bioaerosols with high concentration rate

Abstract

Integration of bioaerosol sampling methods with modern analysis techniques, such as the polymerase chain reaction as well as our ability to detect low concentrations of airborne agents require samplers that are able not only to efficiently collect the biological particles, but also to concentrate them in small amounts of fluids. In this research, we began development of a novel bioaerosol sampler, where a combination of electrostatic collection mechanism with superhydrophobic (“Lotus leaf” type) collection surface allows for efficient particle collection, removal and concentration in water droplets as small as 5 μL. This new sampling concept allowed achieving very high sample concentration rates (up to 1 million and higher) and could be applied to detect low concentrations of bioaerosols in various environments. The prototype electrostatic precipitator with superhydrophobic surface had a shape of a half-pipe, where a top plate served as the ground electrode, while the collecting surface was 3.2 mm wide rectangular electrode coated with a superhydrophobic substance and positioned in a groove in the flat bottom surface. Airborne particles drawn into the sampler were positively charged and then by the action of an electrostatic field deposited onto the negatively charged electrode. The sampler was positioned at a ∼1° inclination angle to the horizontal, and the injected water droplets rolled off of electrode's surface removing deposited particles. Sampler's performance has been analyzed with polystyrene latex particles of five aerodynamic diameters (0.5, 1.2, 1.9, 3.2, and 5.1 μm), collecting droplet volumes ranging from 5 to 60 μL, and sampling flow rates of 2, 5, and 10 L/min. It was determined that vast majority of particles deposited onto the electrode are removed by the first rolling droplet, which for 3.2 μm particle and 20 μL droplet translated into a concentration rate of 3×10 5. By narrowing the electrode to 2.1 mm and lowering the droplet volume to 5 μL we achieved the concentration rate as high as 1.2×10 6. These concentration rates were sustained for sampling times as long as 60 min. This novel sampling concept demonstrates a great potential for sampling and detecting airborne microorganisms in low concentration environments.