Capture of airborne nanoparticles in swirling flows using non-uniform electrostatic fields for bio-sensor applications

Collection of biological particles is the first and critical step for any biological agent detection system. Towards our goal of capturing and detecting airborne biological entities in real time, here we investigate on the design of an electrostatic particle capture system. We report on the capture of airborne 100 nm diameter polystyrene nanoparticles as a model system, in swirling flows under non-uniform electrostatic fields with an electrospray aerosol generator and a homemade particle collector. The particle collector has five positive electrodes on the bottom and one large grounded electrode on the top. The nanoparticles coming into the collector were slowed down during their swirling and stayed in the collector long before leaving the collector. Silicon chips were placed on the bottom electrodes and the electrostatically captured particles were counted as a function of flow rates, electrode positions, bias voltages, and capture times by epifluorescent images and scanning electron micrographs (SEMs). Particles captured in the electrode at the center of the collector were much less than those on the surrounding four electrodes and 10-25% of the particles with negative charges entering the collector were captured on the bottom electrodes at a flow rate of 1.1 l/min and an applied potential of 2 kV. Particle capture increased with decreasing flow rates. We also simulated flow and electrical fields separately, and found the positional trends to be in good agreement with the measurements. This collector is well adaptable to integration with micro resonator devices and can be used for real-time monitoring of bioaerosols.