Induction Charging and Electrostatic Classification of Micrometer-Size Particles for Investigating the Electrobiological Properties of Airborne Microorganisms

Our earlier studies have shown that the electrostatic collection technique, a potentially "gentle" bioaerosol collection method, allows for efficient collection of airborne bacteria, but sensitive bacteria such as Pseudomonas fluorescens ( P. fluorescens ) lose their culturability during collection. We hypothesized that excessive stress was imposed on the sensitive bacteria by the sampler's conventional corona charging mechanism. In this research, we developed and built an experimental setup that allows us to analyze electrobiological properties of airborne microorganisms. In this experimental system, we imparted electric charges on airborne biological and nonbiological particles by aerosolizing them in the presence of an electric field. The charged P. fluorescens test bacteria and NaCl test particles were then channeled into a parallel plate mobility analyzer, which we have designed so that bacteria and inert particles carrying specific charge ranges can be extracted and made available for further analysis. When testing the experimental system, we related the extracted particle concentrations to the total particle concentration and obtained the charge distributions of these particles at different charging conditions. Our results have shown that even without charging, aerosolized P. fluorescens bacteria have a net negative charge and can carry up to 13,000 elementary charges per bacterium. In contrast, the NaCl particles were found to carry very few electric charges. We concluded that the electric charge carried by a bacterium consists of 2 components: its own natural charge, which can be high, and the charge imposed on it by the dispersion process. Our experiments have shown that the charge distributions on biological and nonbiological particles can be effectively manipulated by varying the external electric field during their aerosolization. Since airborne microorganisms may carry high internal electric charges, their collection by electrical field forces may be possible without first electrically charging them.