A novel method for measuring the charge distribution of airborne microbes

A novel method for measuring bioaerosol charge distribution was investigated using electrostatic sampling and quantitative polymerase chain reaction (qPCR). Here, Bacillus subtilis var niger and Pseudomonas fluorescens were aerosolized and precipitated into different regions of two 96-well plates placed inside an electrostatic sampler. The concentrations of negatively charged bacteria in the air samples collected were quantified using qPCR, and the relevant bioaerosol charge levels were calculated using an equation developed in this study. Experimental results showed that B. subtilis var niger bioaerosols had wider charge distribution than P. fluorescens. For B. subtilis var niger, 93% of them carried a charge level of 13-42 units, 2% carried a charge level of 8-13 or lower, and 5% carried a charge level of 42-195 or higher. While for P. fluorescens, 99% of P. fluorescens aerosols carried a charge level of 14-34 elementary units. The indicative charge levels of bioaerosols collected at a certain point in the electrostatic sampling line largely depends on the particle size, bacterial species, electrostatic field strength, and the sampling flow rates for a given electrostatic sampler. In general, the trends for the charge levels here were similar to those obtained in previous studies. Use of qPCR technology in this study can distinguish between biological and non-biological particles collected. Thus, this avoided counting the non-biological particles in traditional bioaerosol charge measurements in which an optical particle counter is used. The developed technique here can be also used to analyze the charge levels for other types of bioaerosols.