Heat-induced fragmentation of airborne bacteria enables real-time concentration sensing

Abstract

Rapid measurement of airborne bacterial concentration is crucial in various fields, including bioaerosol research, indoor air quality management, and biosafety. Airborne bacteria contribute to indoor air quality deterioration, as certain bacterial species can cause health challenges such as respiratory infections and allergic reactions. We measured the concentration of airborne bacterial particles and electrical currents carried by the bacterial particles at room and high temperatures. Some S. aureus were fragmented into nano-sized (5-100 nm) particles at temperatures exceeding 300 degrees C for 3.7 s. At 400 degrees C, extensive bacterial fragmentation resulted in a substantial increase in electrical current compared to that at 20 degrees C. Moreover, number concentration and electrical current measurements were performed at room and high temperatures for Polystyrene Latex (PSL) particles, representing airborne particulate matter (dust). PSL particles did not undergo fragmentation at high temperatures, resulting in no difference in the electrical currents they carried at 20 degrees C and 400 degrees C. After observing the differences both in bacterial number concentration and electrical current between 20 degrees C and 400 degrees C, we introduced a methodology to predict the number concentration of airborne bacteria particles at 20 degrees C in real-time. For particle mixture (PSL: bacteria = 2.2) suspended at 20 degrees C, the airborne bacterial concentration was calculated by measuring the electrical current carried by the bacterial particles and comparing it to the current measured after exposure to 400 degrees C. The calculated bacterial concentration was 98.7 particles per 1 cm3 air, closely aligning with the measured bacterial concentration, 100.5 particles/cm3 (1.7% difference).