Using Viral Aerosol Fluorescence to Aid Interpretations of Virus Inactivation: Application of Wideband Integrated Bioaerosol Sensor (WIBS)
ZHENYU MA, Herek L. Clack, University of Michigan
Abstract Number: 429
Working Group: Bioaerosols
Abstract
Introduction: Pathogenic bioaerosols, such as bacteria or virus particles, play an important role in affecting human health. To analyze these bioaerosols, fluorescence methods offer a high degree of specificity in target compound detection and analysis of certain fluorescent organic compounds. In this study, a wideband integrated bioaerosol sensor (WIBS) is used to analyze the fluorescence intensity of aerosolized viruses. After exposure to non-thermal plasma (NTP), producing conditions known to create reactive oxygen and nitrogen species and induce rapid virus inactivation, a decrease in the fluorescence of MS2 bacteriophage aerosol is observed. Simultaneous sampling has demonstrated the relationship between the decrease in aerosol fluorescence signal and the decrease of aerosolized virus infectivity.
Methods: The experimental setup consists of: a nebulizer (Mesh Nebulizer YM-3R9) that generates bacteriophage MS2 aerosols at 1 mL/min, a WIBS to detect changes in aerosol fluorescence, and a dielectric barrier discharge NTP reactor to inactivate aerosolized viruses. Bioaerosol fluorescence detection is performed by WIBS, manufactured by Droplet Measurement Technologies. In operation, WIBS is connected to sampling ports on the NTP reactor and samples aerosolized viruses before and after momentary plasma exposure. Aerosol fluorescence intensity at 310-400 nm is recorded for all particles during a 1-min sampling period after excitation at 280 nm. The NTP reactor generates plasma using an AC power supply (20 kV, 350 Hz) with an airflow rate through the reactor of 120 lpm. Upon collection of MS2 aerosol into impingers at both the inlet and outlet of NTP, samples are analyzed via plaque assay to quantify the infectious virus concentration. A plasma-power-off control is also performed to address any potential effect on infectivity assay and WIBS fluorescence measurements from the system.
Results: Aerosol fluorescence intensity at 310-400 nm, measured on a single-particle basis, is then plotted against the relative abundance of such particles to construct a ‘fluorescence distribution curve’. Results show that MS2 has a fluorescence distribution curve significantly distinct from the background, which measures the background particle fluorescence regardless of the detection of in-flow particles by WIBS. Its fluorescence decreases after exposure to NTP, whereas it remains constant when it passes through the powered-off NTP reactor. In addition to the fluorescence change, NTP exposure also led to a 1.05-log PFU/mL inactivation of MS2 aerosols, verified by plaque assay. Besides, by adjusting the plasma power, it is observed that the level of change of fluorescence signal also has a relationship with the inactivation level of MS2 aerosols.
Conclusions: The measured fluorescence of MS2 aerosols are found to correlate with their infectivity level. WIBS has the potential to provide information on fluorescent organics on the outer surface of bioaerosols, which would be helpful in understanding the virus inactivation process.