The Use of LIF-based Instrument with 405 nm for Real-time Monitoring of Aerosolized Bio-particles

Abstract

Bio-aerosols can affect public health depending on the origin of bio-particles (bacteria, virus etc.). Here, we attempted to assess the applicability of laser-induced fluorescence (LIF) instrument with 405 nm to real-time monitoring of bacteria and viruscontaining aerosols. For the purpose, the LIF-based BDS (Bio-aerosol Detection System) was used. The bio-particle monitoring of the BDS is based on fluorescence signals from two wavelength ranges [short wavelength range (SWR): 430–550 nm & long wavelength range (LWR): 500–600 nm] and the scattering signal. Firstly, auto-fluorophores (NADH, riboflavin, tyrosine, tryptophan) were tested to expect the monitoring ranges of the BDS for the auto-fluorophores. NADH and riboflavin showed fluorescence signals from two wavelength ranges, and the fluorescence efficiency of NADH was higher in the SWR than in the LWR and that of riboflavin was reversed. While tyrosine and tryptophan showed negligible fluorescence signals from two wavelength ranges as expected. Next, the lyophilized powders of Bacillus subtilis (BS), virus vaccines [ND (Newcastle Disease), IB (Infectious Bronchitis)] and the bacteriophage MS2 were tested to investigate the monitoring ranges of the BDS for the bio-particles. Individual virus and bacteriophage have been expected no fluorescence signals because of the absence of NADH and riboflavin fluorescing by 405 nm. Nonetheless, all the tested samples showed the fluorescence signals in the size range of 2 to 15 μm, generally known as bio-aerosol size. Considering that atmospheric virus particles are released through the respiratory organs of their hosts, just as virus vaccines from chicken embryo and MS2 from E. coli, it can be thought in turn that the BDS can also monitor bio-aerosols including virus as well as bacteria. Taken together, we suggests that the BDS, LIF-based instrument with 405 nm, is applicable for real-time monitoring of virus-containing aerosols as well as other bio-aerosols by counting the fluorescence particles and resolving their particle sizes.

Recent advancements in the measurement of pathogenic airborne viruses

“…Dead viruses (with and without intact DNA), cell fragments or proteins No reports on viral aerosol detection ( Ghosh et al, 2015c , Ghosh et al, 2015b ) Fluorescence based quantitative analysis Flow cytometry ( Lippe, 2018 ) Mass spectrometry MALDI-TOF plaque forming and non-plaque forming infectious viruses, dead and fragments Compounds less than 600 Da in size cannot be detected No reports on viral aerosol detection ( Cardozo et al, 2020 ) Optical ATP bioluminescence Cannot be used for any state of viruses applicable to bacteria, fungi, and mycoplasma This method is based on auto-fluorophores of bio-particles such as NADH etc., and metabolic activity markers such as ATP. ( Yoon et al, 2019 , Su et al, 2020 ) UVAPS Cannot be used for virus detection Only applicable to viable bacteria & fungi …”

“…Viruses contain small amounts of auto-fluorophores (tryptophan and tyrosine) that do not fluoresce by 405 nm light, while the main sources of fluorescence, NADH and riboflavin, are absent in individual viruses ( Hill et al, 2013 ). Therefore, auto-fluorophore-based detection methods are not suitable for detection of airborne virus particles ( Yoon et al, 2019 ). UVAPS, one of the most well-known equipment using LIF, is used for real-time detection of viable bioaerosols by measuring the fluorescence signals in the size range of 0.5–15 µm using ultraviolet (UV) laser excitation at 355 nm and emission in the range of 420–575 nm ( Xu et al, 2011 , Uk Lee et al, 2010 ).…”