Technical noteApplication of UVAPS to real-time detection of inactivation of fungal bioaerosols due to thermal energy
Introduction
Fungal bioaerosols constitute a major component among environmental airborne microorganisms (Wu, Tsai, Li, Lung, & Su (2004), Yeo & Kim (2002)) Fungal bioaerosols are relevant to the occurrence of human diseases and public health problems associated with acute toxic effects, allergies, and asthma (Bush & Portnoy (2001), Cooley, Wong, Jumper, & Straus (1998), Gravesen (1979), Pieckova & Jesenska (1999), Stark, Burge, Ryan, Milton, & Gold (2003), Verhoeff & Burge (1997)). As concerns over bioaerosols including fungal bioaerosols grow, several control methods have been developed to inactivate bioaerosols. Ultraviolet (UV) irradiation (Riley, Knight, & Middlebrook, 1976), electric ion emission (Grinshpun et al., 2004), airborne silver nanoparticles (Lee, Yun, Ji, & Bae, 2008), and thermal energy treatment (Jung, Lee, Lee, Kim, & Lee (2009b), Lee & Lee (2006)) have been studied as means of controlling bioaerosols. In these studies for controlling bioaerosols, the measurement methods for assessing the viability of bioaerosols have followed the traditional process: sampling of bioaerosols into liquid and solid media, incubation for several hours to days, and colony enumeration. From this serial process, the viability of bioaerosols has been evaluated and inactivation effectiveness due to control methods has been tested.
The critical disadvantage of this traditional measurement method is that it takes a long time, at least 24 h or longer, for incubation and enumeration of viable bioaerosols. Considering that the motivation for operating control methods is to decrease the concentration of viable hazardous bioaerosols in important specific indoor environments during special operations, this long period for incubation is a major obstacle in developing control methods and applying various control methods to real environments.
Recently, it was found that fungal bioaerosols could be successfully monitored by an UVAPS in a real-time manner (Kanaani, Hargreaves, & Ristovski (2007), Kanaani et al. (2008)). The ultraviolet aerodynamic particle sizer spectrometer (UVAPS, model 3314, TSI, St. Paul., MN, USA) is a real-time monitoring equipment for bioaerosols. The UVAPS can detect concentration, size distribution, and fluorescence of particles with aerodynamic diameters ranging from 0.5 to 15 μm. In particular, the fluorescence signals of sampled airborne particles are related to the viability of living microorganisms. Viable cells of most organisms have natural autofluorescence due to biochemical fluorophores (e.g. nicotinamide-adenine dinucleotide (NADH), nicotinamide-adenine dinucleotide phosphate (NADPH), riboflavin). The fluorescence signals from viable bioaerosols are provided by exciting passing aerosol particles with an UV laser beam at a wavelength of 355 nm and detecting the fluorescence emission from 420 to 575 nm. The strongest advantage of the UVAPS is the fast response to passing aerosols. The UVAPS showed effectiveness in detecting several fungal bioaerosols such as Penicillium and Aspergillus niger with variation of age and environmental stresses (Kanaani, Hargreaves, & Ristovski (2007), Kanaani et al. (2008)).
If the UVAPS can be used in measurement of the effectiveness of control methods in inactivating viable bioaerosols, it can accelerate studies for control methods as well as provide capacity for swift reaction to dispersal of bioaerosols by means of various control methods. However, a question that needs to first be addressed is, if bioaerosols are inactivated in a short period of time – on the order of sub-seconds – by given control methods, can the UVAPS be applied to detect the death of the bioaerosols in a real-time manner? The purpose of this study is to address this question.
As a starting point for this research, we chose thermal energy as a control method. The application of thermal energy is a representative and effective means of decreasing the culturability of fungal bioaerosols (Jung et al., 2009b), which are highly resistant to environmental stresses. Our team recently reported that thermal energy could significantly change certain properties of fungal bioaerosols (Jung et al., 2009b). Thermal energy changes the particle size distributions and the surface morphology of fungal bioaerosols. The concentration of beta-glucan, a toxic component of fungal bioaerosols, was reduced by exposure of fungal bioaerosols to thermal energy. Thermal energy can decrease the viability of fungal bioaerosols under harsh conditions, and can kill almost all fungal bioaerosols in sub-seconds (Jung et al., 2009b).
Then, after the fungal bioaerosols are killed by thermal energy, can the UVAPS be applied to viability measurement of fungal bioaerosols? If the role of the UVAPS is to detect viable aerosols, it should not detect dead airborne microorganisms. In this study, we attempted to answer the aforementioned question under experimental conditions. The specific aim of this study is to investigate the application capability of the UVAPS with respect to detecting passing fungal bioaerosols, which are instantly (in sub-seconds) killed by thermal energy.
Section snippets
Experimental methods
Fig. 1 shows a schematic diagram of the experimental setup. The experimental system is similar to the setup of a previous study involving a thermal energy test against fungal bioaerosols (Jung et al., 2009b) except that the UVAPS is employed as a measurement apparatus. The experimental system consists of four components: (i) a generating system for fungal bioaerosols, (ii) an UVAPS, (iii) a sampling system for a viability culture test of fungal bioaerosols before and after exposure to the
Fluorescence signals from inactivated fungal bioaerosols
The UVAPS provides information on particle concentration, size distribution, and fluorescence of aerosol particles. The fluorescence signal is expressed in 64 channels of the UVAPS detection system. Channel 1 shows the concentration of particles with non-fluorescence. Channels 2 to 64 cover the aerosol particles with fluorescence; here, a higher channel number corresponds to higher fluorescence intensity. Fig. 2, Fig. 3 show three-dimensional graphs of the UVAPS detection system, displaying the
Acknowledgements
This work was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology (2010-0007615) of Republic of Korea, and the Korea Institute of Science and Technology.
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