Gentle Sampling of Submicrometer Airborne Virus Particles using a

Oct 27, 2016 - ... numerical collection efficiencies in the EPC and DF-ESP; procedure of qPCR assay; measured size distributions of nebulized MS2 and ...
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Gentle Sampling of Submicrometer Airborne Virus Particles using a Personal Electrostatic Particle Concentrator Seongkyeol Hong,† Jyoti Bhardwaj,‡ Chang-Ho Han,† and Jaesung Jang*,†,‡ †

School of Mechanical and Nuclear Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea ‡ Department of Biomedical Engineering, UNIST, Ulsan 44919, Republic of Korea S Supporting Information *

ABSTRACT: Measurements of airborne viruses via sampling have been critical issues. Most electrostatic samplers have been assessed for bacterial aerosols or micrometer-sized viral particles; however, sampling of submicrometer-sized airborne viruses is necessary, especially because of the high probability of their staying airborne and their deposition in the lower respiratory tract. Here, we present a novel personal electrostatic particle concentrator (EPC) for gentle sampling of submicrometer airborne virus particles. Owing to the enhanced electric field designed in this EPC, the collection efficiencies reached values as high as 99.3−99.8% for 0.05−2 μm diameter polystyrene particles at a flow rate of 1.2 L/min. Submicrometer-sized MS2 and T3 virus particles were also collected in the EPC, and the concentrations relative to their respective initial suspensions were more than 10 times higher than those in the SKC BioSampler. Moreover, the recovery rate of T3 was 982 times higher in the EPC (−2 kV) than in the BioSampler at 12.5 L/min because of the gentle sampling of the EPC. Gentle sampling is desirable because many bioaerosols suffer from significant viability losses during sampling. The influence of ozone generated, applied electrostatic field, and the flow rate on the viability of the viruses will also be discussed.

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recommended, and the sampling method and flow rate should be adjusted for a particular sampling purpose and target agent. For example, gentle sampling is required to reduce the viability loss induced during the process of collection of bioaerosols, especially if they are fragile and sensitive. Airborne virus particles can be generated from an infected host’s activities, such as breathing, sneezing, and coughing, and they can remain airborne for a long time if their aerodynamic sizes are small enough to neglect their gravitational settling. The sizes of naturally generated airborne virus particles can range from the size of the virus itself (20−300 nm) to the size of the particle aerosolized from the liquid suspension containing the viruses.2 There have been several studies about the size distribution of airborne viruses.4−7 However, no clear correlation has been shown between the size and the viability of a virus particle.4,5,7 Larger airborne virus particles may be more infective than smaller ones, because more viruses can be agglomerated into a single particle, and the larger volume of organic material surrounding the virus may better protect the virus from environmental stresses.8 However, larger virus particles may be less hazardous a long time after their

INTRODUCTION Airborne viruses that cause diseases such as swine influenza, avian influenza, and foot-and-mouth disease (FMD) are a cause of serious concern for both humans and animals because of their rapid infection through the respiratory system and spread via aerosol transmission. For example, the outbreak of the swine flu pandemic in 2009, caused by the influenza A (H1N1) virus, resulted in over 17 700 deaths as of March 2010, according to World Health Organization statistics.1 Therefore, it is critical to find information on the concentration and pathogenicity of the airborne viruses in order to take quick and effective steps to prevent further infection. However, there exist several technical issues associated with the concentration, recovery, and size distribution of the airborne viruses.2 The number concentration of airborne virus particles is usually very low, so high concentration of the particles from a large air volume into a small quantity of collection liquid through high flow rate sampling is required for effective detection. However, the mechanical impact in the case of high flow rate sampling can damage the virus particles, which can affect their biological recovery. Therefore, this may not be suitable for cultivation-based analysis, which is one of the most widely used quantification methods for bacteria and viruses.2 Moreover, superisokinetic sampling causes inlet particle losses,3 and high power consumption makes portability and installation difficult. Therefore, high flow rate sampling is not always © XXXX American Chemical Society

Received: July 9, 2016 Revised: October 7, 2016 Accepted: October 18, 2016

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DOI: 10.1021/acs.est.6b03464 Environ. Sci. Technol. XXXX, XXX, XXX−XXX

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MATERIALS AND METHODS Design of the EPC and Numerical Validation. The EPC was designed to gently and effectively collect various virus particles into a small volume of liquid medium. It was designed to be of a portable size and to have low power consumption. A simple needle type corona charger without sheath air was used for charging and for increasing the electrical mobility of the incoming aerosol particles. Although corona chargers are usually used to produce a high concentration of unipolar ions, the ozone generated during corona charging can inactivate the airborne viruses.31 Therefore, positive corona was chosen in this study, because it generates a much smaller amount of ozone than negative corona.32 This corona charger was composed of a grounded pipe, a needle pushed perpendicularly into the pipe, and a polymeric insulator between the pipe and the needle (Figure S1). The outlet of the charger and the inlet of the EPC were connected with an 8.9 mm inner diameter tube. From the standpoint of the electrostatic concentration of aerosol particles, the electrostatic forces exerted on the aerosol particles should be large enough, or the flow velocity over the collection electrode should be low enough, for the electrostatic attraction to overcome the drag force exerted on the charged particles so that the particles are directed to the electrode.33,34 Moreover, the size of the collection electrode should be small enough to obtain a high concentration of the airborne particles. A cylindrical body and a disk type collection electrode perpendicular to the central aerosol flow were chosen for this purpose (Figure 1); the geometry of this EPC is similar to that of DF-ESP.30 In both designs, the aerosol stream expanded immediately after entering the inlet, and the particle velocity reduced as the particle approached the collection electrode. However, to enhance the electric field strength over the collection electrode in the EPC, a part of this electrode was protruded from the bottom of the cylinder, and the side and

generation, as their concentration in the air decays faster than in the case of smaller virus particles.9 Therefore, submicrometer virus particles can be more harmful because of the high probability of their deposition in the lower respiratory tract.10 The infection of the lower respiratory tract is more dangerous, because the possibility of impairment of lung function can increase with severity, morbidity, and fatality.11 Therefore, sampling only micrometer-sized virus particles is not sufficient, and submicrometer virus particles should also be considered for the representative sampling of airborne viruses. Several types of air samplers have been developed for collection of micrometer-sized bioaerosol particles.2 Impactors and impingers use the inertial impaction of these particles, which is more effective for larger particles or higher flow rates. Hogan et al.12 evaluated several liquid impingers such as the all glass impinger AGI-30, the SKC BioSampler, and a frit bubbler, and they showed collection efficiencies of less than 10% for 30−100 nm virus particles. Recently, water condensation-based impingers were used to increase the size of incoming ultrafine viral particles and hence their collection efficiencies.13,14 Fibrous filters can also be used to sample ultrafine virus particles. However, extraction of the viruses from the filters is necessary in this case, and the structural damage and desiccation of the viruses during the sampling can decrease their viability and complicate the analysis.2 Gelatin filters can be completely melted in water and have higher biological recovery than the fibrous filters, and they recovered 8−13% of infectious influenza viruses compared with the BioSampler.15 Electrostatic precipitators (ESPs) have been increasingly studied for the collection of bioaerosols,16−28 as a wide range of airborne particles of different sizes can be collected using corona charging and subsequent electrostatic attraction. ESPs have exhibited collection efficiencies as high as 99% along with lower collisional stress and lower pressure drop.18 The airborne particles can also be concentrated using a small collection electrode.23,24 Many electrostatic samplers have been assessed for bacterial aerosols.18,23,24,26 Airborne virus particles have also been evaluated using ESPs; however, in these studies, either the mass mean particle diameter was a few micrometers,27 or the size distributions of the airborne viruses were not characterized.16,20,25 In this study, we developed a new personal electrostatic particle concentrator (EPC) to collect a high concentration of submicrometer-sized airborne virus particles into a small volume of liquid medium with a high recovery rate. We had previously proposed the structure of this EPC numerically using CFD-ACE,29 and in the current study, the experimental data under various conditions are presented by comparing with two well-known air samplers. The collection efficiencies for particles having sizes ranging from 0.05 to 2 μm were numerically and experimentally obtained and compared with the results for Dixkens and Fissan’s ESP (DF-ESP),30 the design of which was used in a commercial nanometer aerosol sampler (model 3089, TSI, MN). The physical and biological capture for MS2 and T3 bacteriophage particles were evaluated by using quantitative polymerase chain reaction (qPCR) and plaque assay, respectively, and they were compared with the measurements obtained with the BioSampler. The influence of ozone generated from the corona discharge, applied electrostatic field, and the flow rate of the samplers on the viability of the viruses will also be discussed in this paper.

Figure 1. Schematic of the EPC developed in this study. B

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Figure 2. Schematic of experimental setup including aerosol generation, collection, and measurement.

virus, and FMD virus.2 T3 phages, which have double-strand DNA genomes, are composed of an icosahedral capsid head with an inner diameter of 47 nm and a tail, which is 15 nm long and 10 nm in diameter.35 The tail is bonded to the capsid noncovalently, and this relatively weak bonding could be broken by mechanical stresses.36 Therefore, T3 phages were selected to examine the recovery of a fragile virus in the EPC and the BioSampler. Preparation of Viral Suspension. The viral suspensions for nebulization were prepared as follows. The host bacteria for MS2 and T3 were Escherichia coli C3000 (ATCC 15597) and Escherichia coli B (ATCC 11303), respectively. Each of these bacteria was inoculated in 10 mL of tryptic soy broth (TSB) (211825, Becton, Dickinson and Company, NJ) and incubated at 160 rpm and 37 °C for 12−13 h. Freeze-dried MS2 and T3 phages were dissolved in 1 × phosphate-buffered saline (PBS) (pH 7.4, GIBCO) with a concentration of 1 mg mL−1. For the propagation of the phages, 0.5 mL of the dissolved MS2 and T3 solutions were added to 10 mL of the E. coli C3000 and the E. coli B culture, respectively. The mixtures were further incubated at 160 rpm and 37 °C for 4−5 h, and the lysis of the host bacterial cells was then visible. The mixtures were centrifuged at 3000 rpm for 10 min to remove the bacterial cells and their debris, and the supernatants were filtered three times through low-protein-binding membrane filters with a pore size of 0.22 μm (4612, Pall Corporation, MI). The resulting viral stocks were stored at −20 °C. Upon use, the suspension for nebulization was made by adding 1.5 mL of the stock to 28.5 mL of deionized water. The viable virus concentrations of the suspensions were measured as 5.8 (±4.7) × 109 PFU mL−1 for MS2 and 7.1 (±4.2) × 108 PFU mL−1 for T3. Experimental Procedure. Two experiments were performed in this study; the schematic of the experimental setup is shown in Figure 2. First, monodisperse polystyrene particles (Fluoro-Max, Thermo Scientific, MA) were used to determine the optimal operating conditions for the EPC and to compare

top walls and the bottom of the cylinder were biased as the electrical ground; this arrangement is different from DF-ESP. Therefore, two outlets were located next to the inlet, whereas in DF-ESP, the bottom side was used for the outlet with an extended length for pumping. The electric field and flow field in the EPC and DF-ESP were calculated using COMSOL Multiphysics simulation software (Version 4.3) at an applied voltage of 25 kV and a flow rate of 0.3 L/min (lpm), which was the conditions used in Dixkens and Fissan’s experiment (Figure S2).30 The diameters of the collection electrodes in the EPC and DF-ESP were 20 mm, which allowed many analytical sample plates for scanning electron microscopy and biosensors to be placed on it. The collection electrode of the EPC was surrounded by a polymeric insulator, and a small amount of liquid medium can be placed on the collection electrode for further analysis. COMSOL was also used to simulate the particle tracks in the EPC and DF-ESP, and to compare the collection efficiencies for particles with different sizes. The simulated collection efficiencies of the EPC were compared with those of DF-ESP for the same flow rates at the inlets, areas of the collection electrodes, and distances between the inlets and the collection electrodes. The calculated collection efficiencies were based on the number of particles stuck to the surface of the sample plate (diameter: 30 mm) and the collection electrode (diameter: 20 mm) for DF-ESP and the EPC, respectively. Despite the smaller collection area in the EPC, the collection efficiencies of the developed EPC were higher than those of DF-ESP for particle sizes ranging from 0.3 to 1 μm, which is because of the enhanced electric field strength in the EPC (Figure S3). Test Virus. Bacteriophages MS2 (ATCC 15597-B1) and T3 (ATCC 11303-B3) were used as surrogates for the airborne viruses. MS2 phages are single-strand RNA viruses with 27 nm icosahedral capsid with no tail. MS2 has been widely used as a surrogate airborne virus because its morphology is similar to that of many pathogenic viruses including rhinovirus, polioC

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The number of charges produced by the corona charger can be indirectly calculated by measuring the discharging current. Evaluation of Virus Sampling. Quantitative PCR and plaque assay were used to measure genomic RNA/DNA concentration and PFU from the viral samples, respectively. The RNA/DNA concentration and PFU of the collected samples relative to those of the initial suspensions are shown as relative total virus concentration (RTVC) and relative infectious virus concentration (RIVC) respectively:

its collection efficiencies with those of the fabricated DF-ESP. Second, MS2 and T3 phages were used to examine the number of total and viable viruses collected in the EPC and the BioSampler. In the first experiment, polystyrene particles (diameters: 0.05, 0.1, 0.3, 0.38, 1, and 2 μm) in deionized water (concentration: 0.05 wt %) were nebulized using a three-jet Collison nebulizer (Mesa Laboratories, Denver, CO) with 3.0 lpm (at about 7 psi) of clean air. The clean air was supplied by filtering and drying compressed air using a clean air supply (Dekati, Finland), and by controlling the flow rate using mass flow controllers (model 5850E, Brooks Instrument, PA). The particles generated from the nebulizer were dried in a diffusion dryer (HCT, South Korea) and charge-neutralized in a diffusion neutralizer (model 5.622, GRIMM, Germany) equipped with an Am-241 radioactive source. Clean air was added to obtain diluted aerosols at 13.0 lpm. The number concentrations of the airborne particles 0.05−0.1 μm and 0.3−2 μm in diameter were measured using a scanning mobility particle sizer (measurement range: 0.01−1 μm, model 5.416, GRIMM, Germany) and an optical particle sizer (measurement range: 0.25−32 μm, model 1.109, GRIMM, Germany), respectively. An applied voltage of −10 kV with a corona voltage of 3.0 kV was used for the collection of test aerosols in the EPC and DF-ESP at flow rates of 1.2, 2.0, 6.0, and 12.5 lpm. The conditions used in the simulation were not adopted in the experiments, as a flow rate of 0.3 lpm is too low for the present sampling purpose, and an applied voltage of 25 kV is very high considering the dielectric breakdown of humid air. The collection efficiency was calculated based on the particle concentrations measured at the inlets and the outlets of the collecting devices: collection efficiency(%) =

Nupstream − Ndownstream Nupstream

RTVC =

qPCR collected qPCR initial

and RIVC =

PFUcollected PFUinitial

where qPCR collected and qPCRinitial are the RNA/DNA concentrations of the collected sample and initial suspension respectively, and PFUcollected and PFUinitial are the PFUs of the collected sample and initial suspension, respectively. In addition, the recovery rate of the virus was calculated by dividing RIVC by RTVC: recovery rate(%) =

RIVC × 100% RTVC

The recovery rate, therefore, indicates how much the ratio of the number of viable viruses to the number of total viruses in the initial suspension remains unchanged through the sampling process. The early log-phase cultures and TSB medium with 1.5% agar were used for the plaque assay of the phages based on the single layer method shown in the product information sheet (ATCC 15597-B1 and ATCC 11303-B3). The procedure of qPCR assay is shown in the Supporting Information. It includes the RNA isolation from MS2, complementary DNA synthesis from the RNA, design of the primers, construction of plasmid standards, and the qPCR amplification and analysis. Statistical Analysis. Each experiment in this study was performed at least thrice. The averaged values are shown in the figures, and their standard deviations are indicated as error bars. The Student’s t-test was used to determine whether the two selected cases were significantly different from each other or not. A p-value less than 0.05 was considered to be statistically significant.

× 100%

where Nupstream is the number concentration measured at the inlet of the sampler, and Ndownstream is the number concentration measured at the outlet of the sampler under a particular experimental condition. In the second experiment, the prepared suspensions of MS2 and T3 were nebulized with 3.0 lpm of clean air. After passing through the dryer and the neutralizer, the aerosols were diluted with 10 lpm of clean air. The size distribution of the aerosols was measured using the scanning mobility particle sizer. After placing 0.5 mL of the collection medium (1 × PBS) on the electrode of the EPC, the virus particles were collected at 1.2 lpm at various voltage conditions with the corona charging (3.0 kV). The BioSampler was operated at 12.5 lpm to collect the virus particles into 20 mL of the collection medium (1 × PBS). In order to investigate the influence of sampling velocity on the recovery of T3 phages, the EPC was operated at an applied voltage of −2.0 kV and flow rates of 1.2, 6.0, and 12.5 lpm while the BioSampler was operated at flow rates of 6.0, 10.0, and 12.5 lpm. After operating the two collecting devices for 10 min, these collection media were stored at 4 °C until they were taken for further analysis. The collection electrode of the EPC and the inside of the BioSampler were cleaned after each run. As the ozone produced from the corona charger can inactivate the viruses, the ozone concentration at the outlet of the EPC was measured by an ozone analyzer (model 49i, Thermo Scientific, MA). In addition, the discharging current was measured by an electrometer (Charme, PALAS, Germany).

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RESULTS AND DISCUSSION Physical Collection Efficiency. Figure 3 shows the collection efficiencies of the monodisperse polystyrene particles for the EPC and DF-ESP, and polydisperse MS2 particles for the BioSampler. The collection efficiencies at 1.2 lpm were 99.3−99.8% in the EPC and 95.9−99.4% in DF-ESP for the tested particle sizes, and they decreased as the flow rate was increased. The collection efficiencies reached the minimum values at a particle size of 0.3 μm, which can be attributed to the lowest electrical mobility around this particle size.34 The collection efficiencies for the all particle size and the flow rates were higher in the EPC than in DF-ESP. The higher collection efficiency is due to the enhanced electric field intensity in the EPC. Compared with the BioSampler at the same flow rate of 12.5 lpm, the collection efficiencies were higher in the EPC for fine particles smaller than 0.1 μm, but were lower for particles larger than 0.3 μm. It should be noted that this collection efficiency was based on the particle concentrations measured at the inlets and outlets of the collecting devices, which is a convenient and commonly used way to measure the collection efficiency. However, this collection efficiency does not reflect the actual number of particles captured on the collection spot D

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Figure 3. Collection efficiencies of the EPC and DF-ESP for charged polystyrene beads (diameters: 0.05−2 μm) at an applied voltage of −10 kV and flow rates of 1.2−12.5 lpm. The collection efficiencies were based on the number concentrations measured at the inlets and the outlets of three samplers: DF-ESP, the EPC, and the BioSampler. The collection efficiencies of the BioSampler at a flow rate of 12.5 lpm were adapted from the MS2 data reported by Hogan et al.12

for many samplers. For example, many particles were deposited on the inner surfaces of the charger and the EPC, with the former being dominant. The BioSampler also has similar losses, and the averaged internal particle losses were reported to be 29.6% for 0.9 and 3.2 μm polystyrene beads, B. subtilis cells, and C. cladosporioides spores.37 That is, approximately 30% of the particles present in the collection fluid remained attached to the inner surface of the BioSampler without leaving it. Collection of Virus Particles (EPC vs BioSampler). Most of the aerosolized MS2 and T3 particles were submicrometersized, and the particle size distribution agreed well with the lognormal distribution with the peak around 36 nm (Figure S4). The particle size distribution measured after the nebulization and subsequent drying was mainly affected by the suspension media, irrespective of the virus size and its presence in the suspension. The same behavior was also observed in the work published by Hogan et al.12 The RTVC was measured from the MS2 and T3 viruses collected in the EPC and the BioSampler (Figure 4). The RTVC increased as the magnitude of applied voltage in the EPC was increased, for both MS2 and T3, because the higher number of particles can be collected with higher electric field strength. The RTVC was 10.4 and 10.6 times higher in the EPC (at −10 kV) for MS2 and T3 particles, respectively, than in the BioSampler although a flow rate of 1.2 lpm was used in the EPC compared with 12.5 lpm used in the case of the BioSampler. This high virus capture in the EPC can be attributed to the enhanced electric field strength and the higher collection efficiencies for submicrometer particles in the EPC, as shown in Figure 3. The RIVC increased as the magnitude of applied voltage in the EPC was increased (Figure 5). For MS2 phages, the RIVC was 7.2 times higher in the EPC (at −10 kV) than in the BioSampler. There were also significant differences in the RIVC

Figure 4. Relative total virus concentration of the MS2 (A) and T3 (B) viral particles collected in the EPC and the BioSampler. The total virus concentration was obtained using qPCR.

between the EPC and the BioSampler regarding T3 phages. The RIVC for T3 in the EPC at the applied voltage of −2 kV was 1682 times higher than that in the BioSampler. Interestingly, when the magnitude of the applied voltage was increased from 2 kV to 10 kV, the RIVC and recovery rate in the EPC for the charged T3 particles decreased significantly (p = 0.047 and 0.001, respectively) (Figure 5B and 5C). Ozone and other reactive species are generated during corona discharging, which usually inactivates the viruses.21 However, the concentration of the generated ozone was approximately 4 ppb with corresponding ozone dose less than 0.1 min-ppb under the test conditions (Figure S6). This ozone concentration was too low to inactivate the phages, considering that 90% inactivation of MS2 and T7 requires an ozone dose of 652 and 1009 min-ppb, respectively, at 55% RH.31 The T7 phage, which is similar to the T3 phage in structure, was more resistant to ozone than the MS2 phage; thus ozone inactivation may not be an explanation for the decreased PFU level for T3. Therefore, it is more likely that the T3 phages were damaged when they were exposed to the high electric field intensity.21 Since both the head and tail of T3 can be charged with the same polarity and hence can form strong repulsive force,36 they might be more easily separated under the high electric field. MS2 viruses do not have the head and tail structure, and their RIVC and recovery rate did not decrease significantly as the magnitude of the electric field was increased from 2 kV to 10 kV (p = 0.449 and 0.387, respectively). Moreover, their E

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collected with the BioSampler for 10 min. To further investigate the influence of the sampling velocity or mechanical impact on the recovery of T3 phage in the EPC and the BioSampler, different sampling flow rates were used to collect the viral aerosols (Figure 6). The recovery rate of T3

Figure 6. Recovery rate and RTVC of the collected T3 phages in the EPC and the BioSampler with different sampling flow rates. Applied voltage of −2 kV was used in the EPC with the corona charging.

dramatically decreased with the increase in flow rates from 6.0 lpm to 12.5 lpm in the BioSampler. In fact, the average velocity at the three 0.6 mm diameter nozzles of the BioSampler changed from 118 m/sec to 313 m/sec as the flow rate increased from 6.0 lpm to 12.5 lpm.38 On the contrary, the average velocity at the inlet of the EPC increased from 1.6 m/sec to 3.3 m/sec and the recovery rate of T3 did not decrease significantly in the EPC (p = 0.202), as the flow rate was increased from 6.0 lpm to 12.5 lpm. The BioSampler requires a short distance of approximately 10 mm from the nozzle exit to the inner surface of the vessel, so that the aerosol jet does not spread and reduce the velocity significantly.39 On the contrary, the distance between the inlet and the collection plate of the EPC was as long as 150 mm to reduce the aerosol velocity. The recovery rate in the EPC was not only 982 times higher than that in the BioSampler but the RTVC was also almost the same as the BioSampler at a flow rate of 12.5 lpm. The high recovery rate and high physical collection can make this EPC a promising candidate for gentle sampling of fragile viruses. In fact, many bioaerosols suffer from significant viability losses during the sampling process, making it very difficult to estimate their actual viable concentrations in air.40 In summary, a novel personal EPC was developed for gentle sampling of submicrometer airborne virus particles. Owing to the enhanced electric field strength designed in this EPC, the collection efficiency reached 99.3−99.8% for 0.05−2 μm diameter polystyrene particles at a flow rate of 1.2 lpm. The number of total and infectious MS2 and T3 phages collected relative to their respective initial suspensions was much larger in the EPC than in the BioSampler. Gentle sampling of this EPC was even suitable for the effective biological sampling of sensitive and fragile viruses as it reduces the viability loss induced during the collection process of bioaerosols. However, as this EPC can operate for only a few hours because of the evaporation of the collection media, automatic media supply

Figure 5. Relative infectious virus concentration of the MS2 (A) and T3 (B) particles collected in the EPC and the BioSampler, and their recovery rates (C) in the EPC (1.2 lpm) and the BioSampler (12.5 lpm). The infectious virus concentration was obtained using plaque assay.

recovery rates at applied voltages of −2 kV, −5 kV, and −10 kV were not significantly different from that of the BioSampler (p > 0.072). There was a considerable decrease in the viability of T3 in the BioSampler, which may be because the T3 phages were damaged due to the high sampling velocity in the BioSampler. Hogan et al.12 also showed a low RIVC of approximately 3.4 × 10−5 when submicrometer and ultrafine T3 particles were F

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would be needed. This EPC can be further used for direct concentration of airborne viruses onto the sensing area of a biosensor for rapid monitoring.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.6b03464. Figures showing schematics of the corona charger; calculated equipotential lines and velocity field in the EPC and DF-ESP; numerical collection efficiencies in the EPC and DF-ESP; procedure of qPCR assay; measured size distributions of nebulized MS2 and T3 suspensions; collection efficiencies in the EPC with and without the collection medium; ozone concentration and discharging current from the corona charger (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Phone: +82-52-217-2323; fax: +82-52-217-2309; e-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the staff of the UNIST Design & Manufacturing Center (UCRF) for fabrication support. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (#2015R1A2A2A01006446), and the 2016 Research Fund (1.160005.01) of UNIST.

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DOI: 10.1021/acs.est.6b03464 Environ. Sci. Technol. XXXX, XXX, XXX−XXX