Filtration performances of HVAC filters for PM10 and microbial aerosols— Influence of management in a lab-scale air handling unit

Filtration performances of air handling unit (AHU) filters for particles and microbial aerosols were investigated. The influence of the AHU operational conditions on the behavior of microorganisms collected on the filters was also studied. A lab-scale AHU with two filtration stages was developed and validated for the study of downsized filters with industrial geometries. Three types of filters of different efficiency were considered: G4, F7, and F9, according to European standard EN 779. Two configurations of filters were studied: G4 pleated/F7 bag and F7/F9 bag. Filters were sequentially clogged by alumina particles, which provided a mineral fraction in the particulate cake, and then by micronized rice particles, which provided the fungus Penicillium chrysogenum and an organic fraction that acts as a substrate for microorganisms. Finally, a microbial aerosol composed of endospores of Bacillus subtilis and spores of Aspergillus niger was nebulized to contaminate filters. After clogging, periods of 5 days on and 2 day weekend stops with restarts of ventilation were simulated for 6 weeks. The results showed that the filter efficiency for particles was quite comparable to that for microbial aerosols expressed in cultivable concentration. The particulate cake composed of alumina and micronized rice particles enabled the growth of the endogenous species P. chrysogenum and the survival of exogenous species B. subtilis and A. niger on filters. During restarts of ventilation, low particle concentrations were detected downstream of the second filtration stages by release but the microbial concentration from the fraction of air sampled was below the detection limit.

© 2016 American Association for Aerosol Research     

Profile and Morphology of Fungal Aerosols Characterized by Field Emission Scanning Electron Microscopy (FESEM)

Fungal aerosols consist of spores and fragments with diverse array of morphologies; however, the size, shape, and origin of the constituents require further characterization. In this study, we characterize the profile of aerosols generated from Aspergillus fumigatus, A. versicolor, and Penicillium chrysogenum grown for 8 weeks on gypsum boards. Fungal particles were aerosolized at 12 and 20 L min^?1 using the Fungal Spore Source Strength Tester (FSSST) and the Stami particle generator (SPG). Collected particles were analyzed with field emission scanning electron microscopy (FESEM). We observed spore particle fraction consisting of single spores and spore aggregates in four size categories, and a fragment fraction that contained submicronic fragments and three size categories of larger fragments. Single spores dominated the aerosols from A. fumigatus (median: 53%), while the submicronic fragment fraction was the highest in the aerosols collected from A. versicolor (median: 34%) and P. chrysogenum (median: 31%). Morphological characteristics showed near spherical particles that were only single spores, oblong particles that comprise some spore aggregates and fragments (<3.5 μm), and fiber-like particles that regroup chained spore aggregates and fragments (>3.5 μm). Further, the near spherical particles dominated the aerosols from A. fumigatus (median: 53%), while oblong particles were dominant in the aerosols from A. versicolor (68%) and P. chrysogenum (55%). Fiber-like particles represented 21% and 24% of the aerosols from A. versicolor and P. chrysogenum, respectively. This study shows that fungal particles of various size, shape, and origin are aerosolized, and supports the need to include a broader range of particle types in fungal exposure assessment.     

Differences in Detected Fluorescence Among Several Bacterial Species Measured with a Direct-Reading Particle Sizer and Fluorescence Detector

Naturally-contained fluorescing chemicals (such as riboflavin or NADPH) can be used to detect the presence of biological organisms. A new instrument from TSI Incorporated measures fluorescence of particles using an ultraviolet laser operating at an excitation wavelength of 355 nm. We have employed this instrument (Model 3312 Ultraviolet Aerodynamic Particle Sizer (tm) Spectrometer) to assess the degree of fluoresence associated with a variety of biological aerosols. Nonfluorescent and fluorescent latex sphere and sodium chloride aerosols were first used to assure proper operation of the instrument and to obtain correct instrument settings. Biological aerosols were then generated by combining organisms with double distilled and filtered water in a Collison nebulizer operated at low pressure. After passage through a charge neutralizer and dilution with humidified air (45%RH), the aerosol was measured downstream for both particle size and fluorescence distributions. Bacterial aerosols generated include Bacillus subtilis subsp. niger (spores and vegetative cells), Staphylococcus epidermidis, Eschericia coli, and Mycobacterium abscessus (a surrogate for M. tuberculosis). Cladosporium spp. fungal spores were also evaluated, and the effect of heat treatment on fluorescence was tested using B. subtilis spores. For each test the percentage of organisms that produced a fluorescence signal above a threshold was recorded. The organisms demonstrated considerable differences in percent fluorescence, ranging from means of 11% for S. epidermidis to 44% for B. subtilis spores. Vegetative cells of B. subtilis were generally less fluorescent (mean of 33%) than the spores, while the highest level of fluorescence was associated with heat-treated spores (averaging about 75%). This instrument has some potential for use in settings where immediate detection of biological organisms is important. Work remains to be done on understanding the effect on fluorescence of organism viability, presence of nonbiological particles, and interferences from mixtures.     

Identification of single microbial particles using electro-dynamic balance assisted laser-induced breakdown and fluorescence spectroscopy

Online characterization of fungal and bacterial spores is important in various applications due to their health and climatic relevance. The aim of this study was to demonstrate the capability of the combination of electro-dynamic balance assisted laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) techniques for the online detection of single fungal spores (Aspergillus versicolor and Penicillium brevicompactum) and bacteria (Bacillus aureus). The method enabled sensitive and repeatable LIBS analysis of common elemental components (Ca, Na, and K) from single microbial particles for the first time. Significant differences in the concentrations of these elements were observed between the species, e.g., bacterial spores had over three orders of magnitude higher Ca concentration (2 × 10^?12 g/particle) compared to fungal spores (3–5 × 10^?16 g/particle). The LIF analysis has previously been used to distinguish bioaerosols from other aerosols due to their fluorescence ability. This study showed that combination of LIF and LIBS analysis is a promising tool for identification of different bioaerosol particle types.

Copyright © 2016 American Association for Aerosol Research     

Treatment of Air Filters Using the Antimicrobial Natural Products Propolis and Grapefruit Seed Extract for Deactivation of Bioaerosols

Two natural products; i.e., grapefruit seed extract (GSE) and propolis, were investigated for use in antimicrobial air filters. Staphylococcus aureus was investigated as a test bioaerosol, and was deposited on the antimicrobial filters, which were treated by spraying with various areal densities of GSE and propolis. The pressure drop and particle penetration were investigated to assess the filtration performance of the bioaerosol, and the bacterial-inactivation performance of the filters was evaluated by quantifying S. aureus. There was little change in the pressure drop as a function of the areal density of GSE up to 185.9 μg/cm²; however, a significant change in the pressure drop was found for the air filter coated with propolis at an areal density of 98.4 μg/cm². The penetration levels of bioaerosols in both filters were uniform and in the range 1.4–2.0% (based on particle number), regardless of the areal density of the deposited GSE or propolis. The inactivation rates of the filters with identical deposition masses of GSE and propolis were similar in the ranges of 92.1–100%, 75.2–89.1%, and 54.4–75.5% at the control filters with colony numbers of 10³, 10⁴, and 10⁵ CFU/mL, respectively. The bacterial inactivation rate could be described by an exponential function of the areal density of GSE/propolis per number of colonies.

Copyright 2015 American Association for Aerosol Research     

Aerosol-to-Hydrosol Transfer Stages for Use in Bioaerosol Sampling

Single-jet and multijet aerosol-to-hydrosol transfer stages (AHTSs) with cutpoints of 2 and 0.8 μm aerodynamic diameter, respectively, were designed and evaluated. The devices are intended to take the coarse particle flow stream (minor flow) from a virtual impactor and concentrate the aerosol particles into a low flow rate of liquid. The design air flow rate for each system is 1 L/min, and the collection liquid flow needs to be ≥ 0.3 mL/min with a surfactant added to prevent loss of hydrosol particles on internal surfaces of the devices. Satisfactory performance was achieved when distilled water with 0.1% Tween 20 was used as the collection fluid. The effectiveness (average fractional efficiency) for the single-jet device is 94% over the size range of 2.5 to 10 μ m aerodynamic diameter, and that of the multijet AHTSs is 90% over the size range of 1 to 10 μ m aerodynamic diameter. The systems have an ideal air power consumption of 1.4 mW and 4.5 mW, respectively. If an AHTS were operated in a heated enclosure and sampled air at ?28°C, less than 1 W of heating would be required to prevent freezing. Preliminary results of bioaerosol testing with 0.7 μm AD single spores of Bacillus globigii var. niger show efficiencies over 100%. These values are probably due to the different expression of viability of the spores in the reference samples and those in the output liquid of the AHTSs.     

Association Between Increased DNA Mutational Frequency and Thermal Inactivation of Aerosolized Bacillus Spores Exposed to Dry Heat

Inactivation of viable bioaerosol particles, especially stress-resistant microorganisms, has important implications for biodefense and air quality control. It has earlier been shown that the loss of viability of bacterial endospores due to exposure to dry heat is associated with mutational damage. Previous studies, however, used non-aerosolized spores, long exposure times, and moderately elevated temperatures. This study was designed to investigate the mechanism of inactivation of aerosolized Bacillus endospores exposed to high temperatures for sub-second time periods. Bioaerosol was tested in a continuous air flow chamber under two flow rates, 18 L/min and 36 L/min. The chamber had a cylindrical electric heating element installed along its axis. The estimated characteristic exposure temperature (T_exposure ) ranged from 164°C to 277°C (with an uncertainty of 21–26°C). To quantify mutational frequency, spores were cultivated after dry heat exposure on tryptic-soy agar and on antibiotic nalidixic acid media. Increases in the exposure temperature caused viability loss and increase in mutational frequency of the spore DNA. Significant association was found between the inactivation factor and the mutational frequency ratio (heat exposed versus non-exposed) with R² of 0.985 for both flow rates combined. The results suggest that mutational damage is involved in the causal chain of events leading to inactivation of aerosolized endospores exposed to heat for sub-second time periods.     

Use of an Andersen Bioaerosol Sampler to Simultaneously Provide Culturable Particle and Culturable Organism Size Distributions

A method is provided for estimating size distributions in terms of both culturable particles (CP) and culturable organisms (CO) from a single sample collected with an Andersen bioaerosol impactor. Half of the agar surface of each Petri dish is covered with a polycarbonate filter substrate through which liquid from the agar can wick and thereby form a flat wetted collection surface, and the other half of the agar surface is uncovered. Quantification of CO distribution results involves washing the collected particles from the filter surfaces and plating suitable dilutions of de-agglomerated particles, followed by incubating the organisms, and counting the resulting colonies; whereas, quantification of CP results is based on direct culturing of the agar media. Experiments were conducted with near-monodisperse clusters of Bacillus atrophaeus (aka BG) aerosols covering APS-determined geometric number mean sizes from 1.83 to 8.7 μm aerodynamic diameter (AD). There is little difference between the Andersen-determined median sizes of the CO and CP distributions of the near-monodisperse clusters, which supports the utility of the CO method. The method was applied to sampling bioaerosol in a previously occupied classroom and the results showed median sizes of 1.7 and 3.1 μm AD for the CP and CO distributions, respectively. Total bioaerosol concentrations were 0.53 and 3.4 CO/L, respectively, so the average CP contained 6.4 CO.

Copyright 2012 American Association for Aerosol Research     

Bench-Scale Aerosol Filtration Test System and Evaluation of an Acoustic Bioaerosol Removal Device for Indoor Air Streams

It is important to have well-defined, reproducible methods to evaluate and compare newly developed air filtration equipment. To facilitate accurate assessment of air purification devices at the bench scale, an experimental system was designed, built, and documented to evaluate particulate removal efficiency (PRE) of air filtration devices based on principles used in ASHRAE standards. The system was then carefully characterized and used to evaluate PRE and total energy consumption of a novel acoustically enhanced impaction (AEI) air purification device. The AEI device demonstrated 99.998% PRE of 0.5–1.5 μm diameter KCl particles while causing a 120 Pa pressure drop and requiring a total of 3.0 W/l of air treated at indoor ambient conditions. A single element of the AEI device operated in a biological safety level 2 facility was then used to evaluate PRE of bioaerosol consisting of Bacillus cereus (BC) spores. PRE of BC was 99.86 ± 0.05% at indoor ambient temperature and pressure. This research describes the use of the Bench-scale Air Purification Testing and Evaluation Chamber (BAP-TEC) to experimentally evaluate and compare PRE and total energy requirements of novel air purification devices at the bench scale (280–1400 alpm). Further, an AEI device containing a fibrous filter media and high intensity sound field in the same control volume is evaluated using the BAP-TEC. Temporally resolved PRE of a bioaerosol by the AEI is also presented.

Copyright 2013 American Association for Aerosol Research     

Effects of single-walled carbon nanotube filter on culturability and diversity of environmental bioaerosols

In this study, single-walled carbon nanotube (SWNT) filters were prepared using mixed cellulose ester (MCE) filters and carbon nanotubes with three levels of loading: 0.02, 0.16 and 0.64 mg/cm². Both MCE and SWNT filters were used to collect bacterial and fungal aerosols with a total volume of 200 L air sampled in indoor and outdoor environments. After sampling, the filters were directly placed on agar plates at 26 °C for culturing. The culturable aerosol counts were manually obtained both for MCE and SWNT filters, and the resulting bacterial colony forming units (CFUs) were washed off and subjected to the culturable bioaerosol diversity analysis using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). For fungal CFUs, microscopy method was used to study the diversity obtained using different filter types.The results showed that use of SWNT filters with medium and high CNT loadings resulted in significant reduction (up to 2 logs) of culturable bacterial and fungal aerosol counts compared to MCE filters in both environments. For low CNT loading (0.02 mg/cm²), very limited inactivation effects were observed for fungal aerosols, while more bacterial counts were obtained possibly due to increased sampling efficiency. PCR-DGGE analysis revealed that SWNT filters at high CNT loading (0.64 mg/cm²) resulted in lowest culturable bioaerosol diversity, especially pronounced for outdoor bacterial aerosols. For low and medium CNT loading, the culturable bacterial aerosol diversity remained similar. Fungal aerosol analysis showed that the use of SWNT filters with medium to high CNT loading also resulted in significant reduction of fungal species diversity. The results here demonstrated great promise of the SWNT hybrid filter in controlling biological aerosols, and suggested its potential to impact current air conditioning system.     

Aluminum-based materials for inactivation of aerosolized spores of Bacillus anthracis surrogates

Energetic materials generating biocidal combustion products to disable airborne pathogenic microorganisms (including bio-threat agents) were designed as compounds of halogens and metals with high heats of oxidation. Thermally stable Al-based powders containing iodine and chlorine were prepared using ball-milling at room and cryogenic temperatures. Such powders can replace pure aluminum in metallized energetic formulations. Their stability and halogen release were quantified using thermo-gravimetric analysis. Ignition temperatures were determined by coating prepared powders onto an electrically heated filament. All prepared composites had lower ignition temperatures and longer combustion times compared to pure Al. In separate experiments, combustion products generated by injecting the prepared powders into an air-acetylene flame were mixed with a well-characterized bioaerosol. Inactivation of viable bioaerosol particles exposed to the heated combustion products for a short period of time (estimated to be 0.33 s) was quantified. The combustion products of materials investigated in this study effectively inactivated the aerosolized spores of two tested surrogates of Bacillus anthracis (B. atrophaeus and B. thuringiensis var kurstaki). A ternary composite with 20 wt% of iodine, 40 wt% of aluminum and 40 wt% of boron was found to be most attractive based on both its stability and efficiency in inactivating the aerosolized spores. The inactivation achieved was primarily attributed to chemical stresses as the thermal effect could not solely produce the high measured levels of inactivation. The findings point to a possible synergy of the thermal and chemical spore inactivation mechanisms.

© 2017 American Association for Aerosol Research     

Design and evaluation of a new device for fungal spore aerosolization for laboratory applications

Fungi have significant health effects varying from serious allergic reactions from inhalation to toxic effects and even fatal infections. Indoor and outdoor sampling may identify potentially contaminated environments, but sampling techniques need refining to set risk levels regarding occupational exposure or to assess and analyse sudden outbreaks of fungi. As little is known of the sporulation and dispersal dynamics of fungi, we have experimented with aerosolizing fungal spores from cultures grown in standard 9 cm Petri dishes for 3–10 h using a new device that incorporates vibration. We evaluated the effect of the air flow and frequency on a quantity and pattern of spores aerosolized. Frequency had positive, negative or no effect. Positive quantitative effects were noted in Aspergillus versicolor at 50 Hz, in Aspergillus niger at 400 Hz and at 100–400 Hz in Rhizopus. Aerosolization of Aspergillus species dropped significantly in the first 20 min and then stabilised for 2.5–3 h. After this time period, the generation process became highly unstable with large quantities of small particles produced. It could be explained by appearance of cracks on the nutrient surface due to desiccation with corresponding release of particles of nutrient to the air carrier. For Rhizopus, the initial steep decrease in particle generation for the first 20 min of the process was followed by quite stable spore production for the following 10 h of process operation. There were no cracks observed on the nutrient surface for the entire 10 h operation of the device. The air flow also affects the efficiency of the spore release. It was found that increase in the air flow was associated with more efficient sporulation from the nutrient dish. On the other hand, the size distribution curve of the airborne spores produced at higher air flows was correspondingly slightly shifted towards larger sizes, which is related to less efficient loosening of spores and corresponding increase in concentration of clumps consisting of more than one spore. Also, it was found that incubation of fungal cultures for extended periods (2–6 weeks) led towards production of larger numbers of airborne fungal spores.     

A Puff of Air Sorts Bioaerosols for Pathogen Identification

Optical-based, real-time bioaerosol sensors are able to distinguish bioaerosols and nonbioaerosols but are unable to classify pathogens or even discriminate harmful from harmless bacteria. Biochemical techniques can identify genus and species of bacteria but cannot do so efficiently due to time limitation and the very high concentration of background aerosols. We report for the first time an efficient aerosol sorter consisting of an aerodynamic deflector that is cued from bioaerosol fluorescence. Bacillus subtilis (anthrax stimulant) aerosol was successfully separated from mixed aerosols. We achieved enrichment of the suspected bioaerosol concentration by at least 10³, thus leading us new perspectives in pathogen identification. Although, at the present stage, a complete characterization of bioaerosols in real time is not yet possible, this new early warning/alarm sensor can supply high concentration of suspect bioaerosol particles for further specific analysis via bio-chemical assay technology or other subtle optical methods such as Raman spectroscopy.     

Design and Collection Efficiency of a New Electrostatic Precipitator for Bioaerosol Collection

We have developed and tested a new bioaerosol sampler in which airborne microorganisms are collected by electrostatic means. In this sampler, 2 ionizers charge the incoming particles if they carry insufficient electric charge for efficient collection. The organisms are then subjected to a precipitating electric field and are collected onto 2 square agar plates positioned along the flow axis. Tests with nonbiological NaCl particles versus B. subtilis var. niger (BG) spores and vegetative cells have shown that airborne microorganisms are collected more efficiently than nonbiological particles, even when the microorganisms have first passed through an electric charge neutralizer with no additional charging applied. The difference was attributed to the natural charges contained in cell membranes or spore coats of the microorganisms. Charge-neutralized BG spores and vegetative cells were collected at 4 L/min with efficiencies close to 80%, depending on the precipitation voltage, versus 50-60% for NaCl test particles. When incoming BG spores were charged with positive ions and then collected by a precipitating voltage of + 1,300 V, about 80% of the incoming spores were collected and more than 70% of incoming spores formed colonies. These experiments with BG spores have also indicated that there were no significant particle losses inside the sampler. The collection efficiency of biological and nonbiological particles increased to 90-100% when the particles were externally charged and the precipitating voltage was increased to more than - 4,000 V. It has also been shown that the aerosolized BG spores (used as anthrax simulants for bioaerosol sensors) carry a net negative electric charge. Thus the collection efficiency depends on the polarity of the electric field applied across the agar plates. These findings indicate that the collection of airborne microorganisms is possible by electrostatic precipitation without prior electric charging if the microorganisms already carry electric charges. These are usually high immediately after their release into the air.     

Antimicrobial Air Filtration Using Airborne Sophora Flavescens Natural-Product Nanoparticles

We investigated nanoparticle generation from a natural plant extract using the aerosol technique of the nebulization-thermal drying process, and tested its usefulness for antimicrobial air filtration. Sophora flavescens Ait. ethanolic extract was prepared as an antimicrobial natural-product suspension. Suspension droplets were generated using a single-jet Collison nebulizer, passed through an active carbon absorber to remove ethanol, and mixed and dried with sheath air. For drying, natural-product particles were exposed to 200°C for ～1 s. Finally, particles were introduced into a scanning mobility particle sizer, and their size distribution and morphology were analyzed. For application of natural-product particles to antimicrobial air filtration, the nanosized particles generated were deposited continuously onto air filter medium at various times. Physical characteristics (filtration efficiency, pressure drop, and fiber morphology by scanning electron microscopy), and biological characteristics (antimicrobial tests against Staphylococcus epidermidis, Bacillus subtilis, and Escherichia coli bioaerosols) were then evaluated. We also analyzed the chemical composition of particles deposited on the filter surface. The results showed that the nanoparticles generated were spherical and demonstrated a polydisperse size distribution, ranging from several tens to several hundred nanometers. Although the filter pressure drop increased with the amount of nanoparticle on the filter, the bioaerosol filtration efficiency and antimicrobial activity were enhanced. In particular, the S. flavescens natural-product nanoparticle-deposited filters were more effective for removal of Gram-positive than Gram-negative bioaerosols. These results are promising for the implementation of this new technology for control of air quality against hazardous bioaerosols.     

Aerosolization of Bacterial Spores with Pressurized Metered Dose Inhalers

Bioaerosol detection and identification systems need to be periodically checked for assurance that they are responsive to aerosol challenges. Herein, pressurized metered dose inhalers (pMDIs) containing ethanol suspensions of two simulants for B. anthracis spores are considered for providing suitable aerosols. Doses and shot weights from pMDIs with canisters having volumes equal to that of 200 metering-valve actuations were constant for ≤165 actuations, but drop beyond that range. There were statistically significant dose variations between replicate pMDIs and between two types of actuators used on the pMDIs. The storage half-lives of pMDIs filled with Bacillus atrophaeus (BG) and Bacillus thuringiensis subsp. israelensis (Bti) spore formulations are predicted to be 32 and 136 months, respectively, if the canisters are stored under refrigeration (4°C). The prediction is based on use of a logarithmic regression model relating CFU per actuation to storage time, with data taken at times of 1–12 months. Demonstration of the utility of the concept was provided by producing responses from a polymerase chain reaction (PCR) identifier with pMDI-generated BG and Bti aerosols that were collected with a 100 L/min wetted wall bioaerosol sampling cyclone.

Copyright 2013 American Association for Aerosol Research     

Model for Gas‐Liquid Flow through Wet Porous Medium

A method involving bubbling of air through a fibrous filter immersed in water has recently been investigated (Agranovski et al. [1]). Experimental results showed that the removal efficiency for ultra‐fine aerosols by such filters was greatly increased compared to dry filters. Nuclear Magnetic Resonance (NMR) imaging was used to examine the wet filter and to determine the nature of the gas flow inside the filter (Agranovski et al. [2]). It was found that tortuous preferential pathways (or flow tubes) develop within the filter through which the air flows and the distribution of air and water inside the porous medium has been investigated. The aim of this paper is to investigate the geometry of the pathways and to make estimates of the flow velocities and particle removal efficiency in such pathways. A mathematical model of the flow of air along the preferred pathways has been developed and verified experimentally. Even for the highest realistic gas velocity the flow field was essentially laminar (Re ≈ 250). We solved Laplace's equation for stream function to map trajectories of particles and gas molecules to investigate the possibility of their removal from the carrier.     

Development of a Personal Sampler for Collecting Fungal Spores

Exposure to fungal aerosols is of concern in indoor environments. However, sampling limitations have previously made it difficult to assess exposures accurately, especially long-term exposures. A prototype personal aerosol sampler, based on cyclone principles and using a 1.5 ml microcentrifuge tube as a particle collection receptacle has been designed and fabricated. Collection efficiency for aerosol particles in the size range of fungal spores has been evaluated for different types of microcentrifuge tubes, together with the effect of a polyethylene glycol coating on the inside of the tube and the effect of adding water to the tube. Monodisperse, fluorescently tagged polymer microspheres with median diameters of 0.5, 1, 2, 3, 6, 11, and 16 μm were used to evaluate sampler performance with particle diameter. The microcentrifuge-tube sampler was tested at flow rates of 2 and 4 liters per minute (l/min). Experimental results indicate that the microcentrifuge-tube sampler has an aspiration efficiency of 100% in calm air for particles up to 16 μm. At 4 l/min, the microcentrifuge-tube sampler is able to collect nearly 100% of particles greater than 3 μm and > 90% of particles between 2.5 and 3 μm. The 50% cutoff size is 1.5 μm. The performance of the sampler did not vary with the different brands of tubes tested or with the presence or absence of a coating on the tube surface. Furthermore, the addition of water to the tube resulted in a slight increase in collection efficiency. A sampling time of 5 h was feasible at 45–50% relative humidity before evaporation led to significant water loss.

The cutoff size of 1.5 μm is comparable to many commercially available bioaerosol samplers. Besides being easy to use, simple to fabricate, and inexpensive, this novel sampler has several advantages over conventional samplers: long-term samples are possible (the limitation of impaction methods); there is no sample transfer loss since the transfer step has been eliminated (the limitation of filter cassettes); laboratory analyses are not dependent solely upon a single analysis method (the limitation of impaction methods), and there is no sampler adherence loss (the limitation of trying to wash microorganisms from filters). In addition, use of the sampler would be applicable in a variety of occupational settings from low bioaerosol concentrations (i.e., indoor environments) to high bioaerosol concentrations (i.e., agricultural setting) by varying sampling time periods and using sensitive analytical methods.     

Factors Influencing Rapid Detection of Bioaerosols by Surface Plasmon Resonance-Based Technique

In bioaerosol monitoring applications, technologies allowing rapid and precise detection of airborne pathogens are highly demanded. One of such technologies, based on the immunoreaction-operating principle in nearly real-time mode without any specific labeling, is known as surface plasmon resonance (SPR). In previous studies, we have shown applicability of the SPR technology for rapid and selective detection of viral and bacterial aerosols where successful combination of the SPR machine with our earlier produced personal bioaerosol sampler opened new prospects in development of portable bioaerosol monitors. The current study is a logical continuation of our previous research dedicated to the technology development for rapid bioaerosol detection. Here, we focus on one of the main factors possibly influencing the SPR-based bioaerosol monitoring; the SPR performance on target bioaerosol detection was evaluated at conditions of substantial air contamination with different nontargeted microorganisms, commonly presented in the air. Besides, different compositions of sampling liquids were tested in regards to the SPR results interference. Our findings clearly verified high specificity of the technology even in cases of highly contaminated air environments with aerosols of biological and mineral origins. It was found that both nontargeted bioaerosols and nanosized aerosols of mineral background do not have significant influence on the specific SPR detection of targeted bioaerosols.

Copyright 2014 American Association for Aerosol Research     

Performance of Two Fluorescence-Based Real-Time Bioaerosol Detectors: BioScout vs. UVAPS

A 405 nm diode laser-based on-line bioaerosol detector, BioScout, was tested and compared with the Ultraviolet Aerodynamic Particle Sizer (UVAPS). Both instruments are based on laser-induced fluorescence of particles. Only a fraction of microbial particles produce enough fluorescence light to be detected by the instruments. This fluorescent particle fraction (FPF) is aerosol and instrument specific. The FPF values for common bacterial and fungal spores and biochemical particles were experimentally determined for both instruments. The BioScout exhibited higher FPF values for all the test aerosols except coenzyme NADH. The difference was higher for smaller particles. The FPF values of fungal spores and bacteria varied between 0.34 to 0.77 and 0.13 to 0.54 for the BioScout and the UVAPS, respectively. The results indicate that the 405 nm diode laser is a useful excitation source for fluorescence-based real-time detection of microbial aerosols. The FPF results of this study can be utilized to estimate the actual concentrations of bacterial and fungal spores in fluorescence-based ambient measurements.

Copyright 2014 American Association for Aerosol Research