Personal Bioaerosol Sampler Research Articles

In-situ rapid bioaerosol detection in the ambient air by miniature multiplex PCR utilizing technique

Given the current problems associated with the COVID-19 pandemic, research in the field of rapid and reliable detection and characterization of airborne pathogenic microorganisms is becoming of exceptional urgency. This project is focused on development of portable first alert bioaerosol monitoring technique utilizing personal bioaerosol sampler capable of high efficient trapping of airborne microorganisms into collecting liquid along with a laser based mini Polymerase Chain Reaction (PCR) machine in a multiplex format (multi-target simultaneous detection) with following identification of minimal time period required for detection of any airborne microbial targets in the ambient air. The experimental program was undertaken under controlled laboratory conditions utilizing of up to 7 plex PCR format for detection of airborne microbial targets in the dynamic aerosol chamber. The technology demonstrated efficient operation and was capable of detecting airborne microbial targets during even shortest experimental sampling periods of 10 s. The total time of detection/analysis was less than 40 min. The proposed sampling timeframe represents realistic scenario of bioaerosol exposure of humans’ moving through areas potentially contaminated by bioaerosol originated from natural or anthropogenic sources. The research outcomes look very promising enabling development of new generation of portable, reliable and fast bioaerosol monitors, which are unique and highly demanded in the areas of defence, public health and others.

Performance of personal electrostatic bioaerosol sampler (PEBS) when collecting airborne microorganisms

We recently developed a new personal electrostatic bioaerosol sampler (PEBS) for determining exposures to airborne microorganisms. PEBS was shown to collect airborne non-biological particles with efficiencies approaching 80% while producing very low ozone concentrations. In this work, we analyzed the performance of this sampler when collecting airborne Bacillus atrophaeus bacterial cells and Penicillium chrysogenum fungal spores as a function of sampling flow rates (e.g., 10 and 20 L/min) and sampling time (e.g., 10, 60, and 240 min). The collected samples were analyzed using microscopy, adenosine triphosphate (ATP)-based bioluminescence, flow cytometry (Live/Dead test), and culture techniques. PEBS's physical and biological performance was compared against that of BioSampler (SKC Inc., Eighty Four, PA) when the samplers were operated at 10 and 12.5 L/min, respectively. PEBS achieved physical collection efficiency as high as 83%, and its physical performance in terms of measured bioaerosol concentration was better than that of BioSampler. In addition, a fraction of live microorganisms recovered by PEBS was not different from that of BioSampler. Compared to BioSampler, PEBS measured similar or higher concentrations of culturable bacteria, but lower concentrations of culturable spores. The airborne ATP concentration measured by PEBS was significantly higher than that measured by BioSampler. Overall, we show that PEBS is a viable and efficient technology to determine personal exposures to airborne microorganisms using multiple sample analysis techniques.

Performances of the BC-112 NIOSH cyclone for the measurement of endotoxins in bioaerosols: A study in laboratory conditions

The BC-112 cyclone is a personal bioaerosol sampler with of a metallic main body (2mm inlet), a first collection stage (1.5mL collection tube) and a final collection stage (37mm three pieces cassette). A laboratory study has been carried out with E. coli experimental bioaerosols in order to investigate the efficiency of the cyclone for the measurement of airborne endotoxins in laboratory conditions. A first set of experiments allowed the validation of a protocol for the removal of endotoxins from contaminated BC-112 cyclones. The study also showed that endotoxins deposited on the inner cassette walls during sampling. Endotoxins deposits accounted for 18–42% of the total endotoxins measured in the bioaerosols and an adaptation of the analytical protocol was necessary in order to take such deposits into account. Furthermore, the type of filter mounted in the cassette significantly (p < 10−4) influenced the concentration of airborne endotoxins measured in the experimental bioaerosol. Teflon and PVC filters led to the highest concentrations while, surprisingly, fiberglass filters led to the lowest ones. An optimal configuration was set for the sampling devices including a PVC filter as collecting medium and extraction of collected endotoxins directly into the cassette. In such a configuration and with our experimental conditions the side by side comparison of the closed-face cassette (CFC) and the BC-112 cyclone showed a significant correlation (r = 0.99; n = 16; p < 10−4) between measurements done with the two sampling devices. The results also highlight that experimental biases may occur when comparing the collection or the overall efficiency of bioaerosol samplers using microbial surrogates and bioaerosol chambers. We concluded that the BC-112 cyclone was suitable for the assessment of airborne endotoxins providing protocol adaptations and that the overall efficiency of the device for the measurement of airborne endotoxins should be investigated in real exposure conditions as well as in other laboratory conditions.

Design and development of a self-contained personal electrostatic bioaerosol sampler (PEBS) with a wire-to-wire charger

ABSTRACTHere, we present a concept of a personal electrostatic bioaerosol sampler (PEBS), which is an open channel collector consisting of a novel wire-to-wire particle charger and a collection section housing a double-sided and removable metal collection plate and two quarter-cylinder ground electrodes. The charger consists of a tungsten wire (25.4 mm long and 0.076 mm in diameter) connected to high voltage and positioned in the center of the charging section (a cylinder 50.8 mm long and 25.4 mm in diameter); a ring of stainless steel wire 0.381 mm in diameter surrounds the hot electrode at its midpoint and is grounded. The newly designed wire-to-wire charger produces lower ozone concentrations compared to traditional wire-to-plate or wire-to-cylinder charger designs. The particles captured on the collection plate are easily eluted using water or other fluids. The sampler was iteratively optimized for optimum charging and collection voltages, and collection electrode geometry. When tested with polystyren...

Multiplexed Surface Plasmon Resonance based real time viral aerosol detection

In the area of environmental bioaerosol monitoring the technologies allowing rapid and precise detection of multiple targets are highly demanded. In our previous feasibility studies we evaluated an applicability of a Surface Plasmon Resonance protocol in conjunction with our personal bioaerosol sampler for rapid detection of airborne viruses and bacteria. It was found that the immunosensor based technique was capable of detecting airborne microbes in a broad range of concentrations within minutes with high accuracy and specificity, even in highly contaminated environments. This project reports the results of the development of a comprehensive technique for simultaneous detection of multiple viral airborne targets in real time. The multiplicity was challenged on detection of two viral objects: MS2 bacteriophage and Influenza A virus. No statistically significant difference in sensitivity between singleplex and multiplex SPR was achieved for both target viruses in aerosol form. The proposed multiplexed technology, based on the direct simultaneous detection of a number of viral aerosols, can be applied to various viral pathogens, and be further realised in a concept of portable “first alert” bioaerosol monitor.

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 ...

The sensitivity of surface plasmon resonance based viral aerosol detection

It is well known that bioaerosols pose hazard to human health. Bioaerosols could be a cause of various severe diseases. Rapid and precise detection of airborne pathogens in different environments has received considerable attention in recent years. Earlier, we explored a Surface Plasmon Resonance (SPR) protocol in conjunction with our recently developed personal bioaerosol sampler for rapid detection of airborne viruses. The developed label-free approach has been verified under controlled laboratory conditions. The immunosensor based technique was capable of detecting airborne virus in a broad range of concentrations within minutes with high accuracy and specificity.This project is a logical continuation of our previous study where we describe the performance evaluation study of two immunosensor types (differed in surface chemistry) for direct viral detection. Common viral surrogate MS2 bacteriophage was employed as a model organism. The detection limits of developed SPR techniques were found to be 1.12×106PFU/mL and 2.2×107PFU/mL for the COOH1 and COOH5 sensor types respectively. Our data confirmed that COOH1 based sensor is more sensitive and robust regarding detection of small viral objects like MS2 phage.The combination of SPR procedure with the bioaerosol sampler allowed detecting virus in the air within less than two minutes. The minimal detectable viral concentration in the air for 1min of sampling time was found to be 1.9×107PFU per litre. Our findings justify that the SPR technique is fully suitable for the bioaerosol monitoring applications. The proposed technology, based on the direct detection of viral aerosols, could be applied to various viral pathogens infectious to animals or humans, and be further realised in a concept of portable real-time bioaerosol monitor.

Evaluation of a novel personal nanoparticle sampler

This work investigated the performance in terms of collection efficiency and aspiration efficiency of a personal sampler capable of collecting ultrafine particles (nanoparticles) in the occupational environment. This sampler consists of a cyclone for respirable particle classification, micro-orifice impactor stages with an acceleration nozzle to achieve nanoparticle classification and a backup filter to collect nanoparticles. Collection efficiencies of the cyclone and impactor stages were determined using monodisperse polystyrene latex and silver particles, respectively. Calibration of the cyclone and impactor stages showed 50% cut-off diameters of 3.95 μm and 94.7 nm meeting the design requirements. Aspiration efficiencies of the sampler were tested in a wind tunnel with wind speeds of 0.5, 1.0, and 1.5 m s(-1). The test samplers were mounted on a full size mannequin with three orientations toward the wind direction (0°, 90°, and 180°). Monodisperse oleic acid aerosols tagged with sodium fluorescein in the size range of 2 to 10 μm were used in the test. For particles smaller than 2 μm, the fluorescent polystyrene latex particles were generated by using nebulizers. For comparison of the aspiration efficiency, a NIOSH two-stage personal bioaerosol sampler was also tested. Results showed that the orientation-averaged aspiration efficiency for both samplers was close to the inhalable fraction curve. However, the direction of wind strongly affected the aspiration efficiency. The results also showed that the aspiration efficiency was not affected by the ratio of free-stream velocity to the velocity through the sampler orifice. Our evaluation showed that the current design of the personal sampler met the designed criteria for collecting nanoparticles ≤100 nm in occupational environments.

Surface plasmon resonance-based real-time bioaerosol detection

Rapid and precise bioaerosol detection in different environments has become an important research and technological issue over last decades. Previously, we employed a real-time PCR protocol in conjunction with personal bioaerosol sampler for rapid detection of airborne viruses. The approach has been proved to be specific and sensitive. However, a period of time required for entire procedure was in manner of hours. Some new developments are required to decrease the detection time down to real-time protocols. Presently, a surface plasmon resonance (SPR)-based immunosensor that coupled with a specific antigen-antibody reaction could offer sensitive, specific, rapid and label-free detection. This study describes the possibility of combining the personal sampler with SPR technology for qualitative and extremely rapid detection of airborne micro-organisms. Common viral surrogate MS2 bacteriophage, frequently used in bioaerosol studies, was employed as a model organism. The results of the sensor functionalizing procedure with monoclonal anti-MS2 antibody and optimization of the chip performance are presented. The SPR-based detection of the airborne virus was found to be very fast; the viral presence was detected in less than 2min, and the entire procedure (sampling and analysis) was undertaken in 6min, which could be considered as real-time detection for this type of measurements. The combination of SPR with the personal sampler targeted towards bioaerosol detection was proven to be feasible. The SPR sensor was found to be highly stable and suitable for multiple utilizations without significant decrease in response. The suggested approach opens new possibilities for the development of portable and rapid (almost real time) bioaerosol monitors. This technology is the first in the world real-time bioaerosol monitor. This outcome would be of strong interest to individuals representing public health, biosecurity, defence forces, environmental sciences and many others.

A wind tunnel test of newly developed personal bioaerosol samplers

In this study, the performance of two newly developed personal bioaerosol samplers was evaluated. The two test samplers are cyclone-based personal samplers that incorporate a recirculating liquid film. The performance evaluations focused on the physical efficiencies that a personal bioaerosol sampler could provide, including aspiration, collection, and capture efficiencies. The evaluation tests were carried out in a wind tunnel, and the test personal samplers were mounted on the chest of a full-size manikin placed in the test chamber of the wind tunnel. Monodisperse fluorescent aerosols ranging from 0.5 to 20 μm were used to challenge the samplers. Two wind speeds of 0.5 and 2.0 m/sec were employed as the test wind speeds in this study. The test results indicated that the aspiration efficiency of the two test samplers closely agreed with the ACGIH inhalable convention within the size range of the test aerosols. The aspiration efficiency was found to be independent of the sampling orientation. The collection efficiency acquired from these two samplers showed that the 50% cutoff diameters were both around 0.6 μm. However, the wall loss of these two test samplers increased as the aerosol size increased, and the wall loss of PAS-4 was considerably higher than that of PAS-5, especially in the aerosol size larger than 5 μm, which resulted in PAS-4 having a relatively lower capture efficiency than PAS-5. Overall, the PAS-5 is considered a better personal bioaerosol sampler than the PAS-4. Implications: Detection of personal exposure to airborne microorganisms (bioaerosols) is essential for developing adequate environmental and occupational air monitoring programs. Recently, two liquid-cyclone-based personal bioaerosol samplers were developed for this purpose. This study is to evaluate the performance of these two newly developed samplers in terms of their physical sampling efficiencies, such as the aspiration, collection, and capture efficiencies. The results acquired can offer insight into the efficacy of the newly designed samplers on achieving the goal of providing reliable and accurate personal bioaerosol exposure assessment.

Internally controlled PCR system for detection of airborne microorganisms

Recently, we reported the outcomes of feasibility studies of a technological approach allowing rapid detection of a wide range of bioaerosols by combining a personal bioaerosol sampler with a real-time PCR technology. The protocol was found suitable for detection of targeted microorganisms within relatively short time periods. Considering the crucial importance of the PCR procedure quality control, the current paper reports the results of the development of an internally controlled PCR system for utilization by the above technology. The suggested strategy is based on utilization of only two fluorescent dyes, which are used respectively for target and internal amplification control (IAC) DNA amplification. A bacteriophage T4 and recombinant phage fd (M13) were used in this research as target and IAC, respectively. The constructed IAC was added directly to the collection liquid of the personal bioaerosol sampler enabling quality control to be present throughout the entire sampling-analysis procedures. For performance evaluation, serial ten-fold dilutions of T4 phage were aerosolized and sampled over a 10 minutes time period. The results showed that T4 phage could be reliably detected at the concentration of around 200 PFU per litre of air over the 10 minutes sampling period. The developed PCR assay demonstrated high specificity and no cross reaction. It is concluded that the recombinant phage fd is suitable for utilization as an internal control enabling to significantly minimize false negative results for bioaerosol detection procedures.

Development of a Personal Bioaerosol Sampler Based on a Conical Cyclone with Recirculating Liquid Film

This article describes the development of a novel, high-performance personal aerosol sampler intended to monitor occupational air pollution, specifically, microbial constituents. This prototype sampler has a horizontally positioned conical cyclone with recirculating liquid film and an ejection supply of adsorptive liquid into the inlet nozzle. Airborne pollutants were collected in the adsorptive liquid, thus improving the survivability of microbiological aerosol samples. Experimental modules of different dimensions were first evaluated. Based on the test results, a prototype sampler was fabricated and tested. Evaluation of the collection efficiency of the prototype unit indicated a higher than 90% collection efficiency for particles > 1.0 μ m. The 50% cutoff diameter was between 0.70–0.75 μ m. For assessment of the sampling process effect on the collected microorganisms, Bacillus thuringiensis was tested at a concentration of about 1.0 × 106 cells per cm3. The viability in the prototype sampler decreased to 78% after 60 min of operation.

Development of a new procedure for precise determination of viral aerosol lethal dose (ALD 50) for birds

This paper describes a new method for precise determination of viral aerosol lethal dose (ALD 50) and reports the results obtained for birds exposed by H5N1 Avian influenza A strain under controlled laboratory conditions. The reported method utilizes our recently developed personal bioaerosol sampler capable of monitoring viable virus concentration in the ambient air. Up to six laboratory animals could be located in a specially designed aerosol chamber and exposed in parallel by an airborne strain of interest to generate the amount of data sufficient for representative statistical analysis. A concentration of viable airborne virus was measured by the personal aerosol samplers directly in the breathing zone of each particular bird. The results show a very low inter-sampler variation used for each particular run, which was confirmed by a single factor ANOVA test undertaken for all six personal samplers involved in each experiment. As was shown, the difference in amount of viruses collected by all samplers during each particular run was not statistically significant. It was found that the ALD 50 for approximately 400-g birds exposed to H5N1 Avian influenza A strain A/Chicken/Suzdalka/Nov-11/2005 was around 26.5 FFU (focus forming units).

Monitoring of Airborne Mumps and Measles Viruses in a Hospital

AbstractA new personal bioaerosol sampler, which was found suitable for continuous long‐term (up to 8 h) monitoring of airborne bacteria, fungi, and viruses, was recently developed. A range of investigations under controlled laboratory conditions verified the performance of the device for both stress sensitive and robust viral particles. To decrease the detection time, the next step of the technique development was related to utilization of the sampler in combination with polymerase chain reaction (PCR) technology in the laboratory. The combined device was found to be fully feasible with the corresponding decrease of the detection time from a few days to 2.5 h. In addition, the results for targeted microorganisms were not affected by background biological particles and cross‐reaction was not observed. The current study is the first trial to use the new combined device, i. e., sampler‐conventional PCR device, for monitoring airborne viruses in the field. The monitoring procedures were performed in hospital infection wards with patients suffering from mumps and measles diseases to detect the corresponding disease causing viruses in the ambient air. The results for the existence of the airborne viruses were obtained for both strains. A simple procedure is also suggested for enumeration of microbial contamination in the ambient air.

Bioaerosol sampling for the detection of aerosolized influenza virus.

Background Influenza virus was used to characterize the efficacy of a cyclone‐based, two‐stage personal bioaerosol sampler for the collection and size fractionation of aerosolized viral particles. Methods A Collison single‐jet nebulizer was used to aerosolize the attenuated FluMist® vaccine into a calm‐air settling chamber. Viral particles were captured with bioaerosol samplers that utilize 2 microcentrifuge tubes to collect airborne particulates. The first tube (T1) collects particles greater than 1.8 μm in diameter, while the second tube (T2) collects particles between 1.0 and 1.8 μm, and the back‐up filter (F) collects submicron particles. Following aerosolization, quantitative PCR was used to detect and quantify H1N1 and H3N2 influenza strains. Results Based on qPCR results, we demonstrate that aerosolized viral particles were efficiently collected and separated according to aerodynamic size using the two‐stage bioaerosol sampler. Most viral particles were collected in T2 (1‐1.8 μm) and on the back‐up filter (< 1 μm) of the bioaerosol sampler. Furthermore, we found that the detection of viral particles with the two‐stage sampler was directly proportional to the collection time. Consequently, viral particle counts were significantly greater at 40 minutes in comparison to 5, 10 and 20 minute aerosol collection points. Conclusions Due to a lack of empirical data, aerosol transmission of influenza is often questioned. Using FluMist®, we demonstrated that a newly developed bioaerosol sampler is able to recover and size fractionate aerosolized viral particles. This sampler should be an important tool for studying viral transmission in clinical settings and may significantly contribute towards understanding the modes of influenza virus transmission.

Personal Sampler for Viable Airborne Microorganisms: Main Development Stages

AbstractA new personal bioaerosol sampler has been developed and verified as an efficient tool for monitoring of viable/non‐viable airborne microorganisms, including bacteria, fungi, and viruses. The operational principle of the device is based on continuous passage of an air sample through porous media submerged into a liquid layer. During motion along narrow and tortuous ways inside the porous media, the air stream is split into a large number of ultra small bubbles with the particulates are being scavenged by these bubbles and, thus, effectively trapped. The device was initially verified for monitoring of viable airborne bacteria and fungi, firstly, under controlled laboratory conditions and later in a field. It was demonstrated that bacterial recovery rates for these two groups of microorganisms were very high and the device was found to be fully feasible for such monitoring. The next step of the device investigation was performed in the laboratory on monitoring viable airborne viruses with a range of sensitivities to physical and biological stresses. As the result, the new personal sampler demonstrated a very high recovery rate even for viruses which are rather sensitive to environmental stress (Avian Influenza, SARS, Mumps, etc.). Some following field studies, undertook in a hospital and animal houses, also demonstrated an excellent performance of the new device for selective and reliable monitoring of viable airborne viruses even in environments highly contaminated by other microorganisms. This paper reviews the main development staged of the new personal bioaerosol sampler.

Personal Sampler for Monitoring of Viable Viruses; Modeling of Indoor Sampling Conditions

This article describes the development of a mathematical model for evaluation of particle concentration for indoor air conditions. The results of modeling could be used to predict particle concentration in an ambient air at different distances from the source, taking into account space geometry and ventilation/air conditioning created air streams. Two case studies were then undertaken to determine the particle concentration at hypothetical shopping center for the situations when: (1) the ambient air movement is created by a local ventilation system, and (2) besides the local ventilation, the outdoor air enters the space influencing particle distribution situation due to mixing with ventilation created air streams. The results of modeling were used to evaluate the minimal source concentration of virus containing aerosols measurable by our recently developed personal bioaerosol sampler moving along various routes during certain time intervals.

Personal sampler for monitoring of viable viruses; modelling of outdoor sampling conditions

A new personal bioaerosol sampler has recently been developed and verified to be very efficient for monitoring of viable airborne bacteria, fungi and viruses. The device is capable of providing high recovery rates even for microorganisms which are rather sensitive to physical and biological stresses. However, some mathematical procedure is required for realistic calculation of an actual concentration of viable bioaerosols in the air taking into account a rate of inactivation of targeted microorganisms, sampling parameters, and results of microbial analysis of collecting liquid from the sampler. In this paper, we develop such procedure along with the model of aerosol propagation for outdoor conditions. Combining these procedures allows one to determine the optimal sampling locations for the best possible coverage of the area to be monitored. A hypothetical episode concerned with terrorists’ attack during music concert in the central square of Novosibirsk, Russia was considered to evaluate possible coverage of the area by sampling equipment to detect bioaerosols at various locations within the square. It was found that, for chosen bioaerosol generation parameters and weather conditions, the new personal sampler would be capable to reliably detect pathogens at all locations occupied by crowd, even at distances of up to 600 m from the source.

Rapid detection of airborne viruses by personal bioaerosol sampler combined with the PCR device

A new personal sampler had been previously developed and verified for monitoring of viable airborne viruses. The aims of this project were to investigate a possibility of the utilization of the polymerase chain reaction (PCR) method to speed up the time consuming analytical procedures and to evaluate a lower detection limit of the combined (sampler-PCR) device. Tenfold serial dilutions of the initial suspension of the Vaccinia virus were aerosolized in the chamber and airborne viruses were monitored by two simultaneously operating samplers. The results of monitoring were successfully obtained by a standard plaque assay (live microbes) and by the PCR method (total DNA). The corresponding calculations to identify the minimal detectable concentration in the ambient air were then performed. It was found that the minimal detectable concentration of airborne viruses in the ambient air depends on the sampling time. As demonstrated, such concentration should be at least 125×10 3 PFU m −3 for a sampling time of as short as 1 min. The detectable concentration decreases with the increase of the sampling time and reaches 25×10 3 and 10×10 3 PFU m −3 for 5 and 12.5 min of sampling respectively.

Bioaerosol sampling by a personal rotating cup sampler CIP 10-M

High concentrations of bioaerosols containing bacterial, fungal and biotoxinic matter are encountered in many workplaces, e.g. solid waste treatment plants, waste water treatment plants and sewage networks. A personal bioaerosol sampler, the CIP 10-M (M-microbiologic), has been developed to measure worker exposure to airborne biological agents. This sampler is battery operated; it is light and easy to wear and offers full work shift autonomy. It can sample much higher concentrations than biological impactors and limits the mechanical stress on the microorganisms. Biological particles are collected in 2 ml of liquid medium inside a rotating cup fitted with radial vanes to maintain an air flow rate of 10 l min(-1) at a rotational speed of approximately 7,000 rpm. The rotating cup is made of sterilisable material. The sampled particles follow a helicoidal trajectory as they are pushed to the surface of the liquid by centrifugal force, which creates a thin vertical liquid layer. Sterile water or another collecting liquid can be used. Three particle size selectors allow health-related aerosol fractions to be sampled according to international conventions. The sampled microbiological particles can be easily recovered for counting, incubation or further biochemical analysis, e.g., for airborne endotoxins. Its physical sampling efficiency was laboratory tested and field trials were carried out in industrial waste management conditions. The results indicate satisfactory collection efficiency, whilst experimental application has demonstrated the usefulness of the CIP 10-M personal sampler for individual bioaerosol exposure monitoring.