Bioaerosols - Aerosols: Measurement, Dosimetry, and Health Effects - page 323

12.6.3.4 Future Directions in Bioaerosol Sampling
Several real-time instruments for bioaerosol measurement are under development, primarily for
biodefense applications. Four models of direct-reading instruments currently are available com-
mercially. The irst commercial unit was the ultraviolet aerodynamic particle size spectrome-
ter (UV-APS, time-of-light spectrometer, Table 12.2). The biological origin of the particle is
conirmed by detection of ultraviolet irradiation-induced luorescence. UV-APS relies on opti-
cal detection of particles; thus, its use is not feasible for particles <0.1 μm. Furthermore, luo-
rophores decay after microbial death, thus, UV-APS is best suited for measurement of viable
microorganisms. 360,361
Three other real-time instruments are modiications of the UV-APS (FLAPS-III, IBAC
Biological Aerosol Threat Monitor, and Vero Tect Bio-detector; Table 12.2). FLAPS-III measures
particle size using light scattering and luorescence emission at two distinct wavelengths, which
increases speciicity for biological particles. The IBAC has been made rugged and packaged for
military applications. It can be connected to a concentrator and used as a trigger for a secondary
aerosol sampler with subsequent identiication of biological particles. The Vero Tect Bio-detector
measures particle shape in addition to measuring the particle size and luorescence emission at two
wavelengths.
Many near real-time instruments take advantage of the progress in analytical methods that can
provide results within minutes. One instrument collects aerosol particles for a predeined period
onto a low-luorescence substrate (AirSentinel, Table 12.2). The spot is exposed to UV excitation
and the emitted luorescence is detected. After each collect-spot-interrogate cycle is completed, the
collection substrate is regenerated to its original condition and a new cycle can begin. Wetted wall
cyclones with continuous liquid outlow can be connected to a bioassay unit that is more speciic
than intrinsic luorescence, for example, immunoassay or PCR. 362 However, a concentrated aerosol
is required for these samplers to achieve suficient sensitivity. The EPSS can transfer particles into
water droplets as small as 5 μL and achieve concentration rates of up to 10 6 . 358
Many conventional samplers take advantage of non-culture methods for bioaerosol analysis,
and personal sampling is becoming more convenient for individual exposure measurement. For
example, personal samplers have been used to quantify viruses with real-time PCR. 277,363 An uncon-
ventional personal sampler its into a test subject's nostrils (Intra-nasal air sampler, INAS) and has
been used to measure allergen and fungal exposures. 209 Several particle sensors under development
eventually may be adapted to biological particle detection, for example, an array biosensor that can
interrogate multiple samples simultaneously for multiple targets has been miniaturized and auto-
mated for portability and on-site use by untrained persons. 364

12.6.4 s aMPle a nalysis

12.6.4.1 Microscopy
Light microscopy still is one of the most powerful methods available for the qualitative and quantita-
tive analysis of those pollen grains and fungal spores that have unique morphological features. The
lower limit of resolution for this method is 1 μm. Quality control evaluations using an intercalibra-
tion test for airborne pollen monitoring demonstrated the important role of operator training and the
need for standards in pollen sample analysis by microscope. 365 The British Aerobiology Federation,
the Pan-American Aerobiology Association, the Italian Organization for Standardization, and the
American Society for Testing and Materials have published standard methods for counting pol-
len grains and fungal spores. 366-369 An evaluation of the Italian method found that for the same
sample size, conidence intervals vary in relation to pollen abundance in terms of number of grains
or species. 370 The sample size suggested by the standard (20% of the target surface) may result in
errors in pollen counts ranging from 7% to 55% of the mean value, and in missing 22%-54% of the
taxa present on a slide.