Comparative Testing and Evaluation of Nine Different Air Samplers: End-to-End Sampling Efficiencies as Specific Performance Measurements for Bioaerosol Applications

Figures & data

TABLE 1 Air sampling equipment subjected to comparative testing and evaluation (T&E) in this study

				Liquid	Theoretical		Collection/	Additional
			Airflow	sample	relative		extraction	equipment
		Collection	rate	volume	concentration	Consumables	liquid	needs
Air sampler	Manufacturer	principle	(l min^−1)	(ml)^a	factor^b	(in this study)	(in this study)	(in this study)
BioSampler	SKC (Eighty Four, PA, USA)	Liquid impingment (swirling liquid impingment)	12.5	19	Reference sampler		PBSTA	Vacuum pump (Picolino VTE 3, Gardner Denver Thomas, Sheboygan, WI) and liquid trap (SKC)
Gelatin filters	SKC	Filtration (gelatin filter)	15	10	2	Gelatin filters (3 μm pore size, 37 mm) with cellulose backing filters housed in conductive polypropylene filter cassettes	PBSTA	Vacuum pump (Picolino VTE 3) and flow restrictor (SKC)
SASS 2300	Research International (Monroe, WA, USA)	Cyclonic separation/liquid impingment (wetted-wall cyclone)	390	4	148		PBS^c
SASS 3100	Research International	Filtration (electret filter)	300	7.5	61	Electret filters	PBSTA	SASS 3010 filter extractor unit (Research International)
Coriolis FR	Bertin Technologies (Montigny-le-Bretonneux, France)	Cyclonic separation/liquid impingment (wet cyclone)	300	9	51	Cyclones	PBS-based surfactant-containing commercial formulation
OMNI-3000	InnovaPrep (Drexel, MO, USA)	Cyclonic separation/liquid impingment (contactor/wetted-wall cyclone)	300	10	46	Cartridges for collection liquid injection and sample output	PBS^c
BioCapture 650	FLIR Systems (Arlington, VA, USA)	Impaction (spinning disk)	200	5	61	Collection cartridges with integrated spinning disk, tubing, extraction liquid reservoir, and sample output vial	PBS-based surfactant-containing commercial formulation
ESP (prototype)	Dycor Technologies (Edmonton, AB, Canada)	Electrostatic precipitation	540	10	82	Collection pipes	PBSTA
XMX-CV	Dycor Technologies	Liquid impingment^d	530	4	201	Collection vials	PBSTA
PBS, phosphate buffered saline; PBSTA, PBS supplemented with 0.05% Triton X-100 (Sigma-Aldrich, St. Louis, MO, USA) and 0.005% Antifoam A (Sigma–Aldrich).
^aThe reported value is the typical liquid volume recovered from the air sampler after 5 min of operation (20°C and 55% RH). For samplers that did not directly output a liquid sample (gelatin filters, SASS 3100, and ESP), the reported value is the typical liquid volume recovered after sample-to-liquid extraction.
^bThe air sampler's theoretical concentration factor (air to liquid) calculated relative to the reference sampler.
^cThe SASS 2300 and OMNI-3000 were not compatible with surfactant-based collection liquids. The samples were supplemented with 0.05% Triton X-100 (Sigma–Aldrich) and 0.005% Antifoam A (Sigma-Aldrich) after sampling.
^dThe XMX-CV may also be used with a filter cassette (filtration) instead of the collection vial (liquid impingment). Only the liquid impingment option was evaluated as part of this study.

FIG. 1 The evaluated air samplers’ end-to-end cultivation-based biological sampling efficiencies (BSEs) and qPCR- or fluorescence microscopy-based physical sampling efficiencies (PSEs) relative to a reference sampler (BioSampler) for 1 and 4 μm mass median aerodynamic diameter (MMAD) aerosols of FluoSpheres (FS) and B. atrophaeus spores (BG). The evaluated air samplers’ sampling efficiencies were significantly different from the BioSampler's sampling efficiency (gray dotted line) except when specified with an asterisk (*). The evaluated air samplers’ sampling efficiencies were significantly different for 1 μm aerosols compared to 4 μm aerosols when specified with the same letter.

FIG. 2 The evaluated air samplers’ end-to-end cultivation-based biological sampling efficiencies (BSEs, upper panel) and qPCR-based physical sampling efficiencies (PSEs, lower panel) relative to the reference sampler (BioSampler) for 4 μm mass median aerodynamic diameter (MMAD) aerosols of B. atrophaeus spores (BG), Kocuria rhizophila (KR), Serratia marsescens (SM), and bacteriophage MS2 (MS2). The evaluated air samplers’ sampling efficiencies were significantly different from the BioSampler's sampling efficiency (gray dotted line) except when specified with an asterisk (*). The evaluated air samplers’ BSEs and PSEs were significantly different from each other when specified with the same letter.

TABLE 2 Generalized features regarding the evaluated air samplers’ suitability for various bioaerosol sampling applications

Bioaerosol sampling applications		Gelatin filters	SASS 2300	SASS 3100	Coriolis FR	OMNI-3000	BioCapture 650	ESP prototype	XMX-CV
Quantitative sampling (suitability requirement: relative sampling efficiency ≥0.5 compared to the BioSampler)^a	Particle size (1 μm and 4 μm) (determined for FS and BG aerosols)	Both sizes	None	Both sizes	Both sizes (∼0.5 for 1 μm)	None	4 μm only	4 μm only (∼0.5 for 4 μm)	4 μm only
	PSE-dependent analysis method (e.g., qPCR) (determined for 4 μm FS, BG, KR, SM, and MS2 aerosols)	FS, BG, KR and SM	SM and MS2	All agents	All agents (∼0.5 for MS2)	None^b	All agents (∼0.5 for SM)	FS, BG and KR (∼0.5 for FS)	FS, BG, KR and SM
	BSE-dependent analysis method (e.g., cultivation) (determined for 4 μm BG, KR, SM, and MS2 aerosols)	BG, KR, and MS2	KR, SM, and MS2	BG and KR	All agents	None^b	BG, KR, and MS2	BG and KR (∼0.5 for both)	BG, KR, and SM
Qualitative sampling (suitability requirement: relative concentration factor ≥1.0 compared to the BioSampler)^c	Particle size (1 μm and 4 μm) (determined for FS and BG aerosols)	Both sizes	Both sizes	Both sizes	Both sizes	Both sizes based on BG, only 4 μm based on FS	Both sizes	Both sizes	Both sizes
	PCF-dependent analysis method (e.g., PCR-based detection) (determined for 4 μm FS, BG, KR, SM, and MS2 aerosols)	FS, BG, KR, and SM	All agents	All agents	All agents	BG and FS^b	All agents	All agents	All agents
	BCF-dependent analysis method (e.g., cultivation-based detection) (determined for 4 μm BG, KR, SM, and MS2 aerosols)	BG, KR, and MS2	All agents	BG, KR, and MS2 (∼1.0 for MS2)	All agents	BG^b	All agents	All agents	All agents
BSE: Biological sampling efficiency; PSE: physical sampling efficiency; BCF: biological concentration factor; PCF: physical concentration factor; FS: FluoSpheres; BG: Bacillus atrophaeus spores; KR: Kocuria rhizophila; SM: Serratia marcescens; MS2: Bacteriophage MS2.
^aAn air sampler was assessed suitable for quantitative applications when its relative sampling efficiency was ≥0.5 (i.e., less than two-fold underestimation of the concentration level compared to the BioSampler).
^bThe OMNI-3000 was not tested with 4 μm KR, SM, and MS2 aerosols.
^cAn air sampler was assessed suitable for qualitative applications when its relative concentration factor was ≥1.0 (i.e., similar or higher concentration of sampled material available for the downstream analysis compared to the BioSampler).