Filtering the invisible: New evidence points to more efficient indoor air microbe sampling

Using fluorescence-based detection, the study provides clear, quantitative evidence that sampling principle, collection medium, and airflow rate strongly shape how well indoor microbial aerosols can be measured.
Global outbreaks such as SARS, H1N1 influenza, MERS, and COVID-19 have highlighted the importance of understanding how pathogens travel through indoor air. Microbial aerosols—including bacteria, fungi, and viruses—can remain suspended for long periods, increasing exposure risks in enclosed spaces. Air samplers are essential tools for monitoring these hazards, but their performance varies widely. Previous studies have often relied on a single sampler type or focused on biological recovery alone, making direct comparisons difficult. Moreover, traditional culture-based or molecular methods are time-consuming and can underestimate true airborne concentrations. Fluorescence-based techniques offer a faster alternative by directly quantifying captured particles without the need for cultivation or genetic amplification.
A study (DOI:10.48130/biocontam-0025-0011) published in Biocontaminant on 28 November 2025 by Zhen Ding’s team, Jiangsu Center for Disease Control and Prevention, systematically compares air sampling principles, collection media, and flow rates, demonstrating the superior physical capture performance of membrane filtration for submicron indoor microbial aerosols and providing critical technical guidance for accurate airborne pathogen monitoring.
Using a controlled chamber setup, the study compared four common microbial aerosol sampling principles—liquid impinger, dry-wall cyclone, wet-wall cyclone, and membrane filtration—by aerosolizing 0.3 μm and 1 μm polystyrene fluorescent microspheres as standardized surrogates for virus- and bacteria-bearing particles, then quantifying recovered material via fluorescence intensity. To isolate how operational choices shape collection, the team also tested different sampling media (PBS, RNase-free water, irradiated physiological saline) for the liquid-based samplers and varied flow rates across devices (membrane filtration: 30–50 L/min; wet-wall cyclone: 100–300 L/min). Results showed that sampling principle strongly determined performance: membrane filtration produced markedly higher fluorescence signals than the other samplers, corresponding to a sampling efficiency about four to six times higher for 0.3 μm microspheres and five to ten times higher for 1 μm microspheres than the liquid impinger, dry-wall cyclone, and wet-wall cyclone. Sampling medium further modulated recovery among liquid-based devices, with PBS consistently yielding the highest fluorescence intensities; for 0.3 μm particles, PBS increased fluorescence by ~4.94% (vs RNase-free water) and 8.91% (vs irradiated saline) for the impinger, and by 34.38% and 31.34% for the dry-wall cyclone (both statistically significant), while the wet-wall cyclone showed PBS advantages across 100–300 L/min (generally ~4–7% vs RNase-free water and up to ~23% vs irradiated saline depending on flow). Similar PBS-driven gains were observed for 1 μm particles (e.g., ~5–6% for the impinger and ~35–37% for the dry-wall cyclone). Flow rate effects were device-specific: membrane filtration fluorescence increased with higher flow, peaking at 50 L/min (virus surrogate +33.97% vs 30 L/min; +25.92% vs 40 L/min; bacteria surrogate +34.65% and +21.46%), whereas the wet-wall cyclone improved from 100 to 250 L/min but declined at 300 L/min, consistent with high-flow losses. Physical sampling efficiencies also rose with particle size across samplers (impinger: 8.83%→19.25%; dry-wall cyclone: 6.98%→19.56% from 0.3 to 1 μm), yet none exceeded 50%, preventing Da50 determination for all devices under tested conditions.
These findings provide practical guidance for indoor air quality monitoring, infection control, and exposure assessment. Membrane filtration samplers emerge as a robust option for mechanically collecting submicron aerosols in both research and surveillance settings. For liquid-based systems, PBS is recommended as a standard collection medium. The results can inform the design of monitoring programs in hospitals, schools, public transport, and other high-risk indoor environments where accurate assessment of airborne microbes is essential.

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References

DOI

10.48130/biocontam-0025-0011

Original Source URL

https://doi.org/10.48130/biocontam-0025-0011

Funding information

This work was supported by the Medical Science and Research Project funded by the Jiangsu Commission of Health (Grant Nos ZD2021021 and M2022069).

About Biocontaminant

Biocontaminant is a multidisciplinary platform dedicated to advancing fundamental and applied research on biological contaminants across diverse environments and systems. The journal serves as an innovative, efficient, and professional forum for global researchers to disseminate findings in this rapidly evolving field.