Highly Enriched, Controllable, Continuous Aerosol Sampling Using Inertial Microfluidics and Its Application to Real-Time Detection of Airborne Bacteria

Abstract

We report a novel microfluidic technique for sampling of aerosols into liquids. The two-phase fluid, sampling air and collecting liquid, forms a stratified flow in the curved microchannel. By passing fluids through the curved region, the particles are transferred from air into the liquid phase by the particle centrifugal and drag forces. This microfluidic-based aerosol-into-liquid sampling system, called the MicroSampler, is driven by particle inertial differences. To evaluate the physical particle collection efficiency of the MicroSampler, we used standard polystyrene-latex (PSL) particles ranging in size from 0.6 to 2.1 μm and measured particle concentrations upstream and downstream of the MicroSampler with an aerodynamic particle sizer. The cutoff diameter of particle collection was selected controlling the air flow velocity (microfluidic air flow of 0.6 L/min showed a particle collection efficiency of ∼98% at a particle diameter of 1 μm), and continuous enriched particle sampling was possible for real-time postprocessing application. With regard to biological collection efficiency, the MicroSampler showed superior microbial recovery (Staphylococcus epidermidis) compared to the conventional BioSampler technique. These results indicate that our MicroSampler can be used as a portable, cost-effective, simple, and continuous airborne microorganism collector for applications in real-time bioaerosol detection.

Real-time sensing of bioaerosols: Review and current perspectives

“…Microfluidics techniques are based on controlled manipulations of femtoliter to microliter fluid volumes, often in a lab-on-a-chip environment. Microfluidic devices aimed at bioaerosol detection have recently been developed (Choi et al 2017;Novosselov et al 2014), usually consisting of a collector, delivering bioaerosols into microfluidic liquid volumes, integrated with a biological assay. Aerosol is collected via impaction into microdroplets, directing aerosols into winding microchannels of a chip, or depositing aerosols onto a small substrate for later recovery (Foat et al 2016;Han, An, and Mainelis 2010).…”

Development of an automated wet-cyclone system for rapid, continuous and enriched bioaerosol sampling and its application to real-time detection

“…The collection vessel was filled with a liquid collection medium (20 mL). The nozzles of the BioSampler create a swirling air flow (12.5 L/min air of air supply) that maintains microorganism viability by gently moving particles onto the collection surface without re-aerosolization [25,[37][38][39]. Under the same bioaerosol exposure condition (∼ 100 particles/cm 3 air of total aerosol number concentration (TANC)), we sampled the bioaerosols using the ARBSW and BioSampler and obtained the culturable bioaerosol number concentration, respectively.…”

“…The influence of air flow on a liquid film can be expressed by the modified Webber number, We m . This can be conceived of as a measure of the relative importance of the inertia of a fluid compared to its surface tension [25]:…”

“…A comparative test was conducted with the conventional verified bioaerosol sampler, called BioSampler, which has a collection efficiency of > 90% for bioaerosol sizes of > 0.5 μm and a microbial recovery of > 99%. According to the BioSampler's operational manual, 12.5 L/min of air enters 20 mL of sampling liquid in a reservoir and the enrichment of the collected particles is proportional to the sampling time (typically 20 min to reduce the desiccation effect) [25,[37][38][39]. In contrast, the ARBSW system maintains a high particle enrichment ratio regardless of the sampling time, due to the constant air-to-liquid flow rate ratio (∼ 1.4 × 10 5 ; use of the continuous entered air flow (16 L/min) and drainage liquid flow (7 mL/h)).…”

“…Liu et al and other researchers described an airborne pathogen direct analysis system based on microfluidic enrichment [11][12][13]; however, these systems require prolonged sampling for enrichment. A novel bioaerosol sampling system, the MicroSampler, based on two-phase fluid control in a microchip can be used with a real-time bioaerosol sensor [25]; however, due to the low throughput, adequate sampling is difficult in the presence of bioaerosol concentrations < 500 CFU/m 3 air . A wet-cyclone collects aerosols into a liquid film on the inner wall of the cyclone using the particle centrifugal force and the liquid surface tension.…”