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

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

Development of a Novel Electrostatic Precipitator System Using a Wet-Porous Electrode Array

<div><p>The authors introduce a novel electrostatic precipitator using a wet-porous electrode (WPE) array, for application to various work processes (e.g., molding and extrusion), to improve the removal performance of ultrafine particles and water-soluble gaseous pollutants generated during manufacturing. The WPE array electrostatic precipitator (WPE-ESP) consists of an ionization component for particle charging and a collection component equipped with the WPE array to maintain a high humidity environment. The performance of the WPE-ESP was evaluated in terms of the removal efficiency of airborne particles and water-soluble gases under ESP operating conditions in which the ionization charge current, the applied electric field strength of the collection component, and the relative humidity (RH) were varied. The collection efficiency of the WPE-ESP was enhanced by increasing the RH, due to water adsorption on the particle surface and the enhanced electric field strength near the collecting plate. The maximum total collection efficiency of the ESP system was ˜99.2% for a 73% RH collection environment, which was approximately 3.3% higher than that of conventional dry-type ESP (C-ESP). The proposed system also removed sulfur dioxide (SO₂), a representative source (90.7%) of undesirable emissions during manufacturing processes, and mitigated ozone (O_3, <10 ppb), a by-product of the corona discharge in the ESP, regardless of the field strength. The proposed WPE-ESP included a simple mounting system; additionally, the system generated a more uniform water film than that of wet-ESPs. Thus, the WPE-ESP shows great potential for application to workplaces and machining devices that require the simultaneous removal of ultrafine particles and water-soluble gaseous pollutants.</p><p>Copyright 2015 American Association for Aerosol Research</p></div

Antimicrobial Air Filters Using Natural <i>Euscaphis japonica</i> Nanoparticles

<div><p>Controlling bioaerosols has become more important with increasing participation in indoor activities. Treatments using natural-product nanomaterials are a promising technique because of their relatively low toxicity compared to inorganic nanomaterials such as silver nanoparticles or carbon nanotubes. In this study, antimicrobial filters were fabricated from natural <i>Euscaphis japonica</i> nanoparticles, which were produced by nebulizing <i>E</i>. <i>japonica</i> extract. The coated filters were assessed in terms of pressure drop, antimicrobial activity, filtration efficiency, major chemical components, and cytotoxicity. Pressure drop and antimicrobial activity increased as a function of nanoparticle deposition time (590, 855, and 1150 µg/cm2_filter at 3-, 6-, and 9-min depositions, respectively). In filter tests, the antimicrobial efficacy was greater against <i>Staphylococcus epidermidis</i> than <i>Micrococcus luteus</i>; ~61, ~73, and ~82% of <i>M</i>. <i>luteus</i> cells were inactivated on filters that had been coated for 3, 6, and 9 min, respectively, while the corresponding values were ~78, ~88, and ~94% with <i>S</i>. <i>epidermidis</i>. Although statistically significant differences in filtration performance were not observed between samples as a function of deposition time, the average filtration efficacy was slightly higher for <i>S</i>. <i>epidermidis</i> aerosols (~97%) than for <i>M</i>. <i>luteus</i> aerosols (~95%). High-performance liquid chromatography (HPLC) and electrospray ionization-tandem mass spectrometry (ESI/MS) analyses confirmed that the major chemical compounds in the <i>E</i>. <i>japonica</i> extract were 1(ß)-<i>O</i>-galloyl pedunculagin, quercetin-3-<i>O</i>-glucuronide, and kaempferol-3-<i>O</i>-glucoside. <i>In vitro</i> cytotoxicity and disk diffusion tests showed that <i>E</i>. <i>japonica</i> nanoparticles were less toxic and exhibited stronger antimicrobial activity toward some bacterial strains than a reference soluble nickel compound, which is classified as a human carcinogen. This study provides valuable information for the development of a bioaerosol control system that is environmental friendly and suitable for use in indoor environments.</p></div

Concentrations, GSD, GMD, and peak diameters of test bacterial bioaerosols (<i>n</i> = 3).

<p>¹GSD, geometric standard deviation.</p><p>²GMD, geometric mean diameter.</p><p>Concentrations, GSD, GMD, and peak diameters of test bacterial bioaerosols (<i>n</i> = 3).</p

The inactivation rate of <i>E</i>. <i>japonica</i> extract nanoparticles-coated filters on bacterial aerosols.

<p>Error bars indicate standard deviations (<i>n</i> = 3).</p

The inhibitory effects of <i>E</i>. <i>japonica</i> and a soluble nickel compound (SNC) on A549 cancer and HEL 299 cells.

<p>Error bars indicate standard deviations (<i>n</i> = 10) ¹Half maximal inhibitory concentration, ²A549 human lung adenocarcinoma cancer cells, ³HEL 299 human lung fibroblast cells.</p

The pressure drop through the antimicrobial air filters is shown as a function of particle deposition conditions.

<p>Error bars indicate standard deviations (<i>n</i> = 3).</p

A comparison of the antimicrobial activity of <i>E</i>. <i>japonica</i> and SNC using the disk diffusion method (<i>n</i> = 5).

<p>A comparison of the antimicrobial activity of <i>E</i>. <i>japonica</i> and SNC using the disk diffusion method (<i>n</i> = 5).</p

Al-Coated Conductive Fibrous Filter with Low Pressure Drop for Efficient Electrostatic Capture of Ultrafine Particulate Pollutants

Here, we demonstrate a new strategy of air filtration based on an Al-coated conductive fibrous filter for high efficient nanoparticulate removals. The conductive fibrous filter was fabricated by a direct decomposition of Al precursor ink, AlH₃{O­(C₄H₉)₂}, onto surfaces of a polyester air filter via a cost-effective and scalable solution-dipping process. The prepared conductive filters showed a low sheet resistance (<1.0 Ω sq^–1), robust mechanical durability and high oxidative stability. By electrostatic force between the charged fibers and particles, the ultrafine particles of 30–400 nm in size were captured with a removal efficiency of ∼99.99%. Moreover, the conductive filters exhibited excellent performances in terms of the pressure drop (∼4.9 Pa at 10 cm s^–1), quality factor (∼2.2 Pa^–1 at 10 cm s^–1), and dust holding capacity (12.5 μg mm^–2). After being cleaned by water, the filtration efficiency and pressure drop of the conductive filter was perfectly recovered, which indicates its good recyclability. It is expected that these promising features make the conductive fibrous filter have a great potential for use in low-cost and energy-efficient air cleaning devices as well as other relevant research areas

Highly Stretchable, Hysteresis-Free Ionic Liquid-Based Strain Sensor for Precise Human Motion Monitoring

A highly stretchable, low-cost strain sensor was successfully prepared using an extremely cost-effective ionic liquid of ethylene glycol/sodium chloride. The hysteresis performance of the ionic-liquid-based sensor was able to be improved by introducing a wavy-shaped fluidic channel diminishing the hysteresis by the viscoelastic relaxation of elastomers. From the simulations on visco-hyperelastic behavior of the elastomeric channel, we demonstrated that the wavy structure can offer lower energy dissipation compared to a flat structure under a given deformation. The resistance response of the ionic-liquid-based wavy (ILBW) sensor was fairly deterministic with no hysteresis, and it was well-matched to the theoretically estimated curves. The ILBW sensors exhibited a low degree of hysteresis (0.15% at 250%), low overshoot (1.7% at 150% strain), and outstanding durability (3000 cycles at 300% strain). The ILBW sensor has excellent potential for use in precise and quantitative strain detections in various areas, such as human motion monitoring, healthcare, virtual reality, and smart clothes