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