Quantification of Airborne Endotoxins

Fine (aerodynamic diameter $\le$ 2.5 μm, PM2.5) and coarse particles (aerodynamic diameter $\ge$ 2.5 μm) were collected on glass filters (Advantec Co., Ltd., Tokyo, Japan) and quartz filters (Pall Life Sciences, Port Washington, NY, USA), respectively, in the city of Sasebo (129.79 °E, 33.10 °N) using a high volume air sampler (HV1000R, Shibata Scientific Technology, Soka, Japan) equipped with an impactor (Shibata Scientific Technology) at a flow rate of 1 m³/min for 1 week per filter. The quartz and glass filters were preheated to 250 °C for 2 h before sampling for the estimation of endotoxin level. Following sample collection, the filters were stored at −80 °C until the preparation of sample solutions.
To quantify endotoxins in fine and coarse particles, 15 % of sample filter (corresponding to 1512 m³ of air) was extracted with endotoxin-free water containing 0.025 % Tween-20 using an ultrasonic apparatus for 30 min, as previously described [22 (link),23 (link)]. The extract was centrifuged, and a portion of the supernatant was used for endotoxin analyses. A sample solution for luciferase reporter assay was extracted with distilled water from 15 % of the sample filter through ultra-sonication for 30 min, followed by centrifugation. The supernatant was lyophilized to obtain powder and resolved with culture medium before use in the luciferase reporter assay.