Continuous and real-time bioaerosol monitoring by combined aerosol-to-hydrosol sampling and ATP bioluminescence assay.

ABSTRACT

We present a methodology for continuous and real-time bioaerosol monitoring wherein an aerosol-to-hydrosol sampler is integrated with a bioluminescence detector. Laboratory test was conducted by supplying an air flow with entrained test bacteria (Staphylococcus epidermidis) to the inlet of the sampler. High voltage was applied between the discharge electrode and the ground electrode of the sampler to generate air ions by corona discharge. The bacterial aerosols were charged by the air ions and sampled in a flowing liquid containing both a cell lysis buffer and adenosine triphosphate (ATP) bioluminescence reagents. While the liquid was delivered to the bioluminescence detector, sampled bacteria were dissolved by the cell lysis buffer and ATP was extracted. The ATP was reacted with the ATP bioluminescence reagents, causing light to be emitted. When the concentration of bacteria in the aerosols was varied, the ATP bioluminescence signal in relative light units (RLUs) closely tracked the concentration in particles per unit air volume (# cm-3), as measured by an aerosol particle sizer. The total response time required for aerosol sampling and ATP bioluminescence detection increased from 30 s to 2 min for decreasing liquid sampling flow rate from 800 to 200 µLPM, respectively. However, lower concentration of S. epidermidis aerosols was able to be detected with lower liquid sampling flow rate (1 RLU corresponded to 6.5 # cm-3 of S. epidermidis aerosols at 200 µLPM and 25.5 # cm-3 at 800 µLPM). After obtaining all data sets of concentration of S. epidermidis aerosols and concentration of S. epidermidis particles collected in the flowing liquid, it was found that with our bioluminescence detector, 1 RLU corresponded to 1.8 × 105 (±0.2 × 105) # mL-1 of S. epidermidis in liquid. After the lab-test with S. epidermidis, our bioaerosol monitoring device was located in the lobby of a building. Air sampling was conducted continuously for 90 min (air flow rate of 8 LPM, liquid flow rate of 200 µLPM) and the ATP bioluminescence signal of indoor bioaerosols was displayed with time. Air sampling was also carried out using the 6th stage of Andersen impactor in which a nutrient agar plate was used for the impaction plate. The sample was cultured at 37 °C for five days for colony counting. As a result, it was found that the variation of the bioluminescence signal closely followed the variation of indoor bioaerosol concentration in colony forming unit (CFU) and 1 RLU corresponded to 1.66 CFU m-3 of indoor bioaerosols. Our method can be used as a trigger in biological air contamination alarm systems.