Water-Injection Based BioCascade Impactor for Size-Fractionated Bioaerosol Collection

MOHAMMAD WASHEEM, Amin Shirkhani, Sudheer Salana, Yu-Ju Chen, Luis Angel Nino Barreat, Bright Amponsem, Amir Sharafudin, Sripriya Nannu Shankar, Arantzazu Eiguren-Fernandez, John Lednicky, Chang-Yu Wu, University of Miami

     Abstract Number: 273
     Working Group: Bioaerosols

Abstract
The BioCascade Impactor (BC) is a novel air sampling device that collects size-fractionated bioaerosols into three distinct size bins (>10, 4.1–10, 1.5–4.1 µm) through gentle liquid impaction. However, under low relative humidity conditions (<40% RH), the collection medium experiences high evaporation rates that lead to concentrating medium (other than water) and potential viability loss. This limitation is particularly concerning in occupational exposure monitoring, which requires prolonged sampling durations (≥3 hours). To address liquid loss and viability challenges, we developed jBioCascade, an upgraded BioCascade model incorporating a water injection system that stabilizes collection medium volume to prevent concentration fluctuations. This controlled liquid system injects sterile water at a user set interval and constant volume into sample collection dish to counteract evaporation. Experiments were conducted to evaluate liquid evaporation rates and viability conservation of Bacteriophage MS2 under varying humidity conditions. BioCascade was tested at 50%, 70%, and 90% RH in a controlled chamber and at 40% RH for ambient sampling, using 2 mL of 0.1X Phosphate buffer saline (PBS) as starting volume. The jBioCascade was also tested at 40% RH to determine water injection rates needed to stabilize PBS and virus transport medium (VTM). MS2 viability was assessed via plaque assays, and the results were analyzed using Two-Factor ANOVA. Viability conservation remained significantly high at 70% RH (p < 0.05) as compared to other RHs and was statistically similar at 50% and 90% RH (p > 0.05). Evaporation rate increased as RH decreased, with losses of 11 µL/min for PBS and 13 µL/min for VTM at 40% RH. The injection system was shown the capability to counteract this loss and can potentially be used for long-duration airborne pathogen sampling in fluctuating humidity conditions. Future deployments in occupational environments will validate its effectiveness in epidemiological surveillance and occupational assessment.