Abstract
Introduction: One of the main challenges facing in-field detection of harmful aerosol is the low concentration of target airborne material. Hence, generating concentrated samples (within small liquid volumes) is key to providing low limit-of-detection. In previous work, we have demonstrated a novel system combining an Electrostatic Precipitator (ESP) sampler with an Electrowetting-on-Dielectric (EWOD) elution device that generated samples with between a 33 to 1000 times greater concentration than from an SKC BioSampler [1]. However, testing[1] has also shown that the ESP-EWOD system can perform poorly when background aerosol concentrations are high. This work presents an overview of the development and characterisation of ruggedised and weather-proofed ESP and EWOD systems built for future field trials. In addition, the impact of Tween-80 surfactant in improving aerosol recovery in EWOD elution was examined.
Methodology: The handheld ESP [1] was redesigned to incorporate a commercial PM10 inlet and weatherproofing. The ESP housing has improved sealing to cope with the increased pressure drop from the PM10 inlet. The EWOD included larger electrodes, enabling them to cope better with high aerosol concentration on the collection surface and reduce complexity. Bacillus atrophaeus (BG) spores were aerosolised within a negative-pressure aerosol chamber to produce a 0.7 particle count/cm3 concentration. Three ESP devices were examined using a flow rate of 16.7 L/min for a collection time of 30 minutes. The spores collected on the ESP slides were imaged by an EVOS M7000 microscope and counted using image processing software. The EWOD device performs the elution of the samples with a 2.7 µl droplet with 0, 1.4E-4 and 1E-2 % of Tween-80 in deionised (DI) water. Flow cytometry analysis determined the absolute count of BG spores in the droplet sample.
Results: Microscopy revealed that the field trial ESP had a 49 % average aerosol collection efficiency, with a 20 % standard deviation from 17 results. The elution process removed, on average, 51 % of the spores on the collection surface, with no notable improvement when Tween-80 was introduced for the elution. Tween-80 also negatively impacted the EWOD droplet’s actuation performance with a lower completion rate of the elution process. The ESP-EWOD system produced an average concentration rate of 1.1E+5 /min, which is more than an order of magnitude greater than the theoretical maximum of the commercial-off-the-shelf personal samplers and on par with the previous generation ESP-EWOD system [2].
Conclusion: The field trial ESP and EWOD system retained BG spore concentration rate performance despite the ruggedisation of the devices. Introducing the Tween-80 surfactant in the elution process showed no improvement in BG spore removal and was detrimental to the EWOD droplet actuation. The ESP-EWOD devices were involved in a successful outdoor field trial after the conclusion of this study.
Reference list:
[1] N. Chan et al., "Test and evaluation of a new bioaerosol collector in a laboratory setting," 2023.
[2] T. Foat et al., "A prototype personal aerosol sampler based on electrostatic precipitation and electrowetting-on-dielectric actuation of droplets," Journal of Aerosol Science, vol. 95, 2016.
Methodology: The handheld ESP [1] was redesigned to incorporate a commercial PM10 inlet and weatherproofing. The ESP housing has improved sealing to cope with the increased pressure drop from the PM10 inlet. The EWOD included larger electrodes, enabling them to cope better with high aerosol concentration on the collection surface and reduce complexity. Bacillus atrophaeus (BG) spores were aerosolised within a negative-pressure aerosol chamber to produce a 0.7 particle count/cm3 concentration. Three ESP devices were examined using a flow rate of 16.7 L/min for a collection time of 30 minutes. The spores collected on the ESP slides were imaged by an EVOS M7000 microscope and counted using image processing software. The EWOD device performs the elution of the samples with a 2.7 µl droplet with 0, 1.4E-4 and 1E-2 % of Tween-80 in deionised (DI) water. Flow cytometry analysis determined the absolute count of BG spores in the droplet sample.
Results: Microscopy revealed that the field trial ESP had a 49 % average aerosol collection efficiency, with a 20 % standard deviation from 17 results. The elution process removed, on average, 51 % of the spores on the collection surface, with no notable improvement when Tween-80 was introduced for the elution. Tween-80 also negatively impacted the EWOD droplet’s actuation performance with a lower completion rate of the elution process. The ESP-EWOD system produced an average concentration rate of 1.1E+5 /min, which is more than an order of magnitude greater than the theoretical maximum of the commercial-off-the-shelf personal samplers and on par with the previous generation ESP-EWOD system [2].
Conclusion: The field trial ESP and EWOD system retained BG spore concentration rate performance despite the ruggedisation of the devices. Introducing the Tween-80 surfactant in the elution process showed no improvement in BG spore removal and was detrimental to the EWOD droplet actuation. The ESP-EWOD devices were involved in a successful outdoor field trial after the conclusion of this study.
Reference list:
[1] N. Chan et al., "Test and evaluation of a new bioaerosol collector in a laboratory setting," 2023.
[2] T. Foat et al., "A prototype personal aerosol sampler based on electrostatic precipitation and electrowetting-on-dielectric actuation of droplets," Journal of Aerosol Science, vol. 95, 2016.
| Original language | English |
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| Publication status | Published - 17 Mar 2025 |