A prototype personal aerosol sampler based on electrostatic precipitation and electrowetting-on-dielectric actuation of droplets

Abstract

This is an Open Access article, distributed under the terms of the Open Government Licence. http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/ Crown Copyright ?? 2016. Published by Elsevier Ltd. All rights reserved. The version of record (T. G. 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, pp. 43-53, May 2016) is available online at doi: https://doi.org/10.1016/j.jaerosci.2016.01.007.An electrostatic precipitator (ESP) based personal sampler with a laboratory based electrowetting-on-dielectric (EWOD) concentrator could provide a high concentration rate personal aerosol sampler system. A prototype system has been developed based on the concept of a lightweight personal ESP collecting aerosol particles onto a hydrophobic surface followed by the use of an EWOD actuated droplet system to transfer the deposited sample into a microlitre size water droplet.A personal sampler system could provide military or civilian personnel with a wide area biological monitoring capability supplying information on who has been infected, what they have been infected with, how much material they were exposed to and possibly where and when they were infected. Current commercial-off-the-shelf (COTS) personal sampler solutions can be bulky and use volumes of water to extract the sample that are typically a thousand times greater than the proposed method.Testing of the prototype ESP at a sample flow rate of 5Lmin-1 demonstrated collection efficiencies greater than 80% for sodium fluorescein particles larger than 4??m diameter and of approximately 50% at 1.5??m. The ESP-EWOD system collection efficiency measured for Bacillus atrophaeus (BG) spores with an air sample flow rate of 20L min-1 was 2.7% with a concentration rate of 1.9??105 min-1. This was lower than expected due to the corona ions from the ESP affecting the hydrophobicity of the collection surface and hence the EWOD efficiency. However, even with this low efficiency the concentration rate is more than an order of magnitude higher than the theoretical maximum of the best current COTS personal sampler. For an optimised system, ESP-EWOD system efficiency should be higher than 32% with a comparable increase in concentration rate

Real-time sensing of bioaerosols: Review and current perspectives

“…Microfluidic devices aimed at bioaerosol detection have recently been developed (Choi et al 2017;Novosselov et al 2014), usually consisting of a collector, delivering bioaerosols into microfluidic liquid volumes, integrated with a biological assay. Aerosol is collected via impaction into microdroplets, directing aerosols into winding microchannels of a chip, or depositing aerosols onto a small substrate for later recovery (Foat et al 2016;Han, An, and Mainelis 2010). After collection, a variety of assays may be applied including ATP measurement, PCR, immunoassay, or genomic sequencing (Mairhofer, Roppert, and Ertl 2009).…”

Fully integrated digital microfluidics platform for automated immunoassay; A versatile tool for rapid, specific detection of a wide range of pathogens

“…Hence, it is essential to maximise the concentration of the sample resulting from the collection stage of the bio-detection chain. We propose that our detection technique should be used in conjunction with a DMF-based air sampler, such as that presented by Foat et al (2016), which produces highly concentrated droplet samples. Such a sampling technique relies on continuous sampling over a period of time prior to a concentration step using EWOD based DMF to transfer the material into a liquid droplet.…”

“…In the last ten years, electrowetting-on-dielectric (EWOD) based digital microfluidics (DMF) (Abdelgawad and Wheeler 2009;Jebrail et al 2012;Mugele and Baret 2005;Nelson and Kim 2012;Pollack et al 2000), used in conjunction with various air-sampling techniques, has been envisioned as a powerful tool to produce in-droplet highly concentrated sample from airborne collected material (Jönsson-Niedziółka et al 2011;Zhao and Cho 2006;Zhao et al 2008). More recently, a personal air sampler using EWOD based DMF as a way to increase the sampling concentration rate has been demonstrated (Foat et al 2016). This technique produces highly concentrated droplet samples that can be transferred into a bespoke bio-detector.…”

“…To take full advantage of the highly concentrated small volume samples resulting from the collection process, it is desirable to use them undiluted in their microlitre-droplets form. EWOD based DMF appears very well suited: in addition to an obviously very straight-forward integration with other EWOD based systems such as the one presented by Foat et al (2016), DMF carries the promise of a possible paradigm shift in micro-volume bioassays by allowing complex manipulation of discrete microlitre-scale droplets (Abdelgawad and Wheeler 2009). In the last decade, a number of these systems have been developed to serve as a platform for DNA or antibody based assays using magnetic particles as solid support for the separation of target material (Kokalj et al 2015).…”

Droplet-based microfluidics detector for bioaerosol detection

“…In designing a system, concentration rate should be optimized by increasing the air flow rate and collection efficiency, or decreasing the volume of capture liquid preferably to microfluidic volumes, because this improves the aerosol detection sensitivity. Past studies reconciling microfluidics with aerosol collection (by deposition of aerosol in channels/half-channels) have reported concentration rates of 10 4 -10 6 min ¡1 , and have delineated the limitations with these approaches (Han and Mainelis 2008;Han et al 2010Han et al , 2011Jing et al 2013Jing et al , 2014Pardon et al 2015;Han et al 2015a,b;Foat et al 2016;Ma et al 2016). These studies have shown successes, but require further work in integration with assay platforms, clearly demonstrating end-to-end bioaerosol collection and identification, estimating limits of detection, and detailed field testing.…”