Poster Y13 - Towards quantitative assays in low-resource-settings with a low-cost, robust, fast, and equipment-free partitioning platform made of thermoplastic

Introduction: Deploying microfluidic devices for quantitative assays in low-resource settings requires a robust and cost-effective solution. Digital assays are ideal because they provide absolute quantification and use endpoint assays. The array of chamber format is appealing because it offers a fixed pattern for easier readout. The main challenge of this format is to efficiently prime thousands of chambers by displacing the air trapped in the nanoliter cavities. Most approaches use PDMS, which allows blind-filling. PDMS remains expensive to manufacture and is not suited for large-scale production. In contrast, thermoplastics are the materials of choice for manufacturing; however, they are not gas permeant at reasonable pressures. We solved this conundrum by designing chambers that harness capillary valving to ensure robust and rapid filling of large arrays of nanoliter chambers. Our device is unique because it can be translated into applications for low-resource settings due to its material, partitioning speed, robustness, and low equipment requirement.

Materials and

Methods: We fabricated the device by embossing a 1 mm thermoplastic cyclo olefin copolymer (COC) with a 5:1 wt. PDMS (Sylgard 184, Dow Corning) die. We sealed the device with a pressure-sensitive adhesive (PSA) film. We injected fluids with pressure controllers using newly developed magnetic connectors (Fig. 4), or with a manual 1,000 uL micropipette.

Results, Conclusions, and Discussions: Our thermoplastic partitioning platform harnesses capillary effects to control the progression of the liquid-air interface and ensures air displacement by providing an escape route for the air (Fig. 1). We tested a device of 3,200 chambers for its robustness against injection pressure, filling and partition rate, and droplet volume.
Theoretically, capillary valving is valid only at a low Capillary number. Still, we were able to fill the entire array at a high filling success rate up to our highest injection pressure tested (24 psi) (Fig. 2a). Surprisingly, injection with a 1,000 uL pipette (estimated at 4.5 psi) yielded near-perfect filling rates (99.8%) (Fig. 2b).
Partitioning with surfactant fluorinated oil using the manual pipette showed an excellent success rate of over 99.4% (Fig. 3). Remarkably, the volume distribution of partitions is exceptionally tight, with a standard deviation of 3% or less, like droplet microfluidics.
The filling and partitioning steps take less than 20 seconds to perform.
Conclusion and perspective
Our partitioning device exhibits exceptional performance in terms of robustness, partitioning success rate, and partition volume distribution. We are currently increasing its chamber density and making all-COC devices to perform molecular assays.

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