Droplets generation and sampling on demand with peristaltic pumping systems

Abstract

In the last few decades, droplet microfluidics has been developed as a new area of microfluidics, where samples are compartmentalised in another immiscible phase. With these micro-droplets, Taylor dispersion can be minimised between samples and thorough mixing is easy and fast within the droplets themselves. Moreover, the sample consumptions are comparatively low as the samples are limited within nano-litre, pico-litre or even smaller droplets. Due to these attractive features, droplet microfluidics has been widely used as a platform to study various phenomena in chemistry, biology and physics. Droplets are normally generated in a T-junction or flow-focusing with syringe pumps or other pressure sources. An alternative way to generate droplets is to sequentially aspirate aqueous samples and carrier oil under negative pressures. Both of the typical T-junction methods and the current aspiration methods, have limitations in freely introducing/collecting samples into designed droplets, such as continuous sampling where introduction of samples does not affect the droplet generation, and in-situ sampling where samples from environment can be directly introduced into droplets. This ‘sample in’ problem is still a challenge in droplet microfluidics.

This thesis addresses the two droplets sampling issues in droplet microfluidics: continuous droplet sampling, and in-situ droplet sampling. To solve the first issue, a novel microfluidic platform was engineered which includes aspiration droplet generators, a peristaltic pumping system and a feedback system which is used to synchronise droplet generation with pulsations of flowrates from the peristaltic pump. The demonstration of this platform successfully shows the capability of continuously generating and pumping droplets. To solve the second issue, a micro peristaltic pump was engineered to realise a robust droplet generation method and a direct sample introduction from ‘out-world’ to chip. The results show that this device is capable of generating droplets in-situ.

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