Microfluidic Droplet Manipulations And Their Applications In Chemistry And Biology

Microfliudics is a technology concerning appointed manipulations of very little liquid(ranging from 10-9 to 10-18 L)based on specific micro-/nano-structures as well as unique physical/chemical methods,and it helps to realize the detection,analysis and manipulations of certain chemical/biological phenomenons/processes on micro or nano scales.Microfluidics can achieve integration,automation and miniaturization of various assays in a microchip.Also,the manipulations of fluid inside microchannels provide new techniques as well as insights for chemical and biologial researches.Together with the development of new materials,micro-fabrication techniques,chemical modification methods and detection strategies,microfluidics has been applied in broad fields such as chemistry,biology,clinical medicine,pharmaceutics etc.Among the various branches of microfluidics,droplet microfluidics has become an important platform for analytical chemistry,cell biology,pharmaceutics and corresponding multi-discipline researches due to its advantages of high volume-surface ratio,high throughput,no cross-contamination and versatile manipulations.Utilizing the specific micro-structures as well as thermo,acoustic,optic or electric techniques,droplet generation,mixing,fission,fusion and sorting based on two immiscible liquids can be realized.Nowadays,droplet microfluidics has been widely adopted in fields of material synthesis,protein crystallization,particle generation,mass analysis,drug screening and single cell researches etc.In this thesis,droplet manipulations and their applications in chemical and biological researches have been investigated.We improved traditional hydrodynamic,pneumatic valve-based and electric droplet manipulations,which helped to achieve better performance of controlling the size,morphology,movement,arrangements and content concentration of droplets.Also,these advanced microdevices were used for mass analysis,single cell researches and micro-particle synthesis.The main work of this thesis is as following:1.We fabricated a microfluidic chip containing a Y-channel as well as a flow-focusing orifice.Through adjusting the flow ratio of liquid phases,Janus droplets could be generated and they could form different arrangements in the downstream channels.We also analyzed the generation and arrangement transition of this phenomenon theoretically.2.We integrated two flow-focusing orifices in a chip to generate two different kinds of droplet simultaneously,and then these droplets could fuse in the downstream channel to react in a controllable manner.At first,we used this chip to generate cell-laden disk-like calcium alginate hydrogel beads,which helped to realize cell immunofluorescent staining and monitoring.And this droplet system was also used for high-sensitive detection of Hg+ ions in water with help of gold nanoparticles.3.We improved traditional soft-lithography to fabricate a shape-controllable pneumatic 3D valve "nozzle" inside a three-layer microflidic chip.This nozzle could control the morphology of corresponding channels in both vertical and horizontal dimensions,thus raising the regulation ability and response for droplet size and content concentration.Also,we could synthesize core-shell microparticles using the same device.4.We integrated two flow-focusing structures and corresponding pneumatic valves to generate cell-laden hydrogel beads as well as to controllablly immobilize and release them on-chip.This system could be used for on-chip in situ cell viability tests.5.We fabricated 3D electrodes in the microfluidic chips through simply injecting conductive silva paste into the micro-chambers.These 3D electrodes showed better performance in droplet manipulations and had better biocompatibility compared to conventional 2D electrodes,which was confirmed theoratically and experimentally.Also,we realized converse charging process of different droplets in the same microchip.And this method was used for cell sorting.