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Multidimensional And Multifunctional Manipulations Of Nanoliter/Picoliter Droplets By Combining Microfluidics With Magnetism

Posted on:2013-02-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:K ZhangFull Text:PDF
GTID:1118330371454993Subject:Analytical Chemistry
Abstract/Summary:PDF Full Text Request
Recently, droplet microfluidic chip has been rapidly developed for handling nanoliter/pico liter (10-9-10-12 L) liquids. It has many advantages including less consumption of samples and reagents, rapid mixing, without cross contamination and good repeatability. So far, a wide variety of applications have been achieved through this technique including chemistry and biology. For successful droplet-based applications, it is the premise and key to develop simple and high efficient droplet manipulation technique. Because microfluidic chip droplets have many essential characters including small volume, rapid flow and easy deformation, it often needs external forces to assist to manipulate them. In this thesis, methods of multidimensional and multifunctional manipulations of nanoliter/picoliter droplets are presented by combining microfluidics with magnetism. Compared with other methods, these techniques have many advantages including low price, simple fabrication, easy to operate, good compatibility and good repeatability.First, the microfluidic chip manipulation of picoliter superparamagnetic droplets using magnetic attraction is developed. Water ferrofluid flow is sheared into picoliter superparamagnetic droplets by silicon oil flow in a T-junction structure. Without an external magnetic field, superparamagnetic droplets flow along the laminar flow in the main-microchannel. With an external magnetic field, superparamagnetic droplets can be deflected from their original direction by magnetic attraction. Theoretical and experimental results demonstrate that the deflection is proportional to the magnetic field gradient and magnetic nanoparticle concentration. Superparamagnetic droplets can be precisely manipulated into the designated sub-microchannels by controlling effective magnetic field gradient range simply. Moreover, single superparamagnetic droplet can be sorted from nonmagnetic droplets first and then dispersed into the designated sub-microchannel.Second, the microfluidic chip manipulation of nonmagnetic droplets using magnetic repulsion is developed. Water flow is sheared into picoliter nonmagnetic water droplets by oil ferrofluid flow in a T-junction structure. Without an external magnetic field, droplets flow along the laminar flow in the main-microchannel. With an external magnetic field, droples can be deflected from their original flow direction by magnetic repulsion. In the comb-shaped and multiple outlets structures, multiple essential droplet operation units are successfully implemented by controlling magnetic field size and range such as droplet splitting, dispensing, oil-phase exchange, trapping, release and demulsification.Third, the microfluidic chip manipulation of nonmagnetic droplet by magnetic control of local oil-phase laminar flow is developed. Without an external magnetic field, ferrofluid and mineral oil can form stable laminar flow in the microchannel. With an external magnetic field, local ferrofluid is bumped by magnetic attraction. Flowing droplets can be immobilized at micropillary arrays by adjusting direction of local laminar flow and trapped into long sub-microchannels by changing resistance distribution of local laminar flow. In the whole process, droplets could be manipulated with or without contacting with ferrofluid. Immobilized and captured droplets facilitate the detection of droplet contents.Forth, the microfluidic chip comprehensive two-dimensional manipulation of nonmagnetic droplet is developed. Firstly, a simple and robust based on gravity pressure technique is presented to control droplet. In this method, picoliter/nanoliter droplets with controllable sizes and numbers are sampled from nanoliter samples/reagents with almost 100% efficience. Due to well compatibility in operation and sensitivity, motion of droplets can be precisely controlled in the±X direction and±Y direction by combining hydrostatic pressure and magnetic repulsion. As a demonstration, fluorescence intensity analysis base on multistep procedures is achieved.Fifth, the microfluidic chip three-dimensional manipulation of nonmagnetic droplet is developed. Water-drops and unshaped ferro-drops are naturally combined together under interface force between water-phase and oil-phase. As a result, water-drops can be motioned by magnetic attraction on an open two-dimensional and three-dimensional platform surfaces. Shaped ferro-drops are formed by fixing unshaped ferro-drops onto magnet surfaces. The shaped ferro-drops can absorb, transfer and completely desorb water-drops to surfaces of water-phase, oil-phase and solid-phase without any cross contamination. Two representative applications are demonstrated:implementing synchronized chemical reactions of ten pairs of water-drops containing different concentrations; encapsulating and stimulating embryonic stem cells into water-drops.
Keywords/Search Tags:microfluidics, nanoliter/picoliter droplet, magnetic attraction, magnetic repulsion, manipulation
PDF Full Text Request
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