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Particle manipulation with capillary flow and evaporation
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posted on 10.01.2017by Shao, Fenfen
Particle manipulation technologies are being updated with higher degree of sensitivity, efficiency and greater affordability. This research aims to investigate the use of capillary flow and evaporation for manipulating particles as this application has the characteristics of low cost and high quality of controllability, precision and delicateness. In particular, the research is focused on gaining knowledge of the factors that affect particle deposition behavior, establishing schemes for manipulating particles, as well as exploring the applications of using capillary flow and evaporation. Two main areas covered in this research are manipulating particles both in coverslip fluidics systems and droplet evaporation systems.
To manipulate particles in coverslip fluidics systems, a hydrodynamic capillary force scheme was developed. This method permits particles to be assembled and harvested while remaining hydrated in batches using a single setup. In addition, using this scheme, assembly of different sizes and types is possible. A directional flow control scheme was also developed to observe samples undergoing controlled fluid flow under the microscope, which is important for studying biochemical processes and motion dynamics. This scheme was successfully used in motion dynamic studies of Dunaliella algae swimming under fluid flow.
To manipulate particles in droplet evaporation systems, the particle deposition mechanism in an evaporating droplet for self-assembly was firstly exploited. Experiments were conducted to examine pattern differentiations between micron sized copolymer particles and silica particles, and it was found out that the basic deposition mechanism can be strongly influenced by a balance between capillary forces and drag arising from flow patterns in the droplet and interparticle capillary forces. Using this mechanism, it was then demonstrated that the evaporation process can be effectively controlled and optimized by adding simple interventions into the natural evaporation process resulting in two biomedical applications: functional biosensors and flagella construction. This intervention was further investigated and raised the awareness of studying the capillary flow (or wicking) generated by a porous medium and liquid bridges. Relevant experiments were performed on evaporative particle self-assembly influenced by capillary evacuation. In addition, electrical circuits from capillary flow driven evaporation deposition of carbon nanotube ink in non-porous V-grooves were created. This advances the manufacture of novel inexpensive microfluidic electrochemical based devices. Furthermore, a system of particle aggregation and harvest was constructed by using electroosmosis, superhydrophobic surfaces, capillary flow and evaporation. In this system, the wetting phenomenon was effectively hindered on superhydrophobic surfaces. To achieve the preconcentration of fluorescent protein samples without needing any energy sources while at the same time facilitating mixing, a droplet creation and retraction approach in capillary based microplates was successfully integrated into a droplet evaporation scheme, which is important in biochemical analysis. Based on this method, an improved method was then demonstrated to effectively achieve the preconcentration of fluorescent analytes by using superhydrophobic surfaces. This method is simple and robust and can be used to work with capillary wells which have shown to have significant advantage over standard microplate wells.
The outcomes of this research contribute significantly to the research field of particle manipulation, and provide enabling technologies for the future development and applications.