미세유체기술을 이용한 기능성 콜로이드 입자의 합성 및 2차원 배향을 통한 바이오전자센서 응용연구

Abstract

Microdroplets in microfluidics offer a great number of opportunities in chemical and biological research. They provide a compartment in which species or reactions can be isolated, they are monodisperse and therefore suitable for quantitative studies, they offer the possibility to work with extremely small volumes, single cells, or single molecules, and are suitable for high-throughput experiments. This study introduces a robust microfluidic technique for fabrication of uniform, functional, elastomer, conducting, and anisotropic microparticles. By taking advantage of the coaxial flow-focusing of immiscible fluids, monodisperse emulsion drops are generated in capillary based microfluidic device. The consecutive photo-polymerization produces uniform microparticles. Basically, we observe how flows in the microchannel affect the size and uniformity of emulsion drops as well as the structure and chemistry of the resulting particles. We first introduce a facile and straightforward approach for the fabrication of uniform elastomer microcapsules with shells comprising a polyurethane thin elastomer membrane. Controlled adhesion of the inner and outer interfaces of the W/O/W double emulsion drops and consecutive polymerization of polyurethane precursors between the interfaces lead to the production of a mechanically resilient complex microshell. This study is expected to be applicable to a variety of encapsulation applications such as packaging and storage under harsh environments. We also report introduces a practically useful approach for fabrication of hydrogel microcapsules layered with a mechanically robust polyelectrolyte/silica thin shell. For this, monodisperse negatively charged hydrogel microparticles were fabricated combining the microfluidic technique and subsequent photo-polymerization. Then, alternate polyelectrolyte layers were generated onto the microparticles by using the layer-by-layer deposition. In the final stage, reduction of silicate on the polyelectrolyte layer was conducted to form silica layer on the outer most layer of the shell. Uniform covering of the periphery of the hydrogel microparticles with the hybrid shell layer was confirmed by SEM and EDX analyses as well as by improved structural shell resistance to osmolality. The thickness of the shell layer was detected by approximately one micrometer. Finally, we demonstrated that the polyelectrolyte/silica hybrid shell showed remarkably low permeability against small molecules, which allows us to explore microcapsule applications toward complete segregation and stabilization of water-soluble active molecules. Third, a robust and straightforward approach for fabrication of a new type of colloidal pressure sensors was proposed. For this purpose, we synthesized uniform conductive magnetic-patchy microparticles using a microfluidic technique and then coated them with poly (3,4-ethylene dioxythiophene)-poly (styrene sulfonate) layers using the layer-by-layer deposition. Finally we showed that the magnetic-patchy conductive microparticles could be positioned on the target sites while precisely detecting pressure changes with excellent sensitivity. Finally, we introduce a new platform technology for designated 2-dimensional colloidal arrays by using Janus microparticles. Janus microparticles are synthesized by polymerizing biphasic emulsion drops generated by adjusting the spreading coefficient between −4.4 and −7.2 mN/m. We demonstrate that unidirectional rubbing of Janus microparticles can lead to their exact positioning in the holes of a stencil substrate. We also show that the ratio of the hole diameter to the bigger bulb diameter of Janus particles, typically ranging from 1.05–1.16, is a critical factor that maximizes the particle positioning rate. Moreover, when the anisotropic geometry factor is near-zero, further enhanced positioning rate can be obtained owing to the increase in the structural hindrance against the hole dimension. Finally, we demonstrate that Janus microparticles with controlled size and shape anisotropy can be selectively arrayed at the desired hole sites of the stencil, thus enabling colloidal microprinting.