Study on the manipulation of droplets using an aqueous two-phase system in the microfluidic system

Abstract

Droplet-based microfluidics has the various potential applications in the chemical processes and biological analysis systems for microreaction, crystallization, screening, etc. In order to utilize the droplet-based microfluidic for the chemical or biological processes, the generation and the manipulation of the droplets must be developed. Previous studies have selected the oil/water system to form the dispersed droplets in microfluidic channel. In this study, the aqueous two-phase system (ATPS) which is made by dissolving tetrabutylammonium bromide (TBAB) and ammonium sulfate (AS) with deionized water is used in order to realize the droplet-based microfluidic system. AS-rich phase of ATPS shows the electrophoretic attraction to the positive electrode under electric field. This phenomenon can be applied to active generation and manipulation of the droplets. Firstly, the droplet sorting has been demonstrated in the microfluidic device. By applying the electric potential with pulsed signal, the electrophoretic force could successfully change the direction of the moving droplet into the branched channel. And the number of droplets which passed through the specific channel could be controlled when the duration of electric signal was adjusted. This method is expected to realize the automatic sorting of droplets if combined with detection system of color or florescence intensity. Secondly, the droplet merging, which is one of the important techniques to investigate the microreaction in droplet-based microfluidic device, has been demonstrated by electrohydrodynamic manner. From experimental results, the coalescence of droplets depends on the configuration which is the distance and angle between two droplets before the electric potential is applied along the channel. The successful droplet merging was occurred when the two droplets approached each other with the distance under $200 \microm$. And the synthesis of Prussian blue pigment was performed by the droplet mer...