Concentration and binary separation of micro particles for droplet-based digital microfluidics

Abstract

This paper describes a concept of concentration and binary separation of particles and its experimental confirmations for digital microfluidics where droplets are driven by the mechanism of electrowetting-on-dielectric (EWOD). As a fundamental separation unit, a binary separation scheme is developed, separating two different types of particles in one droplet into two droplets, one type each. The separation scheme consists of three distinctive steps, each with their own challenges: (1) isolate two different types of particles by electrophoresis into two regions inside a mother droplet, (2) physically split the mother droplet into two daughter droplets by EWOD actuation so that each type of particle is concentrated in each daughter droplet, and (3) free the daughter droplets from the separation site by EWOD to ready them for follow-up microfluidic operations. By applying a similar procedure to a droplet containing only one type of particle, two daughter droplets of different particle concentrations can be created. Using negatively charged carboxylate modified latex (CML) particles, 83% of the total particles are concentrated in a daughter droplet. Successful binary separation is also demonstrated using negatively charged CML particles and no-charge-treated polystyrene particles. Despite the undesired vortex developed inside the mother droplet, about 70% of the total CML particles are concentrated in one daughter droplet while about 70% of the total polystyrene particles are concentrated in the other daughter droplet.

In-droplet preconcentration of microparticles using surface acoustic waves

“…Cho et al (11) 은 전기적 극성의 입자와 극성이 낮은 입자를 전기영동으로 구분하였으며, Brouzes et al (Fig. 4(a)) 액적 내부의 폴리스타이렌 입자는 나눠진 두 액적 모두에서 퍼 지게 된다.…”

Electrowetting on dielectric driven droplet resonance and mixing enhancement in parallel-plate configuration

“…Fundamentals of EWOD, including basic operations on a droplet, 2-4 dynamics of contact angle variation, 5,6 and contact angle saturation 7,8 have been extensively studied. Integrated functional chips 9-11 and in-droplet particle manipulation 12,13 based on EWOD have also been demonstrated. For applications using EWOD, especially in chemical and biochemical fields, efficient mixing of samples and reagents is always desired and is still an issue.…”

Hybrid opto-electric manipulation in microfluidics—opportunities and challenges

“…This simultaneous need for control of droplet movement and manipulation of particulate phases inside droplets can be very challenging. Though limited progress has been achieved in this direction, 92,[105][106][107] hybrid tools with their higher degrees of freedom offer significant opportunities in this direction. For example Shah et al 107 demonstrated target separation and individual manipulation of HeLa cell samples by using a combination of EWOD and OET ( Fig.…”