Electrowetting-based Actuation of Model Biological Fluids
Niyusha Samadi, Ph.D.
Concordia University, 2016
In the past two decades, microfluidics-based lab-on-a-chip devices have received growing interest, and researchers have been developing chemical and biological analysis systems on very small scales. In Lab-on-a-chip systems, the goal is reducing chemical laboratory procedures and using miniaturized rapid, portable, inexpensive and reliable equipment which can be applied in medical diagnostics, and basic scientific research. The driving force behind the Lab-on-a-chip concept is “microfluidics” where contrary to bulk flows; surface tension is a dominant force for liquid handling and actuation. One method of actuation involves applying an external electric field which changes the surface tension between the solid-liquid interface reducing the meniscus contact angle and inducing motion of a droplet in a microchannel. This phenomenon is called “electrowetting”.
In this research, the effect of electrowetting on the behavior of biopolymer solutions such as DNA is experimentally investigated. To better assess the electrowetting phenomenon of such complex solutions, the physics of electrowetting of aqueous biopolymer solutions should be completely understood. Such a fundamental understanding currently does not exist. For this purpose, the effect of fluid composition (i.e. different concentrations of DNA solutions and the type of buffer solution) on the static response of the droplet to electric field variables such as applied voltage is identified.
In the transient response, the time and voltage dependency of the parameters such as droplet speed, total displacement, and elongation of the droplets of distilled water, Tris-HCl buffer and the DNA solutions is studied. Among these parameters, the droplet speed is a key factor which controls the rate of microfluidics-based lab-on-a-chip devices. It is found that the negatively charged oxygen ions on the DNA chain will affect the dynamic behaviour of DNA solutions significantly, and the electrophoretic velocity increases with voltage. Besides, it appears that the higher the DNA concentration is, the higher the DNA droplet velocity will be; as the ionic strength and the total effective charge increase with DNA concentration. Therefore, both electrowetting and electrophoretic forces contribute to the movement of the negatively charged droplets of DNA solutions.
Overall, the results of this study will help us to better understand, analyze, design and prototype the microfluidic-based systems for DNA solutions.