Experimental investigation of the possibility of transporting a droplet over a hydrophilic spot in digital microfluidics

E. Samiei, M. Hoorfar
University of British Columbia, CA

Keywords: digital microfluidics, hydrophilic spot, droplet transport


This paper studies the transport of a water droplet over a hydrophilic spot (representing the sensing surface of a biosensor) created on the top plate of a digital microfluidic chip. For this purpose, a closed DMF system with an array of electrodes has been designed, and the hydrophilic spot created on the top plate was placed above one of the middle actuating electrodes. The hydrophilic spots were created on the top plate by removing Teflon from desired locations using the lift-off process. A series of experiments were conducted for different electrode sizes, droplet sizes, gap sizes between top and bottom plates, and hydrophilic spot sizes and locations (i.e., the center and two ends of the electrode). The results obtained for different hydrophilic spot sizes show that there is a threshold for the surface area of the spot above which the motion of the droplet is hindered by the hydrophilic spot. Increasing the electrode size and hence the droplet size the threshold for the hydrophilic surface area increases, while droplet becomes less stable and splits over the hydrophilic spot. Also, increasing the gap size increases threshold for spot surface area and makes the droplet more stable, preventing its break up.