Selective Wettability Assisted Nanoliter Sample Generation via Electrowetting-Based Transportation

A novel method for nanoliter sample generation is demonstrated. In this method, an electrowetting-based platform (EWOD) was used to transport a water droplet which was sandwiched between two hydrophobic plates, and the transportation was carried out by the direct electrical control of planar electrodes on the bottom glass substrate. In contrast to the air environment in ordinary EWOD, silicone oil was employed to surround the water droplet to reduce the surface hysteresis; therefore, the fluidic operations including cutting and transportation became easier to manipulate. While the droplet was moving through the electrodes, a nanoliter sample was produced within the circular hydrophilic area which was patterned on the upper ITO coated plate. Hence, based on the definition of selective wettability areas, the sample volume is capable to be well generated and controlled. Besides, in order to optimize the dimensions of electrode, the dimensional criterion for complete sample generation was investigated. The result shows that larger electrode width permits more flexibility to determine the radius of hydrophilic circle. Upon this mechanism, the hydrophilic circle of 0.25 mm diameter is able to generate the tiny sample of 3.9 nanoliter. Since the dimensions of the hydrophilic circle could be easily patterned in tens microns, this method has the potential to achieve the picoliter sample via similar procedure. Consequently, according to the tiny sample generation and reduction of hysteresis, such method is well-suitable for the versatile applications.