On-chip manipulation of objects using mobile oscillating bubbles

This paper describes a new on-chip manipulation method for handling millimeter- and micron-sized objects using oscillating mobile bubbles. It is found that acoustically excited oscillating bubbles can attract and capture neighboring objects. A variety of objects, including hydrophilic glass beads (80 mu m), polystyrene beads (100 mu m), a fish egg (similar to 1 mm) and a live water flea (similar to 1 mm), are successfully captured. The capturing performance is characterized using 80 mu m hydrophilic glass particles while varying the acoustic excitation frequency and amplitude. The oscillation amplitude of the bubbles is quantified using high-speed images. At the natural frequencies of the bubbles the capturing range is highest. The capturing range increases as the oscillation amplitude increases. It is also found that while the bubbles are in lateral motion the capturing force is strong enough to hold the captured objects. By integrating acoustic excitation with electrowetting-on-dielectric (EWOD) bubble transportation, it is demonstrated that oscillating mobile bubbles can capture, carry and release neighboring objects on a chip. This new manipulation method may provide an efficient tool for handling millimeter- as well as micron-sized objects such as biological cells.