  In contrast to the commonly used spherical Janus particles, here we used
engineered Janus particles that are fabricated using photolithography technique
for precise control over their geometry and coated regions. Specifically, we
studied a lollipop-shaped complex particle where its head is coated with gold
while its tail is left bare. Due to their distinct electrical properties (i.e.
electrical polarizability) the particle exhibits force equilibrium where
opposite dielectrophoretic forces acting on its head and tail exactly cancel
each other to yield a stable equilibrium position. This was realized in a
quadrupolar electrode array where the equilibrium position of the engineered
particle could be tuned by the frequency. This stands in contrast to the
standard dielectrophoretic behavior where the particle shifts positions from
either the center of the quad to the very edge of the electrodes when shifting
from a negative to positive dielectrophoretic response, respectively. This
opens new opportunities for positioning control of such complex particles for
self-assembly, biosensing, biomimetic spermatozoa and more.
