| dc.description |
Dielectrophoresis (DEP) is a separation method in which a non-uniform electric
field is used to induce a dipole moment in a suspended particle. If the polarization
of the particle is greater than that of the suspending medium, the particle will move
towards the region of higher field strength (positive DEP); while if the particle is
polarized less than the suspending medium, the particle will be moved towards the
low potential area (negative DEP). In recent years DEP has been gaining
popularity through the construction of microscale devices, and this is due largely
to the decrease in electrode spacing which allows for higher effective field
strengths.
Presented is the design, fabrication, and evaluation of a novel dielectrophoretic
based ratchet device. The electrodes required to produce the asymmetrical field
were constructed of electroformed nickel features grown on the surface of a resist
patterned seedlayer coated glass slide, and this is the first time electroforming has
been used to produce electrodes in the field of DEP. The electrodes were then
made stand alone features located on the glass slide by wet etch removal of the
unplated portions of the seedlayers located on the surface of the glass substrate.
The fluidic component of this device was constructed using replica molding of
poly(dimethylsiloxane), which contained a fluidic reservoir located over the
ratchet electrode features.
Particle selection was conducted using an a priori approach for particles of known
dielectric properties. The frequency responses of perspective test particles to an
asymmetrical electric field were determined through calculation of the real
component of the Clausius-Mossotti factor (Re[K(ω)]). From these calculations,
magnetite and polystyrene spheres were selected as test particles. The device was
then evaluated using the test particles selected to determine if particle collection
occurred in the regions dictated by Re[K(ω)]. Suspensions consisting of single
particle types and a mixture were then evaluated, and it was found that the
particles collected in the regions specified by the theoretical calculations. These
results showed that the device is capable of collecting particles based on the
dielectric properties of the magnetite particles and polystyrene spheres. |
|