Electrophoresis of particles with the same charge does work so long as you do it
in a medium that affects the transport ability (i.e. a porous gel that lets
small particles migrate quickly, but slows down big ones, then you can get
separation based on size)...people do that to separate DNA.

try looking up "gel electrophoresis"

If you can't alter the medium in such a way though (which probably is the case
for a microfluidic device), then yes, dielectrophoresis is the way to go.

-Joe Grogan


Quoting Jesse D Fowler :

> If the particles have the same charge, electrophoresis will not work. You
> may have some luck with dielectrophoresis (DEP). Prof. Thomas B. Jones at
> the University of Rochester wrote a good book on Electromechanics of
> Particles with that very title. He has a web page at:
>
> http://www.ece.rochester.edu/users/jones/