  Gold-platinum catalytic pumps immersed in a chemical fuel are used to
manipulate silica colloids. The manipulation relies on the electric field and
the fluid flow generated by the pump. Catalytic pumps perform various tasks,
such as the repulsion of colloids, the attraction of colloids, and the guided
crystallization of colloids. We demonstrate that catalytic pumps can execute
these tasks sequentially over time. Switching from one task to the next is
related to the local change of the proton concentration, which modifies the
colloid zeta potential and consequently the electric force acting on the
colloids.
