A MEMS-based system and a method are described for separating a target particle from the remainder of a fluid stream. The system makes use of a unique, microfabricated movable structure formed on a substrate, which moves in a rotary fashion about one or more fixed points, which are all located on one side of the axis of motion. The movable structure is actuated by a separate force-generating apparatus, which is entirely separate from the movable structure formed on its substrate. This allows the movable structure to be entirely submerged in the sample fluid.