Abstract: This invention comprises an apparatus and method for the manipulation of materials, including particles, cells, macromolecules, such as proteins, nucleic acids and other moieties, in fluid samples. The apparatus comprises an enclosed chamber on a chip having an internal microstructure with surface area substantially greater than the facial surface area of the internal structure. Generally the internal microstructure comprises a continuous network of channels, each of which has a depth substantially greater than its width. The network may comprise a single channel, a single channel with multiple branches, multiple channels, multiple channels with multiple branches, and any combination thereof. The internal structure may present an inert, non-reactive surface, or be coated with a reactive ligand, or be electrically conductive and optionally be coated with an electrical insulator. Discrete portions of the internal structure may differ in structural and surface properties.