(A) Schematic of the NIST-Cornell nanofluidic device with complex 3-D surfaces. Each step of the staircase seen on the side marks a different depth within the chamber. The letter E shows the direction of the electric field used to move the nanoparticles through the device. The green balls are spheres with diameters of 100 nanometers whose size restricts them from moving into the shallower regions of the chamber. The coil in the deep end of the chamber (upper right corner) is a single DNA strand that elongates (upper left corner) in the shallow end. (B) Photomicrograph showing fluorescently tagged spherical nanoparticles stopped at the 100-nanometer level of the chamber, the depth that corresponds to their diameter. (C) Photomicrograph of a single DNA strand that is coiled in the deep end of chamber (box at far right) and elongated in the shallow end (box at far left). Larger boxes are closeups showing the fluorescently tagged strands.