Exactly what happens as the fragments move through the maze is difficult to measure because the pores vary randomly in size and shape. In order to do controlled studies, Harold Craighead, Cornell professor of applied and engineering physics, and graduate students Jongyoon Han and Stephen Turner have used the Cornell Nanofabrication Facility to make microscopically small sieves with openings of controlled sizes. Using the photolithography techniques originally created to make electronic devices on silicon chips, the researchers carved channels 30 microns wide with alternating deep and shallow sections. The deep sections are about 1 micron high. Frames from a video showing how DNA molecules move through a nanomanufactured channel and pass through narrow sections.
Light areas are the deeper sections of the channel.
The DNA chain, collapsed into a roughly spherical shape, comes up against the narrow opening. A portion of the chain extends into the narrow space. The rest of the chain unwinds and follows. The molecule moves across the next deep section, reforming into a sphere as it goes. DNA molecules in a water solution were introduced at one end of the channel, and an electric field was applied to pull them toward the other end.