Molecular Diodes: Irreversible Motion in Nanofabricated Arrays Forward This work sprung from my collaboration with Prof. Jim Sturm and his students

This work sprung from my collaboration with Prof. Jim Sturm and his students Richard Huang, David Inglis and John Davis. Richard Huang came up with a brilliant and simple scheme by which a offset array of posts could deterministically separate in a binary manner large objects from small objects with extraordinary precision in a low Reynold number flow. The underlying idea behind this “bump” array is what a physicist grandly calls broken symmetry: the offset row of posts makes bundles of streamlines jitter back and forth, larger objects sample more than one streamline bundle and are deflected along the clear-axis of the offset array. A straightforward application of the original idea down in size to objects well below a micron is fraught with difficulties because diffusion contravenes the deterministic physics of the bump array, without further new ideas the only way to separate at smaller sizes is to run the flow faster, and at the size of proteins high resolution separation occurs at flow speeds of 1 m/sec and pressure gradients of hundreds of bar/cm: in principle doable but not so interesting.