At the top of this drawing are two double crossover molecules, A and B*, which are shown schematically. The complementarity between their sticky ends is represented as geometric complementarity. The * indicates that the B molecules contain DNA hairpins that project out of the plane of the helices; these hairpins act as topographic markers in atomic force microscopy (AFM). The two molecules are approximately 4 nanometers wide, 16 nanometers long and two nanometers thick. When these two tiles are mixed in solution, they form hydrgen bonded 2-D arrays that are several microns long, and hundreds of nanometers wide. The rows of projecting hairpins appear as stripes when visualized by AFM. The stripes are separated by about 32 nanometers, as expected.
To demonstrate the versatility of pattern formation on this scale by our system, and also to check the previous result, we have designed and assembled a second array, which is shown below.
Here, we have used four tiles, A, B, C and D* to tile the plane. The tiles are the same size as in the previous example, but now only one tile in four contains the protruding hairpins. These arrays are as well behaved as the previous ones, and form similar sheets in solution. However, now we expect the separation of the stripes to be about 64 nanometers, rather than 32 nanometers. Indeed, this is what is seen when these sheets are examined by AFM.
Thus, we can create specific structural features on the nanometer scale by self-assembly of double crossover arrays.
Return to Two Dimensional Arrays
Return to Ned Seeman's Nanotechnology Page
Return to Homepage for Ned Seeman's Lab