Möbius strips are special loops that only have one continuous side. Now we've built the smallest Möbius strips ever - out of DNA. Here you can see the nanometer-sized DNA loops, folded like origami.
The ability to create complex structures on the tiniest of scales is one of the great challenges of nanotechnology. In particular, chemists are looking for particular topological structures, or structures that keep their basic properties no matter how much you stretch or twist them. A Möbius strip is a good example of such a structure, because no matter what you do it (short of tearing it, of course), it will always have only one side.
Earlier attempts at this sort of nanotechnology DNA folding have been termed DNA origami, but this is actually more accurately DNA kirigami, named for the Japanese art of cutting and folding paper. Here are a few more shots of the DNA Möbius strips above and below.