One of the first things that you learn in molecular biology is how the structure of DNA is a double helix. We've known this for a long time, but just through doing clever science, not because anyone had ever seen a DNA molecule before. For the first time, scientists at the University of Genoa have taken a picture of DNA, and happily it really is a double helix.
The structure of DNA was first worked out back in the 1950s using a technique called X-ray diffraction. X-rays are fired at a crystalline material (DNA's regular and repeating structure counts) and then the resulting image, which just looks like a pattern of dots, is mathematically analyzed to derive the structure that created it. Here's what an X -ray diffraction image of DNA looks like:
That may be good enough for all y'all fancy scientists out there, but the rest of us would feel a lot better seeing a real picture of DNA, and the one you've seen up at the top of this article is the first of its kind. It's an electron microscope image of six strands of DNA wrapped around a seventh (such that it looks like a hexagon in cross-section), because the electron microscope itself is powerful enough to smash through single strands of the molecule. The most difficult part of the process was sample preparation: using a surface covered in water-repelling nanopillars, researchers were able to stretch out the DNA strands nice and straight for the pictures.
We'd all still like to get a snapshot of just one single strand of DNA, and the researchers say it should be possible to do that in the near future: they'll just have to use more sensitive detectors that can respond to electrons fired at low enough energies to leave individual strands intact.