Seeing nanostructures with light is like trying to read Braille by throwing beanbags at the dots and seeing how they bounce off.
A few years ago, it was assumed that light simply could not be used to see things smaller than half its wavelength - which means a large fraction of a micron, not much smaller than a bacterium. But in the past decade, technique after technique has been developed that lets light be used to see nanoscale objects.
A new technique has been announced recently - a very clever way of using "near-field" effects - very roughly equivalent to holding the beanbag instead of throwing it.
If you look down into a water glass made of clear glass and filled with water, you may notice that you don't see through the walls of the glass - instead, you see a reflection back into the glass. But if you put your fingertip on the outside of the glass, you can see your fingerprint. This is called "total internal reflection" and it happens because the light bounces off the boundary between the glass and the air. But in bouncing, an aspect of the light (the "near field") extends slightly beyond the surface, and if your fingertip is right there, the light can interact with it.
Gold nanoparticles are highly effective at scattering light. If a gold nanoparticle were held very near the glass, it could reflect light back to a detector. If there were a very thin pattern of objects between the particle and the glass, then the light scattered by the particle would be affected by the objects. Now, keep in mind that the particle is very small. If it could be scanned back and forth, you could get a pretty precise impression of the objects laid on the glass - even without touching the objects. By controlling the height of the nanoparticle, you could get information about multiple layers of objects.
This is exactly how the microscope works. An atomic force microscope is used to scan the nanoparticle back and forth, up and down, over a slab of material (perhaps sliced from a cell) that's thinner than a wavelength of light. The light that's scattered off the nanoparticle is analyzed, and a 3D picture of the structures inside the slab of material that's being analyzed. The resolution can be as small as a few nanometers.
While I'm talking about microscopes, here's one that's cool because it's so low-tech. It uses an ordinary cell phone camera to record holograms of an image. I don't fully understand this one, so I won't try to explain it. But read the article, check out the cool holographic picture, and you'll get an idea of the kind of data that the system can generate. The cool thing is that somehow this is done without lenses, which means that it costs $10 (not counting the cell phone), suitable for back-country medical diagnostics. (Hat tip to Sander Olson.)
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