Scientists from NIST (noted by SpaceDaily) are reporting that using some clever optical trickery such as a "structured illumination field" and a heap of computer processing to reconstruct what the light is scattering off of they can use visible (violet) light to image features as small as 40nm — well within the nanoscale realm.
Speculation: If they push this a little (using UV wavelengths) they may be able to get down into the 20nm realm. That scale is sufficient to see if your nanorobot subassemblies self-assembled properly…
