This piece in Nature made my jaw drop:
The highest possible resolution images — about 100,000 dots per inch — have been achieved, and in full-colour, with a printing method that uses tiny pillars a few tens of nanometres tall. The method, described today in Nature Nanotechnology1, could be used to print tiny watermarks or secret messages for security purposes, and to make high-density data-storage discs.
Each pixel in these ultra-resolution images is made up of four nanoscale posts capped with silver and gold nanodisks. By varying the diameters of the structures (which are tens of nanometres) and the spaces between them, it’s possible to control what colour of light they reflect. Researchers at the Agency for Science, Technology and Research (A*STAR) in Singapore used this effect, called structural colour, to come up with a full palette of colours. As a proof of principle, they printed a 50×50-micrometre version of the ‘Lena’ test image, a richly coloured portrait of a woman that is commonly used as a printing standard.
That’s the summary of this paper, whose abstract describes the optical limit of resolution:
The highest possible resolution for printed colour images is determined by the diffraction limit of visible light. To achieve this limit, individual colour elements (or pixels) with a pitch of 250 nm are required, translating into printed images at a resolution of ~100,000 dots per inch (d.p.i.). However, methods for dispensing multiple colourants or fabricating structural colour through plasmonic structures have insufficient resolution and limited scalability. Here, we present a non-colourant method that achieves bright-field colour prints with resolutions up to the optical diffraction limit. Colour information is encoded in the dimensional parameters of metal nanostructures, so that tuning their plasmon resonance determines the colours of the individual pixels. Our colour-mapping strategy produces images with both sharp colour changes and fine tonal variations, is amenable to large-volume colour printing via nanoimprint lithography, and could be useful in making microimages for security, steganography, nanoscale optical filters, and high-density spectrally encoded optical data storage.
Also, I just discovered that you can read PDF papers/articles in ReadCube. Try it for the paper above here.