Researchers in Singapore have achieved what they claim is the "highest possible resolution" for color laser printing. The team demonstrated the technique by printing the common Lena test image at just 50 by 50 micrometers and around 100,000dpi — any smaller and the light would bounce off each pixel and diffract, resulting in a blurry picture. The pixels are actually constructed from tiny pillars topped with gold and silver nanodisks, but an effect called plasmon resonance means it's possible to define the color of reflected light by varying the dots' diameters and the spaces between them.
We've seen (and questioned the utility of) screens with Retina display-beating resolution, and color print technology has long been able to go beyond what the naked eye can resolve. However, there are other applications for such a dramatic leap in printed resolution: steganographers will no doubt be thrilled at the potential for sending hidden messages, and it could be used for optical data storage or lithographic etchings.