A Bear Frozen in Its Midnight Dream
It was midnight, and it was freezing cold at -170 °C. A little bear was wandering in its wonderful dream: dark sky, moon rising… oh, the moon looks like a cake and there are more and more showing up. Suddenly, all of these became frozen, inscribed in this 17.4 × 17.4 μm micro-image and will stay forever. This is a cryogenic transmission electron microscopy (cryo-TEM) image of a metal-like colloidal crystal recently reported in our manuscript (Science 2019, 364, 1174. DOI:10.1126/science.aaw8237). This crystal consists of 10-nm DNA-functionalized Au particles and numerous tiny Au particles (~1 nm) functionalized with complementary DNA strands. The surprising discovery reveals that the 10-nm particles act as atom equivalents to form a crystalline lattice, while the small particles become classical electron equivalents, which roam through the lattice and hold the crystal together. Acknowledgement on sample preparation: Shunzhi Wang and Ziyin Huang (Mirkin Group).