had Mirkin didn’t set out to discover a new property in matter. But when you’re inventing an alternative to atom-based chemistry, something strange is bound to happen.
For years, he and his colleagues had been exploring something he called “programmable atom equivalents” — tiny nanoparticles, covered with strands of DNA, that mimic the bonding behavior of atoms. But unlike atoms, which are limited to what you find on the periodic table, nanoparticles and DNA bonds can be designed in a nearly infinite number of ways.
Mirkin, a chemist at Northwestern University, had been working with Monica Olvera de la Cruz, a physicist at Northwestern, to explore how these nanoparticles assemble themselves into regular patterns. Such “colloidal” crystals can be found in nature — opals are formed from tightly packed bits of silica — but researchers had been engineering hundreds of others in the lab in the hope of developing colloidal crystals with novel and useful properties.
But an odd thing happened when the teams mixed their tiniest particles with larger ones to make colloidal crystals. The larger particles arranged themselves into a crystal lattice as expected, but the smaller ones roamed freely throughout the structure. And yet, the presence of these tiny, roving particles seemed to be instrumental in keeping the larger particles in place, the teams reported in Science.
“You have these mobile entities, these mobile nanoparticles, that serve as bonding agents,” said David Pine, a New York University physicist who was not involved in the study. “It’s a new property of the material.”
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