MIT Flips a 20-Year Rule: Floppy Connectors Build Never-Before-Seen Nanoparticle Crystals
Instead of rigid molecular links, the Nature Materials study uses bendy ones that rearrange as particles meet, limiting how many neighbors each particle can grab.
For two decades, materials scientists building crystals out of nanoparticles have followed one rule: make the molecular connectors holding the particles together as rigid as possible. Researchers at MIT and collaborating institutions now report that doing the exact opposite works just as well, and produces crystal structures nobody has seen before.
The findings, described in a paper that will appear in Nature Materials, show that the flexibility and electrical charge of the connectors can decide what structures nanoparticles form. "This is a new approach in nanoparticle assembly that hasn't been investigated before," said Rob Macfarlane, the Richard P. Simmons (1953) Professor in Metallurgy in MIT's Department of Materials Science and Engineering. "It's the exact opposite of what the dogma has been for 20 years: that you need to make connector ligands rigid, and any deviation causes assembly to fail. We showed if you just crank it all the way to the opposite extreme, it works just as well."
The team also included MIT PhD candidate Nicholas Sbalbi, University of Delaware doctoral student Stephen Kronenberger, MIT undergraduate Hana Shinzawa, Matthew Ye PhD '26 and Arthi Jayaraman, a former Delaware professor.
The underlying principle is that how a material's smallest parts are arranged determines how it behaves. Nanoparticles are already used in drug delivery, energy storage, computing and sensors, but turning them into larger organized materials is hard. Without control over how many neighbors each particle binds and in which directions, they tend to pack tightly, which limits the variety of structures and properties scientists can make.
The usual workarounds are changing nanoparticle shapes or patterning sticky regions on their surfaces. Both are complicated and hard to scale. "The methods for defining stickiness that have been developed are always bespoke: They work for one material, at one size scale, in one condition," Macfarlane said. "It's good for studying, but you can't do much with it."
Both approaches also lean on ligands, the molecules that attach to a nanoparticle's surface and link it to its neighbors. Researchers have tried to keep ligands rigid so connections stay at fixed angles, which preserves a target arrangement but narrows what can form.
The MIT team wondered whether near-total freedom to bend could be a new control knob. "We thought, 'Let's do the exact opposite: make the bonds so flexible it doesn't matter what direction they're initially pointing,'" Macfarlane said. "The ligands can then reorganize as the particles come together, and that reorganization itself limits how many neighbors each particle can bind."
That reorganization, the researchers found, steers the particles into arrangements that rigid design never reached. Macfarlane said the result gives scientists a new and counterintuitive tool for building designer materials. The authors point to possible uses in electronics, medicine, energy technologies, agriculture and chemical manufacturing, though those applications remain prospective and the work so far is a demonstration of structure control rather than a finished device.
