MIT Researchers Show Flexible Ligands Assemble Novel Nanoparticle Crystals

The team replaced stiff DNA or polymer linkers with long, compliant chains bearing charged end groups. In solution, these chains allow nanoparticles to explore a wider configurational space during nucleation, yet the resulting electrostatic and entropic forces still select open lattices rather than close-packed defaults. Experiments tracked assembly via small-angle X-ray scattering and electron microscopy on gold and silica particles ranging 10–50 nm.

This outcome aligns with recent simulations of polyelectrolyte-mediated assembly but extends them to three-dimensional periodic order. Earlier rigid-ligand strategies, dominant since the 2004 DNA-programmed superlattice work, limited accessible symmetries because any deviation from ideal bond angles caused kinetic trapping. Flexible connectors decouple directional specificity from bond stiffness, a principle also emerging in block-copolymer and patchy-particle literature.

The primary limitation remains the absence of long-range orientational control once particles exceed ~100 nm; polydispersity then collapses the lattice. Scaling to device-relevant volumes will require in-situ feedback during assembly. Next, the group plans to couple the method with external fields to bias specific polymorphs and test charge-transport properties in the resulting open lattices.