Scientists crack the code of nanoparticle edge chemistry, unlocking new materials with protein-like precision

Research from Professor Qian Chen in the Department of Materials Science and Engineering at The Grainger College of Engineering, University of Illinois Urbana-Champaign, and collaborators at the University of Michigan reveals that barely visible, atomic-scale edges on gold nanoparticles are the key to creating an unprecedented variety of polymer patterns on nanoparticle surfaces. The finding opens doors to programmable nanomaterials for medicine, catalysis and beyond.

Every protein in the human body folds and functions because of the precise arrangement of chemical groups on its surface — a molecular patchwork that allows proteins to recognize partners, catalyze reactions, and self-assemble into complex machinery. For decades, scientists have dreamed of endowing synthetic nanoparticles with that same kind of surface complexity. Chen and co-first authors Dr. Xiaoying Lin and Chansong Kim take a major step toward that goal with a secret that was hiding in plain sight, in features so small they were previously overlooked: the edges of nanoparticles.

The work, published in Nature Synthesis, extends the group's previously developed "atomic stencilling" technique to gold nanoparticles shaped like tetrahedra. Atomic stencilling works by masking certain crystal facets of a nanoparticle with iodide ions, then grafting polymer chains only onto the unmasked regions to create distinct surface "patches." Gold tetrahedra posed a challenging puzzle: all four of their faces share the same crystal type ({111} facets), so iodide should mask them entirely, leaving apparently no surface available for polymer attachment. Instead, the researchers found that the six edges of a gold tetrahedron are not atomically sharp but very slightly chamfered, producing narrow strips of a chemically distinct {100} facet just 4.2 nanometers wide. Those slivers remain unmasked and serve as templates for polymer patterning.

"We expected that a tetrahedron, with all four faces being the same crystal type, would be the hardest case to crack — and in some ways it was," said Chen. "But the surprise was that the very features we had been ignoring, those tiny chamfered edges, turned out to be doing all the interesting work. In nanoscience, 'small' and 'insignificant' are not the same thing."

By adjusting the concentration of the iodide masking agent, the concentration of the polymer-anchoring molecule, and the polarity of the solvent, the team produced seven distinct patch patterns on the same tetrahedral shape: patches at single or all four vertices, along individual edges, as a continuous frame around all edges, across entire faces, and in intricate three-petaled "trillium" arrangements. In collaboration with Professor Sharon Glotzer’s group at the University of Michigan, each pattern was predicted by polymer scaling theory and molecular dynamics simulations that explicitly account for the narrow edge geometry, producing a phase diagram covering more than 30 tested conditions that matches experiments quantitatively.

"The fact that theory and simulation could predict all seven patterns was a real watershed moment for us," said Dr. Lin and Kim. "It means we are not just stumbling across new patch patterns — we can design them rationally."

The patchy tetrahedra also self-assemble patch-to-patch into clusters — dimers, trimers, tetramers, and multimers — through corner-, edge-, and face-sharing motifs analogous to those seen in atomic crystal structures. Strikingly, these assembled clusters exhibit chiroptical activity, interacting differently with left- and right-handed circularly polarized light even though the individual building blocks are not themselves chiral. The team confirmed this using photon-induced near-field electron microscopy (PINEM) at Argonne National Laboratory. In collaboration with Professor Nicholas Kotov's group at the University of Michigan, finite-difference time-domain optical simulations further validated the experimentally observed chiroptical response. The calculated g-factor, a measure of chiral optical response, reached approximately 0.1 — higher than most biological and organic molecules.

The broader implication is that subtle shape features in nanoparticles — chamfered edges, truncated vertices, surface steps, twin boundaries — which are often treated as imperfections, can become precise handles for surface patterning when recognized by atomic stencilling. The authors argue that combining the growing library of colloidally synthesized nanoparticles with this technique could yield an expansive palette of patchy designs, with applications in catalysis, plasmonic sensing, biomedicine, and nanofertilizers for agriculture.

"Proteins achieve their remarkable functional diversity not by changing their backbone chemistry but by arranging surface groups in different patterns," said Chen. "We are starting to do something analogous with nanoparticles. Our phase diagram is essentially a map — and it tells us there is a great deal of unexplored territory still ahead."

The U.S. National Science Foundation supported the experimental work and collaborations with the groups of Professor Sharon Glotzer and Professor Nicholas Kotov through cooperative agreement no. 2243104, ‘Center for Complex Particle Systems (COMPASS)’ Science and Technology Center. Another collaborator on this work is Dr. Haihua Liu at Argonne National Laboratory.

Illinois Grainger Engineering Affiliations

Qian Chen is an Illinois Grainger Engineering professor in the Department of Materials Science and Engineering and is affiliated with the Materials Research Laboratory, the Beckman Institute for Advanced Science and Technology, Carl R. Woese Institute for Genomic Biology, the Department of Chemistry, the Department of Chemical and Biomolecular Engineering and the Carle Illinois College of Medicine. She serves as an investigator for Chan Zuckerberg Biohub Chicago and holds the Racheff Faculty Scholar appointment.