Magnetic assembly of colloidal superstructures with multipole symmetry

• Published in: Nature Vol. 457; no. 7232; pp. 999 - 1002
• Main Authors: Yellen, Benjamin B, Erb, Randall M, Son, Hui S, Samanta, Bappaditya, Rotello, Vincent M
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 19.02.2009; Nature Publishing Group
• Subjects: Atoms & subatomic particles; Biosensors; Colloids; Colloids - chemistry; Cross-disciplinary physics: materials science; rheology; Crystals; Exact sciences and technology; Humanities and Social Sciences; Influence; letter; Magnetic fields; Magnetics; Magnetism; Materials science; Methods of nanofabrication; Microscopy, Electron, Scanning; Microspheres; Models, Biological; multidisciplinary; Nanoparticles; Nanostructures - chemistry; Nanostructures - ultrastructure; Optical properties; Particle Size; Phase transitions; Physics; Properties; Science; Science (multidisciplinary); Self-assembly; Symmetry; Symmetry (Physics); Water - chemistry; United States; Ferromagnetic fluid; Magnetostatics; Photonic crystals; Quadrupoles; Multipole field; Self-assembly; Molecular assembly; Colloidal suspension; DNA; Optical properties; Rings; Assembling; Biosensors; Electrostatics; Magnetic fluids
• ISSN: 0028-0836; 1476-4687; 1476-4679
• DOI: 10.1038/nature07766

The assembly of complex structures out of simple colloidal building blocks is of practical interest for building materials with unique optical properties (for example photonic crystals and DNA biosensors) and is of fundamental importance in improving our understanding of self-assembly processes occurring on molecular to macroscopic length scales. Here we demonstrate a self-assembly principle that is capable of organizing a diverse set of colloidal particles into highly reproducible, rotationally symmetric arrangements. The structures are assembled using the magnetostatic interaction between effectively diamagnetic and paramagnetic particles within a magnetized ferrofluid. The resulting multipolar geometries resemble electrostatic charge configurations such as axial quadrupoles ('Saturn rings'), axial octupoles ('flowers'), linear quadrupoles (poles) and mixed multipole arrangements ('two tone'), which represent just a few examples of the type of structure that can be built using this technique.