Magnetic Assembly of Superparamagnetic Iron Oxide Nanoparticle Clusters into Nanochains and Nanobundles.

We report on the syntheses of magnetoresponsive, superparamagnetic nanostructures with highly anisotropic shapes, i.e., nanochains of controlled length and their bundles (nanobundles). These nanochains and nanobundles were obtained by the simultaneous magnetic assembly of superparamagnetic nanoparticle clusters (SNCs) and the fixation of the assembled SNCs with an additional layer of deposited silica, produced by a sol-gel process. This low-cost approach provides excellent length control of the short nanochains (approximately 6 or 14 SNCs per nanochain) and fine-tuning of the spacing between the neighboring SNCs inside an individual nanochain. Our magnetically responsive superparamagnetic nanostructures have a controlled aspect ratio, a uniform size, and a well-defined shape, and they express good colloidal stability. This general approach should lead to new, advanced applications of the nanochains and nanobundles in the treatment of cancer and in the ability to magnetically manipulate liquid and photonic crystals.