Magnetically assisted and accelerated self-assembly of strawberry-like nano/microparticles

Precisely controlling multiple components of functional materials with well- defined shapes and dimensions on the micro/ nanometer scale promises to provide new electronic, magnetic, mechanical, and optical properties for novel sensors, circuits, and other materials application. Here for the first time we introduce a novel method to reliably pattern strawberry-like microspheres by employing magnetically directed and accelerated self-assembly of nano/microparticles in aqueous solution, without the use of a template (such as molds or grooves). The results show that 100-1000 nm paramagnetic "decorating particles" rapidly self-assembled onto the surface of fluorescent 4-5 mu m spherical magnetized "core particles", producing strawberry-like particles with stable and precisely arranged microstructures. Magnetic CrO2 nanorods, approximately 60 nm in diameter and 300 nm long, attached to the nonplanar surface of the 4-5 mu m polystyrene core microspheres, serve as nanometer magnetic traps, so as to attract and confine paramagnetic decorating particles. The ease and speed, with which these particles can be fabricated with the aid of magnetic force, and the flexibility to tailor their chemical and physical properties through the choice of decorating particles, should facilitate their use for practical application in materials science, biology, and technology.