Magnetic assembly and patterning of general nanoscale materials through nonmagnetic templates.

Applied magnetic field represents an effective tool to rapidly assemble micro- and nanoscale magnetic objects into defined structures. Ordered assembly is typically achieved by using magnetic micropatterns, for which the downside is that they require advanced microfabrication techniques to produce. In addition, most conventional magnetic assembly strategies are restricted to target objects that possess magnetic properties. Herein we present a general strategy that allows convenient magnetically driven assembly of nonmagnetic objects in defined locations with high spatial resolution. The process involves immersing a polymer relief pattern in a uniformly magnetized ferrofluid, which modulates the local magnetic fields around the pattern. Nonmagnetic target objects dispersed in the same ferrofluid can then be magnetically assembled at positions defined by the polymer pattern. As the nonmagnetic polymer patterns can be conveniently fabricated at low cost through photolithography and soft-lithography processes, our method provides a general yet very effective means to assemble a wide range of nonmagnetic objects with controlled spatial distribution, paving the way toward patterning functional microstructures.