Fig. 1.

Directed assembly of magnetic nanoparticles by micropatterned magnetophoretic forces. a Profile of horizontal (blue line) and vertical (green line) components of magnetic force above a magnetic (gray)/nonmagnetic (maroon) composite stamp placed on a NdFeB permanent magnet. Arrows indicate the direction of the resulting forces (towards the magnetic regions). The magnetic features used in the experiments were typically on the order of 100 μm. b A PMMA film containing 12 nm Fe₃O₄ magnetic nanoparticles assembled over an array of magnetic lines in one PDMS stamp. Scale bar = 200 μm. c Scheme of experimental setup for interfering the fields produced by two magnetically patterned PDMS stamps placed between two permanent magnets. One of the stamp-magnet pairs is stationary and the other is manipulated by a motorized translational and/or rotational stage. d A freestanding PMMA film with a pattern of Fe₃O₄ NPs produced by two arrays of parallel lines inclined by θ = 30^o with respect to one another. e Top view of a pattern of Fe₃O₄ NPs forming between two arrays of lines placed at an angle θ = 30^o with respect to one another. Note the particles are localizing exclusively to the rhomboidal regions at lines’ intersections. f The corresponding magnetic field distribution in the plane of the film. Horizontal x, y-components of gradient force over high- and low-field regions are marked with black arrows in the inset—these forces drive the particles to the regions of lines’ intersections. Scale bars in b, d, and e, are 200 μm, 1 mm and 500 μm, respectively