Bioinspired 1D superparamagnetic magnetite arrays with magnetic field perception

A bioinspired 1D Fe3O4?NP array was fabricated with high aspect ratio, strict alignment and precise position through employing a micropillar-structured template with asymmetric wettability. To fabricate the micropillar structures, light lithography was processed on nitrogen doped oriented silicon wafers by using a direct laser-writing apparatus which can transfer the computer predefined patterns onto the photoresist-coated wafer. The patterns of photoresist formed after irradiation, followed by deep reactive-ion etching with fluorine-based reagents for 6 min. The geometry of micropillars can be conveniently designed by tuning the parameters of patterns. After resist stripping, the substrates were cleaned using ethanol and acetone. To modify micropillars' sidewalls into hydrophobic state, a 10 μL droplet of SU-8 photoresist liquid was spin-coated onto a flat substrate, yielding a SU-8 thin layer. Subsequently, a micropillar structured template was contacted with the SU-8 loading substrate for 3 min at room temperature followed by peeling off the sticky flat substrate. Through investigating the dewetting process, capillary bridges with 1D configuration has been demonstrated for guiding the assembly behavior of Fe3O4 NPs. Owing to the superparamagnetic nature of Fe3O4 NPs and high-aspect-ratio characteristic of 1D arrays, these assembled structures have been demonstrated with highly anisotropic magnetization, which possess the ability of bioinspired magnetic field perception.