Next-generation ‘smart’ nanoparticle systems should be precisely engineered in size, shape and composition to introduce multiple functionalities, unattainable from a single material1,2,3. Bottom-up chemical methods are prized for the synthesis of crystalline nanoparticles, that is, nanocrystals, with size- and shape-dependent physical properties4,5,6, but they are less successful in achieving multifunctionality7,8,9. Top-down lithographic methods can produce multifunctional nanoparticles with precise size and shape control2,3,10,11, yet this becomes increasingly difficult at sizes of ∼10 nm. Here, we report the fabrication of multifunctional, smart nanoparticle systems by combining top-down fabrication and bottom-up self-assembly methods. Particularly, we template nanorods from a mixture of superparamagnetic Zn0.2Fe2.8O4 and plasmonic Au nanocrystals. The superparamagnetism of Zn0.2Fe2.8O4 prevents these nanorods from spontaneous magnetic-dipole-induced aggregation, while their magnetic anisotropy makes them responsive to an external field. Ligand exchange drives Au nanocrystal fusion and forms a porous network, imparting the nanorods with high mechanical strength and polarization-dependent infrared surface plasmon resonances. The combined superparamagnetic and plasmonic functions enable switching of the infrared transmission of a hybrid nanorod suspension using an external magnetic field.
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The authors are grateful for primary support of this work from the NatureNet Science Fellowship offered by the Nature Conservancy for nanoparticle fabrication and morphological, optical and magnetic characterization. Electron-beam lithography to pattern the nanoimprint lithography master stamp was carried out at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the US Department of Energy, Office of Basic Energy Sciences, under contract no. DE-AC02-98CH10886. Optical simulation was supported by the US Air Force Office of Scientific Research MURI grant number FA9550-14-1-0389. Synthesis of Au nanocrystals was supported by National Science Foundation grant no. NSF-561658, and synthesis of Zn0.2Fe2.8O4 nanocrystals was supported by the Catalysis Center for Energy Innovation, an Energy Frontier Research Center funded by the US Department of Energy, Office of Basic Energy Sciences under award no. DE-SC0001004. Magnetometry was performed in facilities supported by the National Science Foundation MRSEC Program under award no. DMR-1120901. The mechanical testing was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering under award no. DE-SC0008135. D.J.M. acknowledges the National Science Foundation Graduate Research Fellowship Program under grant no. DGE-1321851 and Y.Y. was supported by University of Pennsylvania's Department of Materials Science and Engineering Masters Scholars Award.
The authors declare no competing financial interests.
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Zhang, M., Magagnosc, D., Liberal, I. et al. High-strength magnetically switchable plasmonic nanorods assembled from a binary nanocrystal mixture. Nature Nanotech 12, 228–232 (2017). https://doi.org/10.1038/nnano.2016.235
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