Nanometre-sized objects with highly symmetrical, cage-like polyhedral shapes, often with icosahedral symmetry, have recently been assembled from DNA1,2,3, RNA4 or proteins5,6 for applications in biology and medicine. These achievements relied on advances in the development of programmable self-assembling biological materials7,8,9,10, and on rapidly developing techniques for generating three-dimensional (3D) reconstructions from cryo-electron microscopy images of single particles, which provide high-resolution structural characterization of biological complexes11,12,13. Such single-particle 3D reconstruction approaches have not yet been successfully applied to the identification of synthetic inorganic nanomaterials with highly symmetrical cage-like shapes. Here, however, using a combination of cryo-electron microscopy and single-particle 3D reconstruction, we suggest the existence of isolated ultrasmall (less than 10 nm) silica cages (‘silicages’) with dodecahedral structure. We propose that such highly symmetrical, self-assembled cages form through the arrangement of primary silica clusters in aqueous solutions on the surface of oppositely charged surfactant micelles. This discovery paves the way for nanoscale cages made from silica and other inorganic materials to be used as building blocks for a wide range of advanced functional-materials applications.
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This project was supported by the National Cancer Institute of the National Institutes of Health under award number U54CA199081. Y.G. and P.C.D. acknowledge financial support from the National Science Foundation (NSF) under grant number 1217867, and Y.G. acknowledges financial support from a 2017 Google PhD Fellowship in Machine Learning. T.A. acknowledges financial support from the Ghent University Special Research Fund (BOF14/PDO/007) and the European Union’s Horizon 2020 research and innovation program (MSCA-IF-2015-702300 and MSCA-RISE-691185). M.Z.T. acknowledges fellowship support from the Ministry of National Education of the Republic of Turkey. This work used shared facilities of the Cornell Center for Materials Research, with funding from the NSF Materials Research Science and Engineering Center program (DMR-1719875), as well as the Nanobiotechnology Center’s shared research facilities at Cornell. The authors thank V. Elser, Y. Jiang and D. Zhang for helpful discussions.