Unique silica enclosures form on micelles

Researchers have created “silicages,” 10-nm-diameter dodecahedral silica enclosures that could serve as carriers for therapeutic drugs or diagnostic agents. Ulrich Wiesner and coworkers at Cornell University created the objects by mixing tetramethyl orthosilicate with pore-expanded cetyltrimethylammonium bromide micelles (Nature 2018, DOI: 10.1038/s41586-018-0221-0). In the mechanism they propose for the process, the silicate starting material forms negatively charged silica clusters that self-assemble into dodecahedra on surfaces of the positively charged micelles. The micelles end up inside the cages but can be removed later to generate hollow enclosures. Wiesner and coworkers used cryo-electron microscopy to confirm the symmetrical structure of the self-assembled objects. In preliminary results, the group shows that vanadium oxide, gold, and silver also self-assemble into cages, suggesting that the approach may extend to a range of inorganic starting materials. The discovery “is a major fundamental achievement,” comments functional nanosystems expert Thomas Bein of the University of Munich. “Packaging and protecting molecules such as fragrances, dyes, and drugs could be intriguing applications,” and expanding the technology to metals and metal oxides “could open up a vast range of other functions and applications, including heterogeneous catalysis and plasmonics,” Bein adds. The Cornell researchers have applied for a patent on the cage-forming technology, and Elucida Technologies, a start-up company they founded, is planning to assess nanomedical applications of the new structures.