Lattice disassembles into nanoparticles

Mesoporous silica nanoparticles are potentially useful for drug delivery, enzyme encapsulation, and other applications. When grown by self-assembly, they tend to aggregate, and it is difficult to control the size and shape of aggregated particles. Andreas Stein and his coworkers at the University of Minnesota, Minneapolis, have now shown that the problem can be overcome by preparing the nanoparticles by disassembly of a macroporous silica lattice (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200604147). This structure is constructed by adding a mixture of surfactant, oxalic acid, and tetraethyl orthosilicate to a colloidal crystal template of poly(methyl methacrylate) spheres. The mixture fills the tetrahedral and octahedral spaces between the spheres and hardens into a solid gel. After the polymer template and surfactant are removed by heating, the silicate gel slowly changes into a silica skeleton that breaks down into discrete mesoporous nanoparticles. The particles gradually develop into cubic and spheroidal shapes to minimize their surface-to-volume ratios. The authors suggest that the nanoparticles-through-disassembly technique could be extended to other 3-D macroporous materials.