A Versatile Silica Functionalization Strategy for Organic Phase Nanomaterials

Chemical interactions between nanoparticles and their surroundings are governed by their surface chemistry. Therefore, a versatile strategy for surface functionalization that is compatible with a variety of particle compositions would empower nanotechnology research. Silica coating offers a promising approach, but the ease with which silica shells can be synthesized is determined by the initial solution state of the nanoparticle, since the silica sol-gel chemistry typically occurs in an aqueous phase. While protocols for coating water-soluble particles are well-established, protocols for nanomaterials suspended in organic solvents require phase-transfer during the coating process, often leading to inconsistent reproducibility, non-uniform thicknesses, difficulty in producing thin coatings, and particle aggregation during functionalization. Here, we demonstrate that these challenges stem from insufficient stabilization of the organic-phase particles during the phase transfer, and can be overcome by adding excess surface ligands during the silica growth process. The inclusion of these excess ligands sufficiently alters the nanoparticles’ surface chemistry to suppress particle aggregation, allowing deposition of shells as thin as 0.7 nm on a wide range of nanoparticle compositions, sizes, and shapes. The versatility and reproducibility of this approach is illustrated through its application to isotropic magnetite nanoparticles with diameters between 20-28 nm, anisotropic magnetite nanodiscs >200 nm in diameter, and CdSe/ZnS quantum dots. These silica-coated nanomaterials retain their functional properties, and the silica shell can be further modified with application-specific organic moieties. This approach therefore provides a versatile means of stabilizing nanomaterials for applications that demand precise control over their surface chemistry independent of their functional properties.