Kinetically-controlled synthesis of ultra-small silica nanoparticles and ultra-thin coatings.

The understanding of silica as a polymer-like globule allows us to synthesize ultra-small silica nanoparticles (NPs) via a kinetic controlled process. The synthetic system is quite simple with Tetraethyl orthosilicate (TESO) as the precursor and H2O as the solvent and reactant. The reaction conditions are gentle with a temperature of around 35 to 60 °C with an incubation time of 7-12 hours. The final product of the silica NPs is very uniform and could be as small as 10 nm. The silica NPs can further grow up to 18 nm under the controlled addition of the precursors. Also, these silica NPs can be used as seeds to generate larger silica NPs with sizes ranging from 20 to 100 nm, which can be a useful supplement to the size range made by the traditional Stöber method. Moreover, these ultra-small Au NPs can be used as a depletion reagent or as building blocks for an ultrathin silica coating, which has significant applications in fine-tuning the plasmons of AuNPs and thin spacers for surface enhanced spectroscopies.