30 nm SiO2 nanoparticle seed synthesis. Following a protocol first published by Hartlen et al. and optimized by Désert et al. 6 mM aqueous L-arginine (100 mL) was added to a 150 mL single-necked, flat-bottomed cylindrical jacketed reaction vessel (internal diameter ~ 4 cm). The solution was put under stirring (150 rpm, (30 × 8) mm Teflon-coated stir bar) under reflux. To this was then added 10 mL tetraethyl orthosilicate which remained in a separate phase to the aqueous solution. The mixture was left until the upper tetraethyl orthosilicate phase completely vanished (∼2 days). A small volume of the seed solution was checked by TEM before use and confirmed to be (30 ± 3) nm (Figure ). The concentration of the sample was determined by dry extraction to be ∼14.5 g L -1 (∼4.7 × 10 14 mL -1 ).