Sample Solution

Gao et al (2014) proposed a method for the synthesis of multilayered gold nanoshells, which consist of a gold nanoparticle core, a silicon coating, and a gold outer shell.18 In this method, gold nanoparticles are first synthesised according to methods suggested by Bastus et al, 2011, and then an organosilica layer added. Bastus’ method involves preparing gold seeds, by heating 150mL of 2.2mM sodium citrate solution with stirring, before the addition of 1mL of 25mM chloroauric acid. Methods of growth for nanoparticles of both 30nm and 180nm diameters were suggested, and given that Gao’s method uses 50nm gold nanoparticles, it can be assumed the latter was chosen. In order to grow the seeds to diameters of up to 180nm, the reaction mixture was cooled prior to the addition of a further two 1mL aliquots of 25mM chloroauric acid. 55mL of the solution was removed and replaced with 53mL of water and 2mL of 60mM sodium citrate, in order to dilute the solution.19

In order to form the organosilica layer, 16mL of 50nm colloidal gold was mixed with 100μl of a 100mM mercaptopropyltriethoxysilane (MPTES) solution, and left to stir for 10 minutes, before adding 150μL of 150mM PEG solution, and leaving this to stir for 15 minutes. After being centrifuged to produce a pellet, the pellet was dissolved in water and added to 25μL of MPTES, along with enough ammonia that it would be 25% of the final concentration. This was left overnight in order to produce the organosilica layer on the gold nanoparticles.

The gold-organosilicas were purified against water for 4 hours and then their pH adjusted to 9 using 0.5mM chloroauric acid and 0.01M sodium hydroxide. 4mL of 0.1M sodium borohydride was added in order to reduce the gold before centrifugation to produce gold-gold-organosilicas. To give the final layer of gold, 5mg of potassium carbonate, 750μL of 0.01M chloroauric ac