Lets answer the question first. To do so, we need to know the size of the Au particle and to assume it is monodisperse. In fact, one purpose of this application note is to explore the meaning of monodispersity, despite its literal definition, one size. We chose 5 nm diameter Au nanoparticles. Now the earth has an average circumference of 40,000 km or 4 x 1016 nm. So we need 8 x 1015 particles. Thats a lot of particles. Yet, it corresponds to a total volume of just 5 x 10-4 cm3, approximately. Golds density is 19.3 g/cm3. So we need about 10 mg of Au. Not much. Of course, given that high density, it will be hard to keep the particles from sinking into the oceans as we circumscribe the earth, not to mention the tiny tweezers required to manipulate the nanoparticles. But our main goal is to figure out if the size claimed is correct and if the distribution is one size.