Question: how are nanoparticles formed?

Paige Brown answered on 12 Mar 2012:

Hey Guys!!

Nanoparticles can be formed in several different ways. Some ways, called ‘top-down synthesis’, use tools or machines to create tiny objects from bigger ones, like whittling down a piece of wood until it is at the nanoscale. But by far the more useful way to create nanoparticles today is called ‘bottom-up synthesis’, where we can get nanoparticles to form by getting enough atoms to stick together to form a tiny sphere or other nano-shape!

‘Bottom-up synthesis’ techniques often take place in the laboratory as ‘wet chemistry’ procedures. This looks a bit like boiling a large concoction of different wet chemicals in a beaker. If you add some metal powder, for example gold powder, to the reaction, and then add what is called a ‘reducing agent’, and heat these two things up to the point of boiling, then the ‘reducing agent’ will cause the gold atoms to start to stick together and grow into a nanoparticle!! As these particles grow, you can stop the reaction at any time by cooling it down, and get nanoparticles of any shape or size that you want!

The process by which the reducing agent causes the atoms to stick together to start forming a nanoparticle is called ‘nucleation’. You can observe nucleation in everyday life – try sticking your finger into a glass of bubbly water. Do you see that more bubbles seem to form around your finger than in the surrounding liquid? In this case, the interface between your finger and the liquid is serving as a nucleation site, a site where formation of the carbon dioxide bubbles is easiest.

The synthesis of gold nanoparticles is really cool to watch! As the nanoparticles grow, the solutions turns from yellow to blue/purple to red. This happens because gold nanoparticles of different sizes absorb and reflect light at different colors!

Read more about making nanoparticles in the lab here: http://bangordailynews.com/2010/11/07/news/bangor/girl-scouts-explore-engineering-choices-at-umaine/

and here: http://mrsec.wisc.edu/Edetc/nanolab/gold/index.html