Some people do indeed ‘cut’ up larger materials into nanosized objects… this is called the ‘top-down’ approach. But the more popular approach is the ‘bottom-up’ approach. We actually start with things even smaller… ATOMS of a materials, like atoms of gold for example. Then we heat up this solution and add some chemicals that react with the atoms of the material we want (gold for example) and the nanoparticles start to grow ‘out of thin air’, really they start growing up from atoms clashing and sticking together!!
For bottom-up approaches, we can make nanoparticles in solution from the atoms themselves, and we can stop the reaction anytime to get nanoparticles of the size we want!!!! If we stop the reaction early, we get smaller nanoparticles. If we let the reaction go, we can grow larger nanoparticles!! If we make the reaction go fast or slow, we can often determine the SHAPE of the nanoparticle that grows!!!!!!!