There are two main approaches to synthesize nanomaterial or nanoparticle. One is top-down approach and another is the bottom-up approach.
Let us discuss these approaches one by one:
1. Top-down approach:
As the name suggests, the top-down approach means from top(larger) to bottom(smaller). This approach is similar to making a statue made of stone. As in making of a statue, a bulk or big piece of stone is taken, similarly in top-down approach; a bulk piece of material is taken. Then carving and cutting is done until desired shape is achieved. Example: Different kinds of lithographic techniques cutting (such as electron beam, photo ion beam or X-ray lithograph cutting), etching, grinding, ball milling and sol gel technique.
2. Bottom-up approach:
As the name suggests, the bottom-up approach means from bottom(smaller) to top or up(larger). In this technique, a nanometric structure is taken then using methods of assembly or self assembly, a mechanism is developed which is larger than where it is started.
Example: all cell use enzymes to create DNA by taking constituent molecules and binding them together to make the final component.