Self-Assembly: How Nanoparticles Make Their Own Arrangements

By Earl Boysen, Nancy C. Muir, Desiree Dudley, Christine Peterson

Nanotechnology scientists recognized that some properties of atoms and molecules enable them to arrange themselves into patterns. For example, if you pour a solution containing organic molecules that have a sulfur atom on one end over a gold surface, the sulfur atoms bond to the gold atoms. This capability is called self-assembly.

Atoms of sulfur bonding to gold atoms as an example of self-assembly.
Atoms of sulfur bonding to gold atoms as an example of self-assembly.

The sulfur atoms are all evenly spaced in an array of rows and columns and that the organic molecules standing up from the surface are all leaning slightly to one side. This effect occurs because the sulfur atoms are sharing electrons with the gold atoms in covalent bonds, but the other electrons surrounding the sulfur atoms repel each other.

This repulsion stops the sulfur atoms from getting too close together. At the same time, the organic molecules are attracted to each other by one of the weaker forces that acts on molecules. This process, called van der Waals bonding, pulls the organic molecules closer together than the sulfur atoms, hence the organic molecules lean slightly to that side.

This mix of covalent bonding, repulsive force, and attractive force results in the molecules, which are functionalized nanoparticles, arranging themselves in a pattern on the gold surface — a perfect example of self-assembly.

Self-assembly is used in many applications, such as

  • Building sensors to detect chemical and biological molecules

  • Creating computer chips with smaller component sizes, which allows more computing power to be packed on a chip

  • Manufacturing diagnostic tools for early detection of diseases