Nature Nanotech. 6, 485–490 (2011)

Since the birth of modern chemistry, chemists have been trying to understand how to join specific atoms to others to create molecules with interesting properties. Some chemists have moved up a length scale as they look to bring nanometre-sized units together, and now a team led by Ted Sargent and Shana Kelley at the University of Toronto have developed a simple method that uses DNA 'bonds' to join various quantum dot 'atoms' together, giving them control over the possible binding partners and valency of the quantum dots.

Credit: © 2011 NPG

They make DNA-functionalized CdTe quantum dots in a simple one-pot method using mercaptopropionic acid (MPA) as a co-ligand, which binds to sites left free by the DNA. The DNA has three distinct domains: 'binding', 'spacer' and 'specific binding'. The binding domain is made up of guanine bases and has a backbone of phosphorothioate linkages, rather than the usual phosphodiester groups found in standard DNA. The simple replacement of oxygen with sulfur increases its binding affinity to cadmium and it preferentially binds to the nanoparticle surface — allowing the specific binding domain to remain free to bind with a complementary fragment from another quantum dot.

The size, and thus optical properties, of the free quantum dots were controlled through reaction time, and their valency was controlled (between one and four) by altering the length of the DNA-binding domain (between twenty and five bases respectively). They were therefore able to create complex ternary structures (pictured) that have optical properties distinct from their components.