According to Phys.org, researchers at Harvard's Wyss Institute have built self-assembling nanocages comprised of DNA. 

This image, found with the article on Phys.org, shows the DNA 3-D figures the scientists have made and imaged with the PAINT DNA technique. Each structure is composed of DNA tripods that attach end-to-end, forming polygons.

The researchers hope to use this for several medical applications, such as highly localized drug administration with metal coating, but currently are working to ensure the stability of the structures and the DNA. Although DNA is a fairly stable molecule in itself, common enzymes and components of the extra-cellular matrix easily disassemble the DNA.

The rightmost cage shown above, the biggest created to date, is about 1-tenth the size of a bacteria cell.

The Abstract for the research, published in Science Magazine, can be found here.