DNA makes and breaks particle clumps

Nanotechnology is all about manipulating materials on the molecular scale. Many teams of researchers are using artificial strands of DNA to do so.

Researchers from the University of Dortmund in Germany have devised a way to coax DNA to aggregate and separate gold nanoparticles on demand.

The method could be used in sensors that detect biological substances and activities in the lab and body. It could also be used in programmable materials whose properties can be changed by the addition of a piece of DNA.

DNA is made up of four bases -- adenine, cytosine, guanine and thymine -- attached to a sugar-phosphate backbone. Single strands of DNA join when sequences of bases match up -- adenine with thymine, and cytosine with guanine. Short, artificial strands of DNA can be coaxed to arrange into structures, and DNA strands can be engineered to attach to other materials, then arrange those other materials within a structure.

The researchers used two single-strand sequences of DNA that each attach to a gold nanoparticle, and a third single strand that has three sections. The first two sections of the third strand matches up with each of the nanoparticle strands, gluing them together so the gold nanoparticles they carry are positioned close together. The nanoparticles can be pulled apart again using a third type of DNA strand that matches up with the entire glue strand of DNA. This glue removal strand first attaches to the free third section of the glue strand, then continues until the entire glue strand is pulled free.

The gold nanoparticles range from 17 to 29 nanometers in diameter. A nanometer is one millionth of a millimeter, or the span of 10 hydrogen atoms.

Switchable biomaterials could be practical in 10 to 20 years, according to the researchers. The work appeared in the November 30, 2004 issue of Angewandte Chemie International Edition.