Nanoparticles form DNA-based arrangements

Nanoparticles (NPs) are useful in medical and material applications but are hard to manipulate during assembly. A new study provides a straightforward way to use DNA to arrange NPs into a variety of geometries.

When NPs are arranged into a structure such as a thin sheet, they usually do not distribute uniformly but instead clump together in an unpredictable and uncontrollable way. A major goal of NP research is therefore to find a technique that can organize many different sizes and kinds of NPs into well-known and ordered three-dimensional patterns called lattices.

Ions, or charged particles, bond together, and some researchers have used this fact to arrange ionic NPs into simple lattices. But if you change the particle size or charge, the arrangement will change, so this method is very limited.

DNA is made up of long strings composed of four different nucleotides. These strings are "programmable" in that the order and number of nucleotides in a string can be "written." Each nucleoide bonds to its pair — adenine to thymine and guanine to cytosine. Strands of DNA called polypeptide chains will bond to other strands if the bond patterns are complimentary. The paper by Robert J. Macfarlane and others shows the extensive possibilities of using DNA to control the arrangement of NP's into lattices.

In the DNA method, each NP is surrounded by nucleotides. When the NPs are mixed, the dominating forces are those of attraction between the nucleotides that want to pair up. This means that the way the NPs end up will be predictable by the size, number and programmed bonding characteristics of the DNA nucleotides.

Because the order of the nucleotides can be changed, the NPs can be arranged into many different demonstrated predictable lattices. By changing the length of the nucleotides that link particles together, the spacing in the lattices can be adjusted to accommodate different sized NPs.

One application for lattices of nanomaterial is in plasmonics. Plasmonics is a method of data transfer that incorporates the optical speed of fiber optics but relays data through a wire like conventional electronics.

This type of communication would be faster than electronics but would not require bulky wires like fiber optics. However, the ultra-reflective material necessary for building suitable wires does not exist in nature, so the growing field of plasmonics is heavily reliant on nanomaterial engineering.

Another use of nanomaterials is in catalysis, the speeding up of reactions. Because nanoparticles are so small, they have a large surface area to volume ratio, which means that they react faster than almost any other substance. This has applications in chemistry and beyond.

For instance, thermite grenades made with nanoparticles would produce heat more quickly than ordinary thermite grenades. The catalytic converter on cars would filter toxic output more effectively if it were made more reactive by the inclusion of nanoparticles.

With the new methodology outlined in Macfarlane's paper, DNA nanoparticle self-assembly will likely lead to progress in these and other fields.