Tiny billionth-of-a-meter sized clusters of gold atoms 鈥� gold 鈥渘anoparticles鈥� 鈥� are being widely studied by scientists. They have many useful potential applications, from carriers for cancer-treatment drugs to digital data storage. But many of these applications, particularly those in electronics, require that the nanoparticles form ordered arrays that can be hard to achieve. At Arizona State University (ASU), researchers have discovered that grids made of DNA strands are excellent templates for neatly organizing gold nanoparticles.

鈥淭he collective properties of nanoparticles are heavily dependent on how the particles are grouped. Achieving an even spacing between the particles is particularly important, but can be difficult,鈥� said the study鈥檚 lead scientist, ASU chemist Hao Yan. 鈥淗owever, when deposited onto a DNA grid the particles fall neatly into patterns with little effort on our part.鈥�

Yan and his research group used gold nanoparticles that were five nanometers in diameter. Rather than being bare, the particles were coated with a layer of DNA 鈥減ieces,鈥� called 鈥淭₁₅ sequences,鈥� which radiated from the particles鈥� surfaces like arms. The scientists then deposited the particles onto lattices formed by two types of cross-shaped DNA 鈥渢iles鈥�, 鈥淎鈥� tiles and 鈥淏鈥� tiles, that bind together in an alternating fashion to form the DNA grid.

At regular intervals, each A tile contained a short single strand (called an 鈥淎₁₅鈥� strand) that protruded out of the tile surface. These strands served as tethering points for the T₁₅-coated nanoparticles, allowing the particles to stick to the DNA surface, a bit like DNA-nanoparticle 鈥淰elcro.鈥�

This configuration caused the nanoparticles to 鈥渟elf assemble鈥� into a square pattern 鈥� each particle sitting on one A tile 鈥� with a nearly constant particle-particle distance of about 38 nanometers. The group confirmed this using an atomic force microscope, a very powerful imaging device.

However, this result, while welcomed by the scientists, wasn鈥檛 exactly what they expected.

鈥淲e were pleased that the gold nanoparticles formed a very regular square pattern, but it wasn鈥檛 quite the pattern we thought we鈥檇 see,鈥� said Yan. 鈥淚f you picture nine DNA tiles forming a square, we predicted that five particles would be organized on the square 鈥� one on each corner and one in the middle. But the pattern we observed lacked that middle particle.鈥�

The scientists guess that this is due to the T₁₅ sequence layer, which effectively increases the diameter of each nanoparticle and, moreover, makes each particle highly negatively charged. As a result, the nanoparticles repel each other if they are too close together, which limits the minimum particle-particle distance. Therefore, a particle located at the center of the square would violate this limit.

In future research, Yan and may try to use this organization method to form more complex nanoparticle arrays, such as denser patterns or patterns of different shapes, by altering the particles鈥� DNA coating.

Citation: 鈥淧eriodic Square-Like Gold Nanoparticle Arrays Templated by Self-Assembled 2D DNA Nanogrids on a Surface,鈥� Nano Lett., Vol. 6, No. 2, 248-251 (2006)

by Laura Mgrdichian, Copyright 2006 糖心视频Org.com