Self-Assembling Particles Could Advance Optics

Microparticles engineered to self-assemble spontaneously, much as atoms form into molecules, could lead to enhanced optical displays and speedier computer chips, investigators say.

The new particles, 1/100th the diameter of human hair, were crafted by altering the architecture of colloids — small particles found suspended in liquid and dispersed in common items such as paint, milk, glass and porcelain. The research, performed by scientists at New York University, Harvard School of Engineering & Applied Sciences, Harvard physics department and Dow Chemical Co., appeared in Nature (doi: 10.1038/nature11564).

Scientists have created new kinds of particles, 1/100th the diameter of a human hair, that spontaneously self-assemble into structures resembling molecules. Illustration courtesy of Yufeng Wang and Yu Wang.

Researchers have built rudimentary colloid structures previously; however, they have been limited in their ability to design and assemble these particles into complex 3-D shapes because colloids lack the directional bonds needed to control particle self-assembly and maintain structural integrity.

“What this method aimed to do was to use nature’s properties for atoms and apply them to the colloidal world,” said NYU chemistry professor Marcus Weck.

“Chemists have a whole periodic table of atoms to choose from when they synthesize molecules and crystals,” said Vinothan Manoharan, associate professor of chemical engineering and physics at Harvard. “We wanted to develop a similar 'construction set' for making larger-scale molecules and crystals.”

The team members engineered chemical “patches” that can form directional bonds. To establish bonding capabilities on the patches, they used single strands of DNA to organize small particles. The DNA served as the glue to which particle patches could adhere. These bonds can be manipulated to create colloids of a specific color, size, chemical function or electrical conductivity, leading to the production of new materials such as photonic crystals to improve optical displays and boost the speed of computer chips.

These are electron microscope images of “colloidal atoms,” micron-sized particles with patches that allow bonding only along particular directions. From left: Particle with one patch (analogous to a hydrogen atom); two, three, four (analogous to a carbon atom); five, six and seven patches. Courtesy of Vinothan N. Manoharan and David J. Pine.

"What this means is we can make particles that attach only at the patches, and then we can program them so only specific kinds of particles attach at those patches," said David Pine, an NYU physics professor. "This gives us tremendous flexibility to design three-dimensional structures."

For more information, visit: www.seas.harvard.edu

For another take on self-assembling nanomaterials, see: Nanorope Advances Self-assembling Nanomaterials

To find out about using nanoparticles and DNA for nano-optics, see: DNA Origami Nanolenses to Visualize Single Molecules