Imparting bonds, directional bonds

Colloidal particles have been forced to interact in specific ways that mimic the connectivity of atoms in molecules, greatly increasing the sophistication of structures that can be built from smaller components.

A team from New York University, Harvard School of Engineering & Applied Sciences, Harvard physics department and Dow Chemical Co. engineered chemical “patches” that can form directional bonds using single strands of DNA as glue to which patches could adhere.

Scientists at New York University, Harvard School of Engineering & Applied Sciences, Harvard physics department and Dow Chemical Co. have created new kinds of particles, 1/100th the diameter of human hair, that spontaneously self-assemble into structures resembling molecules.

“What this means is [that] 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.”

These bonds can be manipulated to create colloids of a specific color, size, chemical function or electrical conductivity, producing new materials such as photonic crystals to improve optical displays and boost the speed of computer chips.

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

Researchers have built rudimentary colloid structures in the past; 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 particles’ self-assembly and maintain structural integrity.

“It will be surprising if some of the newly accessible configurations do not yield mechanistic insight into atomic systems or give rise to materials that have previously unknown properties,” wrote Matthew R. Jones and Chad A. Mirkin in a News & Views column that accompanied the article in Nature (doi: 10.1038/nature11564).

A major challenge, they add, will be to expand these methods to generate even more sophisticated structures.