June 15, 2009: Researchers at New York University say they’ve created a method to precisely bind nanoparticles into larger structures that overcomes a “sticky” problem and enables creation of stable, sophisticated microscopic and macroscopic structures.

The work, reported in an advanced online publication by Nature Materials, describes confronting the problem of self-replication: when the number of objects doubles in each cycle it presents a linear challenge when trying to fabricate things microscopic objects with a sophisticated architecture.

Their solution? Coat micrometer particles with short stretches of DNA (“sticky ends”), each with a particular sequence of DNA building blocks; those with complimentary sequences form reversible bonds when a certain temperature is applied. Thus, the particles can be organized in a controlled fashion onto a template, and then released again.

The novel DNA ‘sticky ends’ can form intra-particle loops and hairpins (e.g. schemes II & III), giving more control over the particles’ interactions than conventional sticky ends that can only form inter-particle bridges (scheme Ia). (Source: NYU)

DNA-mediated interactions are known, but binding just subsets of a particle (not the whole thing) into structures has proven difficult. So the researchers at NYU’s Center for Soft Matter Research and in the university’s Department of Chemistry focused on a particular type of DNA sequence that can fold like a hairpin and bind to neighboring “sticky ends,” determining that lowering the temperature rapidly caused the sticky ends to fold up on the particle before they could bind to other sticky ends; this occurred long enough (a few minutes) for the sticky ends to find binding partners on other particles (moved around by optical traps), thus building a structure. “We can finely tune and even switch off the attractions between particles, rendering them inert unless they are heated or held together — like a nano-contact glue,” said Mirjam Leunissen, the study’s lead author, in a statement.

Potential applications listed by NYU include ordering arrays of these particles into optical devices such as sensors and photonic crystals. The same organizational principles also apply to smaller nanoparticles, which have a range of electrical, optical, and magnetic properties useful for applications, NYU noted.

The work was supported by the NSF’s Materials Research Science and Engineering Center (MRSEC) program, the Keck Foundation, and the Netherlands Organization for Scientific Research.