Self-assembly breakthrough offers new promise for microscopic materials by mimicking biology

A new method for self-assembly in particles by physicists at New York University (NYU) offers promise for developing complex and innovative microscopic materials.

A note here that the “particles” exhibiting self-assembly are not subatomic particles – like protons and electrons – but particles like molecules, usually only visible through a microscope.

Such self-assembling of particles is believed to be useful in future drug and vaccine delivery as well as other medical applications.

Self-assembly was initially put forward in the early 2000s as the potential for nanotechnology began to make headlines. By “pre-programing” particles, scientists and engineers would be able to build materials at the microscopic level without human intervention. The particles organise themselves.

Think of it like microscopic Ikea furniture that can assemble itself.

But, don’t get the wrong end of the microscopic stick – this has nothing to do with artificial intelligence or particles with consciousness. The particles are programmed through chemistry.

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This self-assembly is reliably done to great effect if all the pieces being assembled are distinct or different. However, systems with fewer different types of particles are much harder to program. The work done at NYU is aimed at producing self-assembly in these systems.

The NYU physicists reported their breakthrough in the journal Nature. Their research centres on emulsion – droplets of oil in water. Droplet chains are made to fold into unique shapes – called “foldamers” – which can be theoretically predicted from the sequence of interactions between the droplets.

Self-assembly already exists in nature. The team borrowed from what we understand of the physical chemistry of folding in proteins and RNA using colloids – a mixture of two or more substances which are not chemically combined, like an emulsion.

By placing an array of DNA sequences on the tiny oil droplets, which served as assembly “instructions”, the team was able to get the droplets to first form flexible chains before sequentially folding or collapsing via the sticky DNA molecules.

The physicists found that a simple alternating chain of up to 13 droplets, with two different types of oil, self-assembled into 11 two-dimensional ‘foldamers’ and an additional one in three dimensions.

Microscopy images show a chain of alternating blue and yellow droplets folding into a crown geometry through blue-blue, blue-yellow, and finally yellow-yellow interactions, mediated by sticky DNA strands. Microscopic droplets are programmed to interact via sticky DNA strands to uniquely fold into well-defined shapes, as shown here. Credit: The Brujic Lab.

“Being able to pre-program colloidal architectures gives us the means to create materials with intricate and innovative properties,” explains senior author Jasna Brujic, a professor in New York University’s Department of Physics. “Our work shows how hundreds of self-assembled geometries can be uniquely created, offering new possibilities for the creation of the next generation of materials.”

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They say the counterintuitive and pioneering aspect of their research is in requiring fewer building blocks to produce a wide variety of shapes.

“Unlike a jigsaw puzzle, in which every piece is different, our process uses only two types of particles, which greatly reduces the variety of building blocks needed to encode a particular shape. The innovation lies in using folding, similar to the way that proteins do, but on a length scale 1,000 times bigger – about one-tenth the width of a strand of hair. These particles first bind together to make a chain, which then folds,  according to pre-programmed interactions that guide the chain through complex pathways, into a unique geometry,” says Brujic.

“The ability to obtain a lexicon of shapes opens the path to further assembly into larger scale materials, just as proteins hierarchically aggregate to build cellular compartments in biology.”

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