Colloidal crystals can change their shape and have memories thanks to DNA, research suggests

A hitherto unknown characteristic of colloidal crystals, highly organized three-dimensional arrays of nanoparticles, has been discovered by Northwestern University researchers very recently.

According to Northwestern University's release, similar to the natural structures found in chameleon skin and butterfly wings, DNA-engineered colloidal crystals demonstrate shape-shifting and structural memory.

The paper was published today in Nature on October 17.

Scientists created colloidal crystals with complementary DNA strands and discovered that dehydration caused the crystals to crumple, causing the DNA hydrogen bonds to dissolve. When the scientists added water, the crystals swiftly went back to their original state.

A colloidal crystal's ability to retain its shape following structural alterations is described in the new study. This ability is not present in other kinds of crystals. Reversible structural alterations in these new materials may trigger dynamic functional alterations that make them helpful in soft robotics, optics, and chemical and biological sensing in reaction to external stimuli.

“The deformed crystal has completely different properties when it’s broken down,” said Northwestern’s Chad A. Mirkin, who led the study.

“But DNA retraces its steps. Imagine if a house was destroyed by a hurricane, but then every nail and board returned to their original places to reform the house after the storm passed. That’s essentially equivalent to what is happening here with these crystals at the nanoscale.”

The DNA sequence controlling the particle-interconnecting particles affects the new property, which is a type of "hyperelasticity linked with shape memory" and affects the structure and compressibility of the object. The crystal can disintegrate and then reform due to its flexibility.

It all started in 1996

The discovery advances the research that Mirkin started in 1996. At that time, his research team described how DNA might be used as a glue to assemble colloidal crystals, some of which had features and structures similar to those of regular crystals found in nature, while others had traits and configurations that had never been observed in nature.

The authors of the article outline a novel technique for creating crystals that are so enormous that they can be seen with the naked eye. These crystals are significantly larger than any that have ever been created previously.

This advancement has allowed these researchers to explore additional applications for crystals as force and chemical detectors in addition to shape memory discoveries.

Abstract

Reconfigurable, mechanically responsive crystalline materials are central components in many sensing, soft robotic, and energy conversion and storage devices. Crystalline materials can readily deform under various stimuli, and the extent of recoverable deformation is highly dependent upon the bond type. Indeed, for structures held together via simple electrostatic interactions, minimal deformations are tolerated. By contrast, structures held together by molecular bonds can, in principle, sustain much larger deformations and more easily recover their original configurations. Here we study the deformation properties of well-faceted colloidal crystals engineered with DNA. These crystals are large in size (greater than 100 µm) and have a body-centered cubic (bcc) structure with a high viscoelastic volume fraction (of more than 97%). Therefore, they can be compressed into irregular shapes with wrinkles and creases, and, notably, these deformed crystals, upon rehydration, assume their initial well-formed crystalline morphology and internal nanoscale order within seconds. For most crystals, such compression and deformation would lead to permanent, irreversible damage. The substantial structural changes to the colloidal crystals are accompanied by notable and reversible optical property changes. For example, whereas the original and structurally recovered crystals exhibit near-perfect (over 98%) broadband absorption in the ultraviolet-visible region, the deformed crystals exhibit significantly increased reflection (up to 50% of incident light at certain wavelengths), mainly because of increases in their refractive index and inhomogeneity.