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DNA & Gold Nanoparticles Used to Make Cloaking Devices

S u m m a r y :
A new technique combining DNA, nanoparticles, and lithography promises to pave the way to cloaking devices, suggests a new study published in the journal Science.

Fiction into Reality

A new method might merge fiction into reality: the first of its kind, the technique combines the use of DNA, nanoparticles, and lithography to create optical materials that might potentially be able to bend light such that they become invisible. Sci-fi enthusiasts will know that this sounds like something from the figment of imagination of writers and movie-makers; so many of our fictitious superheroes take to cloaking devices to get away from their enemies and other unwanted attention, taking stealth technology to a whole new level. Well, the new study might very well bring us nearer to these worlds.

New method to arrange nanoparticles in 2D and 3D, creating optically active superlattices. Materials made from this would be able to bend different light wavelengths. Photo Credits: Northwestern University.

DNA & Gold Nanoparticles Brought Together

The endeavour is a joint effort from scientists from different fields from Northwestern University. The team has made use of DNA as a tool to arrange gold nanoparticles of varied sizes and structures into two and three dimensions to produce optically active superlattices. More interestingly, the latter can exhibit a range of colours from the visible spectrum, as per the particular configurations depending on the particle type, DNA pattern, and sequence. It’s all about playing with the architecture of it all.

“Architecture is everything when designing new materials, and we now have a new way to precisely control particle architectures over large areas,” says study author Chad A. Mirkin, a chemistry professor. “Chemists and physicists will be able to build an almost infinite number of new structures with all sorts of interesting properties. These structures cannot be made by any known technique.”

Old Method (Lithography) Combined With New Method

The technique relies on top-down lithography, the method behind the manufacture of computer chips, and on a more recent approach known as DNA-driven programmable self-assembly. This study is the first that demonstrates how these two techniques can build an individual particle in 3D. Now, it is hoped that these findings will be used by scientists to make metamaterials to be used for medical and environmental purposes.

Also, lithography is used to drill small holes of one-nanoparticle in width into the polymer, thereby producing landing pads for nanoparticle pieces that have been modified with DNA strands; the pads are meant to preserve the structures growing vertically, and they are modified with one DNA sequence while the gold particles are altered with complementary DNA.

“This approach can be used to build periodic lattices from optically active particles, such as gold, silver and any other material that can be modified with DNA, with extraordinary nanoscale precision,” says Mirkin.

Tuning the Optical Properties

The team ran a number of numerical simulations together with optical spectroscopy techniques to determine which specific nanoparticles superlattices would absorb the different light wavelengths.

The resulting materials are also responsive to stimuli. For instance, the exposure to new conditions (like ethanol solutions of different concentrations) can make DNA strands holding the material together to change in length, which then, in turn, caused a change in colour, from black to red to green, thereby allowing the researchers to manipulate the optical properties.

“Tuning the optical properties of metamaterials is a significant challenge, and our study achieves one of the highest tunability ranges achieved to date in optical metamaterials,” says co-corresponding author Koray Aydin.

“Our novel metamaterial platform—enabled by precise and extreme control of gold nanoparticle shape, size and spacing—holds significant promise for next-generation optical metamaterials and metasurfaces.”

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