Nanosheets Roll On Command

Scientists from OIST have developed an optically traceable nanosheet that is responsive to pH.

AsianScientist (Oct. 14, 2014) – Nanosheets that roll up on command could be used for the targeted delivery of cancer drugs. Research demonstrating these unique properties has been published in the journal Applied Materials & Interfaces.

Nanoparticles have the potential to revolutionize the medical industry, but they must possess a few critical properties. First, they need to target a specific region, so that they do not scatter throughout the body. They also require some sort of sensing method, so that doctors and researchers can track the particles. Finally, they need to perform their function at the right moment, ideally in response to a stimulus.

The Nanoparticles by Design Unit at the Okinawa Institute of Science and Technology (OIST) Graduate University is trying to develop new particles with unprecedented properties that meet these requirements. In particular, the work of Dr. Kim Jeong-Hwan has focused on one type of nanomaterial: the nanosheet. Recently, he designed a strong, stable and optically traceable smart 2D material that responds to pH, or the acidity of its surrounding environment.

Nanosheets are unusual amongst nanotechnology because they do not exactly conform to nanoscale. The sheets that Dr. Kim produced are just a few nanometers thick, thin enough to earn the “nano” prefix. But their length and width can be measured in microns, sometimes with surface areas that can be measured in centimeters; much larger than typical nanostructures. Nanosheets’ structure gives them the ability to change shape, from a flat surface to a scroll. Unfortunately, most nanosheets roll and unroll spontaneously.

Dr. Kim tried adding different polymers to his nanosheets to make them responsive. For this experiment, he incorporated a relatively simple polymer that responds to pH. He found that the resulting nanosheet would always curl in basic, high pH conditions, and always flatten in acidic, low pH conditions.

The nanosheets were also responsive to near-infrared light, a wavelength of light that is harmless to humans. Depending on the shape of the nanosheet, the near-infrared radiation bounces back with a different wavelength. Using these optical properties to characterize the nanosheets, Dr. Kim determined that he could approximate pH.

Dr. Kim envisions biomedical engineers wrapping drugs inside of scrolled nanosheets so that when the sheet unrolls, it releases the medicine. For example, pH responsive nanosheets could prove useful for targeting different parts of the human digestive tract, which changes pH between the acidic stomach and basic intestines. Yet this is only the beginning; creating a responsive nanosheet is just a matter of adding the right polymer.

“A nanosheet is like pizza dough,” Dr. Kim said. “Whatever you like to put on it—one topping, two toppings, anything—you can.”

A nanosheet with a heat-sensitive polymer could burn surrounding tumors to destroy them, functioning as a kind of super-specific chemotherapy. Targeting specific tissues is simply a matter of adding the appropriate biomarker, so that the body sends the nanosheet where it belongs.

“There are tons of smart polymers and metals,” Dr. Kim said, explaining the many properties he hopes to incorporate into nanotechnology. “This new structure is composite, which means it allows us to mix all different kinds of components.”

The article can be found at: Kim et al. (2014) Smart Composite Nanosheets with Adaptive Optical Properties.


Source: OIST.
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