GRAPHENE SQUARE

 Graphene not only has remarkable electrical, mechanical and chemical properties, scientists recently discovered that it is also a strong diamagnet that can absorb electromagnetic (EM) energy and dissipate this in the form of heat. Since it is only made of carbon atoms, it is much more lightweight than other EM-shielding materials such as metals, which can also suffer from corrosion. The material is also impermeable thanks to its densely packed hexagonal carbon networks that act as a barrier to water molecules.

 In recent years, researchers have developed wearable contact lenses that can be used in applications like glucose monitoring of tears  to diagnose diabetes or glaucoma, for example. A lens that would shield the eye from EM radiation would be a further advance in the field as our exposure to this type of radiation looks set to increase in the coming years, with the advent of the Internet of Things (IoT) technologies. A lens that would protect the eyes from dehydration at the same would be even better since wearing contact lenses for a long time can sometimes cause dry-eye syndrome.

 A team led by Byung Hee Hong of the Graphene Research Center at Seoul National University has now developed a graphene-based highly conducting contact lens coating that fits the bill here.

Graphene conforms to convex surface of the lens

 The researchers began by synthesizing an atom-thick graphene layer using a technique called chemical vapour deposition on a copper foil. They then transferred the carbon sheet onto the surface of a contact lens with the help of a polymer layer after etching the copper. "Thanks to its outstanding flexibility, graphene can be coated on the convex lens surface and conform to it," explains Hong.

The team tested the EM wave-shielding properties of the coated lens by testing it out on egg whites exposed to strong EM waves inside a microwave oven. The results showed that the EM energy is absorbed by the graphene layer and dissipated as heat throughout it so that damage to the egg white is minimized.

"When the graphene is exposed to EM waves, the electrons in orbital motion induce oscillating magnetic moments in response to the external magnetic field, which efficiently absorbs the EM energy and disperses it as thermal energy," explains Hong. "We can thus evaluate the material's EM absorption efficiency by monitoring the heat produced in the graphene-coated contact lens. We did this by using an IR camera to obtain thermal infrared images after applying EM radiation (of 120 W) on the samples inside a microwave oven for 20 seconds and found that the temperature of the graphene-coated contact lens rapidly increased to more than 45 °C, while a normal lens hardly increased in temperature.

Targeting real-time wireless monitoring of glucose concentration

"We also demonstrated that the graphene layer can offer protection from dehydration by monitoring the change in water evaporation rate from water-filled vials capped with the contact lens," says Hong. "30% less water evaporated from vials capped with the graphene-coated lens when compared with vials capped with a non-coated one.

"We believe that such a lens could make for a new healthcare and bionic platform for wearable technologies in the future,” he tells nanotechweb.org. "For diabetes diagnosis, for example, we are now planning to integrate an active circuit with graphene-based sensors and electrodes for real-time wireless monitoring of glucose concentration in tears in collaboration with a contact lens company (Interojo Inc.)."

The graphene-coated contact lens is described in ACS Nano DOI: 10.1021/acsnano.7b00370.

About the author

Belle Dume is contributing editor at nanotechweb.org

source: http://nanotechweb.org/cws/article/tech/67915