Edible Electronics? Lasers are Bringing “Super Material” Graphene to Everyday Surfaces

This may be the only photo you’ve ever seen of researchers proudly displaying a university-branded potato and coconut.

There’s nothing special about the potato and coconut per se, but their logos deserve a closer look. Unlike the logos on frisbees and other common swag, these logos were not printed, embroidered, or stamped: The logos are made of graphene—a honeycomb-like arrangement of carbon atoms that’s super thin, super tough, and conducts electricity extraordinarily well—and were created by converting the actual surfaces of the potato and the coconut into graphene.

In research recently published in the journal ACS Nano, a team of researchers led by Rice University chemist James Tour describes how to pattern the surface of food, cloth, paper, cork and even Kevlar with graphene by illuminating the material with an infrared laser.

The school-spirited food makes for a good photo op, but the technique behind its creation could have far more exciting applications, according to Tour—applications like tracking food from farm to kitchen with RFID tags, or purifying water. It could likely form the basis for flexible electronics, or even biodegradable and edible electronics, say the authors.

Back in 2014, Tour’s lab reported that by shining a laser on a type of plastic called polyimide, they converted the illuminated surface into graphene. They called the result laser induced graphene, or LIG. More recently, the team converted wood into graphene though a similar process, but one that had to take place inside of a chamber with a controlled atmosphere.

In their latest work, the team describes how to pattern high-quality LIG onto any material with a lot of carbon, as long as the material can withstand the laser. In addition, they show that it can be done in open air, using widely available equipment.

The laser of choice, a carbon dioxide (CO₂) laser, produces the pulses of infrared light that are essential to the process. CO₂ lasers are relatively common, and are often used for engraving, laser cutting, and surgery. It turns out that the key to creating high-quality LIG on carbon-rich materials is “multiple lasing”: hitting the surface with the a series of light pulses at a certain power and wavelength.

When you shine the laser on a sheet of polyimide, the photons stimulate a chemical reaction that rearranges some of the carbon atoms’ bonds into graphene’s characteristic structure. However, the researchers found that if you hit the same part of the sheet multiple times with the laser, more atoms undergo this process and the quality of the graphene increases. For other materials, they found that a first pass of the laser doesn’t produce graphene, but multiple passes do.

Why? In many cases, the first pass of the laser converts the illuminated surface into a disorganized arrangement of carbon atoms called amorphous carbon, while subsequent passes convert this mess into the organized, hexagonal pattern that defines graphene. Through simple multiple lasing, the team showed that LIG can be produced on cotton, cardboard, and other organic matter; to demonstrate the new technology’s versatility, they patterned a tiny, working electrical component right on the surface of a coconut.

The discovery of this two-step process led to another realization: LIG can be applied to any surface that can be carbonized (turned into amorphous carbon). You can carbonize something by charring it—think of the black soot on the outside of a toasted marshmallow. Bread, for example, is carbonized in your toaster. Cloth can be carbonized if you add a flame-resistant layer before exposing it to high heat. Anything that can be charred—from your breakfast to your pajamas and the wood floor in your kitchen—can be patterned with LIG. This is why the technology is so powerful. Imagine being able to quickly and easily pattern sensors, RFID tags, and other electronics right into any of these materials!

Tour’s team is getting right to work on applications for LIG, collaborating with researchers at Ben-Gurion University in Israel to develop antimicrobial water filters through the company TerraForma. If you run electricity through LIG electrodes, their research shows that the electrodes become “bug zappers” for bacteria. LIG also prevents dead bacteria and other microorganisms from building up on wet surfaces, which means that the electrodes can kill and repel bacteria. Combined, these properties hold great promise for water purification systems.

—Kendra Redmond