In the world of materials, graphene is the spunky new kid who's annoyingly good at everything he tries. It's super strong, light, functionally non-toxic and thermally and electrically conductive, and is just beginning to show up in commercial products. In the near future, fluorescent quantum dots of the stuff could crop up in clothes, cosmetics, consumer electronics and even cancer treatments. New Atlas spoke to Moti Gross, the CEO of Dotz Nano, an Australian-listed company that's developing new ways for these tiny, glowing, one-atom-thick dots to be made and used.
Founded in 2014, Dotz Nano was built around a new, low-cost method for turning graphene into quantum dots developed by Professor James Tour and his team at Rice University. The company's goal is to expand on that method to make graphene quantum dots (GQDs), and distribute them for use in research and commercial products.
You might recognize "quantum dots" as something manufacturers of TVs and solar cells have been boasting about over the last few years. These tiny semiconducting crystals are typically made of metals like cadmium selenide, and are good at taking in invisible light and emitting it as a certain wavelength of visible light instead.
"A quantum dot is basically a micro-sized disc that absorbs UV light, releases it in the visible light spectrum, and we can change the color that's seen in the visible light spectrum according to the size of the dot," Gross tells New Atlas.
As useful as they can be, producing quantum dots is a difficult and energy-intensive process, and due to the presence of cadmium, some of them are pretty toxic. Companies like Samsung have taken to using safer alternatives in their products, but the dots are still being held back from their full potential by several other issues – many of which, Gross says, can be solved by making them out of graphene instead.
"Graphene quantum dots have other attributes that metallic quantum dots don't have, like electrical conductivity, thermal conductivity, it's 200 times stronger than steel," says Gross. Since graphene is just carbon, the toxicity of GQDs is very low, and the "quantum yield" – that is, the ratio of energy being expended versus the amount of dots being produced – is much higher.
Graphene gets the blues far easier, too. In displays, metallic quantum dots can't replicate the color blue very well, because only the smallest dots, about two nanometers wide, will emit blue, making them notoriously tricky to manufacture.
"The reason they're a problem is because they're so small, the crystalline structure is not big enough to give them a quantum yield that is big enough for their use," Gross explains. "Blue metallic quantum dots are around four to six percent quantum yield, so they don't use blue quantum dots, they use a blue LED backlight. We're able to supply something that metallic quantum dot producers are not."
All of these advantages make graphene quantum dots a far more appealing prospect than their metal cousins, and they could blow open the range of applications for quantum dots in general. Beyond displays, these fluorescent specks could show up in pigments and dyes, cosmetics, anti-counterfeiting technologies, batteries, solar cells, sensors, lights, lasers, water or UV monitoring systems, and bio-imaging technologies.
But the first market that Dotz Nano is targeting with its GQDs is optical brighteners, specifically, the laundry detergent additives designed to make your whites whiter and colors brighter. Gross says that graphene quantum dots are more efficient and cleaner alternatives to the fluorophores widely used in detergents.
"Ninety percent of the fluorophores don't stick to the detergent and washes out, and only a little bit is left," says Gross. "And what happens then is [the remainder] is usually consumed, because UV light is absorbed and it degrades very fast, over a period of several hours. We can make our GQDs stick better to the textile, thereby meaning they have to use fewer GQDs, which is of course a cost saving, and our GQDs last for days instead of hours. Not only that, because it's basically carbon, if it washes out into the environment it doesn't pollute the waste stream."
GQD-based optical brighteners could last even longer if they're embedded directly into the fibers of the fabric, and Gross says that Dotz Nano is working with textile manufacturers in China to weave them in at that early stage. Another application that the company plans to explore is improving anti-counterfeiting technology like that used by casinos, who spray their chips with a solution that glows under UV light.
"If it doesn't glow, that means it's counterfeit," Gross explains. "But the problem is it wears off after a couple of months and they have to replace them all. Taking our product, implementing it into the resin that produces the chips, makes it last for years. Not only that, but utilizing our graphene quantum dots in several colors, we can make a coding spectrum so every casino can have their own signature."
Further down the track, GQDs could help make humidity sensors that are super sensitive, inexpensive and small enough to be incorporated into food packaging.
"We're talking with various wine producers, which can utilize our humidity sensor by printing it on the label, and monitoring the temperature of the wine," says Gross. "So if you're a wine connoisseur, all you have to do is scan the barcode with an app, and you can see the temperature history of the bottle of wine."
But perhaps the most intriguing application is in bio-imaging, where GQDs could be administered to patients to help hunt down and highlight cancer in the body, or be used for targeted drug delivery.
"Bio-imaging is important because with GQDs we can effectively replace some of the isotopes and radioactive materials that are being used," says Gross. "For some reason – we don't know the mechanism yet, but I have some researchers and scientists studying it – it converges on tumors. GQDs are also able to transpose the blood-brain barrier, so it's also good for attacking different types of brain cancers."
But before any of that could come to pass, the way graphene is harvested and converted into quantum dots needed an overhaul. Currently, teams make graphene through a process called the Advanced Hummer's method, which is time-consuming, expensive and inefficient.
"Basically if you take graphite and peel off a layer which is one atom thick, you get graphene," Gross explains. "So if you take that one-atom-thick layer, and you cut off a corner with lateral dimensions, that's 100 atoms by 100 atoms and one atom thick, you get a graphene quantum dot. The problem is that the method is very complex, very expensive, and the production yield is very low, approximately two to three percent."
Instead, Dotz Nano bought into and further developed a better method originally invented by the Tour Lab Group at Rice University. Since graphite and graphene are made of carbon, Professor James Tour and his team looked to coal as a more readily available and cheaper source of carbon and, subsequently, graphene. Eventually, Tour developed a simple chemical process to create GQDs from coal – although the quantum yield was still fairly low, hovering around the 10 percent mark.
"So my research staff in Israel did a lot of work and research," says Gross. "We had a breakthrough a couple of months ago, and today we can produce graphene quantum dots at a level of around 75 percent quantum yield. Which makes it very competitive and comparable to metallic quantum dots."
With those encouraging figures, Dotz Nano is ramping up production of its GQDs, with an eye towards serving several levels of the market: first, selling the dots as a raw material for researchers to save them the time, toll and trouble of making their own. Then, they could be licensed and supplied to companies that want to use them in dyes, detergents, electronics and for a plethora of other purposes.
"There's a lot to do yet," says Moti Gross. "We're moving into commercialization very fast, we're in touch with almost all the major players in each and every targeted market, starting from displays, detergents, anti-counterfeiting, monitoring, all of those applications. It's an interesting adventure every day."
The video below gives an overview of the company and its GQD technology.
Company page: Dotz Nano