Wonder Material Made Practical: Arborsense, Inc.
It’s been called a wonder material. It’s stronger than steel, has high thermal conductivity, exhibits magnetic properties, and is essentially transparent. It has unique electronic properties that could revolutionize the semiconductor industry. What is this material?
Graphene.
Graphene is a two-dimensional, single atom thick sheet of carbon atoms bound together in a hexagonal pattern, closely resembling a honeycomb. Graphene was first isolated and characterized at the University of Manchester by Andre Geim and Kostya Novoselov in 2004, peeling layers of graphene from the graphite of an everyday pencil by using pieces of Scotch tape. After isolating it, they were able to characterize the material, helping to prove concepts that were only theoretical until that point. For their work, these two researchers were awarded the 2010 Nobel Prize in Physics.
So, what is it about graphene that elicits all this hype? Its chemical structure. Pure carbon comes in many forms. Graphite is essentially sheets of graphene stacked up on each other. Diamonds are three-dimensional networks of carbon atoms all bound to their neighbors. Carbon atoms can also be arranged to form sphere-like structures that look like soccer balls. The structure of these carbon forms underlies each form’s unique properties.
Graphene’s form makes it uniquely suitable for a variety of applications. Bonds between carbon atoms are among the strongest across the periodic table, giving graphene its notable strength. Numerous companies have worked to take advantage of this property by incorporating graphene into other materials to make stronger composites. This is very similar to how companies have used carbon fiber in plastics to create strong, lightweight materials. Or how steel rebar is added to strengthen concrete structures.
More recently, researchers and companies have been working to take advantage of another unique property of graphene: its special electronic configuration. Carbon atoms are happiest when they are bound to four neighbors. In graphene, the carbon atoms are bound to only three other carbon atoms, leaving an unbound electron. In simplified terms, this electron flies around the carbon atom, manifesting a pattern that resembles a figure 8 with the carbon atom at the crossing point of the 8 and the bulbous protrusions of the 8 being above and below the atom. When you look at the entire sheet of graphene, you would see each carbon atom having its own figure 8 running through it. The tops and bottoms of these figure 8s would look like a collection of balloons stuck to the chicken wire-like sheet of graphene. Collectively, the free electrons from all of the carbons in the graphene sheet form clouds of free electrons above and below the graphene plane. It’s these clouds of electrons that give graphene its unique electronic properties.
These electron clouds allow for the rapid transmission of electronic signals. Fundamentally, the electronic signals that power so much of today’s technology rely on transmitting a signal by adding or removing an electron from the system. When an extra electron is added, it’s like starting a game of hot potato, where each carbon’s electron cloud wants to pass along the extra electron as soon as it gets handed it. This passing of the electron is like falling dominoes, which transmits the electronic signal. On the other hand, when you remove an electron, the carbon atom that lost its electron isn’t happy because it feels unstable, so it quickly grabs the electron from its neighbor. This process continues as electrons flow to fill the gap, essentially moving the gap in the electron cloud down the line, transmitting the signal.
This ability to rapidly transmit an electrical signal gives graphene a possible application in the semi-conductor industry. However, replacing silicon in the semi-conductor industry is fraught with challenges.
Girish Kulkarni, PhD
An alternative way to use graphene’s properties is being developed by a University of Michigan spin out company called Arborsense, Inc. The company is based on work that Girish Kulkarni did while he was a PhD student in the university’s electrical engineering program and a postdoc in the biomedical engineering department. As a grad student, Girish studied the electronic properties of carbon nanomaterials like graphene and investigated the interaction of organic compounds with pristine nano surfaces. As a postdoc, he developed rapid and sensitive graphene sensors to identify volatile organic compounds. Arborsense is the melding of these two bodies of work.
Arborsense was founded in 2015 with the goal of developing graphene-based sensors that could be used in healthcare. Girish and his colleagues had already demonstrated that graphene could be used to detect over 30 organic compounds with incredible sensitivity, accuracy, and speed. They also knew that the human body produces and releases key analytes or markers, such as ketones in patients with diabetes and cortisol during the response to stress. Importantly, many of these markers are produced as vapors, which can be captured, identified, and measured.
While there are a variety of applications that could be pursued, the company decided to develop their first sensor device to detect alcohol. When people imbibe too much, the body releases unmetabolized alcohol through the skin, where it can then evaporate, providing a good test for the company’s technology.
The wearable device.
Arborsense has developed a graphene-based wearable sensor than can monitor the amount of alcohol being released at the skin. The device is able to do this by taking advantage of graphene’s unique physical properties. When an analyte, such as alcohol, interacts with the graphene surface, it causes a shift in the orientation of the graphene’s electron cloud. Returning to the simplified visual image of the balloons taped to each node of a sheet of chicken wire, imagine the alcohol molecule as a beach ball landing amidst the balloons. The landing beach ball causes the balloons to shift. The pattern of how the balloons shift is unique to the beach ball and would be vastly different for a baseball, soccer ball, or a frisbee. Similarly, different organic analytes create different effects on the graphene’s electron cloud. Knowing this, researchers are able to program the device to accurately identify different analytes. When this property is coupled with graphene’s ability to rapidly transmit a signal and quickly reset, you can produce a device that is accurate, fast, and reusable.
Arborsense has partnered with researchers at the University of Michigan to test its device in humans. The company and its collaborators are in the midst of a large-scale human trial to assess the alcohol-sensing device. In the study, volunteers wear the device on their wrist, much like a fitness tracker, then consume varying amounts of alcohol in a controlled setting. The Arborsense device continuously monitors the amount of alcohol released from the skin. The researchers then compare the device’s data with periodic measurements with a legal-grade breathalyzer.
As the company completes its first human study, the next goal is to evaluate the device in a field trial where people can go about their normal life and the device can take readings over the course of several days. The company is also planning its expansion into additional health monitoring applications. The company has been predominantly supported by small business grants from the National Science Foundation and National Institutes of Health, and it is actively fundraising to help accelerate their expanded product development plans. It will be interesting to see where Arborsense goes next, as it continues to find new uses for the wonder material that is graphene.
Special thanks to Girish Kulkarni, PhD, President of Arborsense, Inc. for taking the time to explain the company’s technology with me. If you have any questions or if you’d like additional details beyond my simplified explanations and metaphors, please reach out to him. He can be contacted at girishkulkarni@arborsenseinc.com and would love to answer any of your questions.