With an excellent ability to conduct heat and electricity, graphene promises to find applications in all kinds of areas. And by crumpling the one-atom-thick sheets of carbon into irregular surfaces, scientists hope to extend its amazing properties even further. A research team at the University of Illinois at Urbana-Champaign has uncovered an exciting new possibility for the so-called wonder material, finding it can serve as the basis of an ultra-sensitive biosensor for early cancer diagnosis.
Scrunching graphene up into a wrinkled mess rather than a neat, flat sheet is a technique being explored by researchers pursuing a number of new technologies. These have included using crumpled balls as components for better batteries, combining them with rubber to form artificial muscles, or bunching crumpled graphene balls together for next-generation energy storage.
What excites the University of Illinois at Urbana-Champaign team is crumpled graphene’s potential in biosensing applications where it could spot disease when other diagnostic tools cannot. The scientists see particular promise when it comes to finding subtle biomarkers for cancer that can hide in nucleic acids like DNA and RNA, as our current methods of detecting them have plenty of room for improvement.
“When you have cancer, certain sequences are over-expressed,” explains Michael Hwang, the first author of the study. “But rather than sequencing someone’s DNA, which takes a lot of time and money, we can detect those specific segments that are cancer biomarkers in DNA and RNA that are secreted from the tumors into the blood.”
This breakthrough stems from a new technique that boosts the electronic properties of graphene. Previously, researchers have attempted to do this by integrating tiny structures into the material, but the scientists believe they have found a better way forward.
The team simply stretched out a thin sheet of plastic and placed the graphene on top of it. Releasing the taut plastic sheet then causes the graphene to contract into a crumpled surface, which creates cavities that act as electrical hotspots with an enhanced ability to attract and trap the DNA and RNA molecules.
“When you crumple graphene and create these concave regions, the DNA molecule fits into the curves and cavities on the surface, so more of the molecule interacts with the graphene and we can detect it,” says graduate student Mohammad Heiranian, a co-first author of the study. “But when you have a flat surface, other ions in the solution like the surface more than the DNA, so the DNA does not interact much with the graphene and we cannot detect it.”
The researchers demonstrated this in experiments involving DNA and cancer-related microRNA contained in both a buffer solution and in undiluted human serum. They report that the crumpled graphene’s performance was “tens of thousands of times” higher than flat graphene when it came to sensing the molecules.
“This is the highest sensitivity ever reported for electrical detection of a biomolecule," Hwang says. "Before, we would need tens of thousands of molecules in a sample to detect it. With this device, we could detect a signal with only a few molecules. I expected to see some improvement in sensitivity, but not like this.”
The researchers say the biosensor could be tweaked to detect a range of proteins and small molecules, depending on the biomarkers they wanted to search for.
“Eventually the goal would be to build cartridges for a handheld device that would detect target molecules in a few drops of blood, for example, in the way that blood sugar is monitored,” says study leader Rashid Bashir. “The vision is to have measurements quickly and in a portable format.”
The team’s research was published in the journal Nature Communications.
