Thin is in when it comes to building new medical devices. But biomaterials don't have to struggle with counting calories to reach the desirable size. Instead, researchers at Kansas State University (Manhattan, Kansas) are fabricating graphene – carbon material that is only a single atom thick – to then build an ultra-sensitive, bio-driven DNA sensor and a high-efficiency bacteria-operated battery.
"It's the strongest material in the world at that scale," KSU's Vikas Berry, assistant professor of chemical engineering, told Medical Device Daily. "All the carbon atoms are connected to one another via hybridized bonds."
Graphene was discovered just five years ago and biological interfacing is now taking the material to the next level of development. Berry and his team have to use an atomic force microscope to see and manipulate the carbon sheets that are no bigger than 100 microns across, about the same size as a strand of hair.
What does this material look like? "Black," Berry said. "We have been able to suspend graphene in solution and it looks totally black." Which makes sense because it's exfoliated from graphite (the mineral from which pencil lead is extracted; it's also considered the highest grade of coal). And because graphite is an electrical conductor, the resulting graphene, which also looks a bit like honeycomb or chicken wire, may one day replace silicon as the choice material for semiconductors.
But Berry's team is focused on med-tech applications of the 2-D, chemically modified graphene nanostructures.
The graphene-based invention that's nearest to reality is a DNA sensor for cancer detection. Most current sensors are optical, but a graphene-based sensor would be electrical. When electrons flow on the graphene, they tend to change speed if they encounter DNA. The researchers noticed this change by measuring the electrical conductivity.
"It should not take very long to develop," Berry said. "The preliminary tests have been done. We've measured the sensitivity. We are further developing this to have a sensor that has absolutely no noise. We want to see how sensitive the system is. Our first set of experiments was 20 base pairs. Now we want to see different lengths of DNA and if we can hybridize complementary DNA to different regions of graphene. In one to two years from now, we should see a very sensitive DNA sensor.
"It's a fascinating material to work with," Berry said of his work, which was published in Nano Letters. "The most significant feature of graphene is that the electrons can travel without interruptions at speeds close to that of light at room temperature. Usually you have to go near zero Kelvin – that's about 450 degrees below zero Fahrenheit to get electrons to move at ultra high speeds."
He's using the same graphene to develop a bacteria-operated battery by loading the thin sheets of biomaterial with antibodies and flowing bacteria across the surface.
"We have wrapped bacteria cells with graphene sheets," he said. "The idea, and it's too early for this, is to use this as a interface between bacterial cells and external nanodevice. We want to ultimately have a very strong interfacing with bacterium by a material which is very high in conductivity, which is graphene. By doing this interfacing, electrons produced on the surface can be extracted."
Berry's team found that the graphene, with tethered antibodies, wraps itself around an individual bacterium and remains alive for 12 hours. How does this translate into a battery? By specifically using geobacter, a type of bacteria known to produce electrons, it can be wrapped with graphene to produce electricity.
A resulting battery, he said, is "futuristic work." He said fellow researchers currently working with geobacter to develop batteries have had little success because efficiency is very low.
"But with graphene, you can extract more electrons," he said. "Engineering that into a battery would be the next step.
"Materials science is an incredible field with several exploitable quantum effects occurring at molecular scale, and biology is a remarkable field with a variety of specific biochemical mechanisms," Berry said. "But for the most part the two fields are isolated. If you join these two fields, the possibilities are going to be immense. For example, one can think of a bacterium as a machine with molecular scale components and one can exploit the functioning of those components in a material device."