Graphene transistors communicate with living cells

It seems that nowadays graphene, which we are contractually obliged to refer to as a ‘wonder material’, is everywhere.  From applications in flexible touchscreens, a new wave of inkjet-printed ultrafast circuits or even a foam used to detect explosives, graphene could be set to revolutionise, well, everything.

Though we’re still awaiting the first applications of graphene to actually become commercially available – this is likely to be smartphone touchscreens, we are told – rarely a day goes by without new potential uses cropping up.

Now, researchers at the Technische Universitaet Muenchen have found a way to make the material even more pervasive.

This is because a team led by Dr Jose Garrido has been working on combining graphene with living cells.  Essentially this means that the material could, in the not-too-distant future, actually be making its way inside your brain.

This is not the first foray into electrical components in conjunction with biology. Many boffins are already working on getting chip and tissue to work together.  However, Garrido reckons that the use of graphene presents a much more viable method for achieving this goal than with silicon based circuitry.

Problems that have hampered silicon development include difficulty opereating in a wet  liquid environment, and being too ‘noisy’ to communicate with nerve cells. Furthermore, silicon is not very flexible, unlike graphene.  This means the researchers believe silicon development could in fact be a “dead end”.   

Graphene, on the other hand, is chemically stable, biologically inert, and can be fabricated relatively cheaply and easily.

Now Garrido’s team has developed, for the first time, a graphene-based transistor array that can be combined with living tissue, and crucially, pick up on electrical signals that are generated. 

This means a direct interface between microelectronic devices and nerve cells – essentially the holy grail of cyborg-style integration of technology into the human body.

This could lead to, for example, sensors inside a person’s brain, eye or ear to help compensate for damaged cells.  Unfortunately it seems that the researchers have not outlined any Deus Ex-style augmentation such as night vision or a bioluminesenct retina at this point.

The method involved using 16 graphene solution gated field effect transistors fabricated on copper foil.  Variations of the electrical and chemical environment around the FET gate could then be sensed and in turn converted in a variation of the transistor current.  

The team grew a layer of biological matter similar to heart muscle cells, and the team found that they could pick up easily the signals transmitted by the nerve cells, in a way that decades of silicon development has struggled to do.

While the research is clearly a long way from real world applications, the team believes that it shows that key performance characteristics are feasible. 

According to Dr Garrido, there are some intriguing applications that being worked on right now.

“Our main goal is the development of grapheme for flexible brain implants,” he told TechEye. “Currently, we are considering two main applications in neuroprosthetics – cortical implants and retinal implants. Both applications will benefit from the flexible technology.”

Garrido tells us developments are in early stages, though working prototypes are expected within the timeframe of just a few years: “Currently, we are at the very beginning,” he said. “In particular, we have to transfer our current technology based on rigid substrates to a more suitable technology based on flexible substrates. We are part of an EU consortium where there are several partners, industrial and hospitals, interested in these applications, and we already have some experience with the technology needed for such applications.”

Fully characterised demonstration prototypes are expected in two to three years,Garrido tells us. After that, “preclinical studies will be necessary before we can expect approval from the FDA and European Medicines Agency.”

Garrido believes that graphene offers serious benefits over silicon-based devices: “The main advantages are chemical stability and biocompatibility of graphene films, facile integration with flexible technology, and the excellent performance of graphene sensors in terms of sensitivity.

“Our preliminary biocompatibility studies, using pure retinal ganglion cells from postnatal rats, has shown that graphene films exhibit similar performance than the standard glass substrates used for cell culture.

“The high carrier mobility in graphene results in devices with very high transconductance, i.e. ‘gate sensitivity’. In comparison to Si counterparts, the graphene FETs exhibit close two orders of magnitude increase in transconductance.

Garrido explains: “It’s not only the signal sensitivity which matters, also the noise level. Our graphene FETs show a noise level which is at the same level that ultra-low noise Si FETs. By improving the graphene growth and fabrication, we expect further lowering of the noise in these devices. We hope to be able to detect signals below one microvolt.

“One important remaining issue concerns long term stability under physiological conditions. It’s worth remembering that we’re talking about a material which is one atom thick. We only have tests performed in-vitro during less than 10 days. Still, we have to perform the long term tests.”