This combination of optical microscopy and fluorescence imaging shows a layer of biological cells covering a graphene-based transistor array. The experimental device, created by scientists from the Technische Universitaet Muenchen and the Juelich Research Center, is the first of its kind to prove capable of recording signals generated by living cells, with good spatial and temporal resolution. With this demonstration, the researchers have opened the way to further investigation of the feasibility of using graphene-based bioelectronics for potential future applications such as neuroprosthetic implants in the brain, the eye, or the ear. Image: TU Muenchen |
Researchers have demonstrated, for the first time,
a graphene-based transistor array that is compatible with living biological
cells and capable of recording the electrical signals they generate. This
proof-of-concept platform opens the way for further investigation of a
promising new material. Graphene’s distinctive combination of characteristics
makes it a leading contender for future biomedical applications requiring a
direct interface between microelectronic devices and nerve cells or other
living tissue. A team of scientists from the Technische Universitaet Muenchen
and the Juelich Research Center
published the results inl Advanced Materials.
Today, if a person has an intimate and dependent
relationship with an electronic device, it’s most likely to be a smart phone;
however, much closer connections may be in store in the foreseeable future. For
example, “bioelectronic” applications have been proposed that would
place sensors and in some cases actuators inside a person’s brain, eye, or ear
to help compensate for neural damage. Pioneering research in this direction was
done using the mature technology of silicon microelectronics, but in practice
that approach may be a dead end: Both flexible substrates and watery biological
environments pose serious problems for silicon devices; in addition, they may
be too “noisy” for reliable communication with individual nerve
cells.
Of the several material systems being explored as
alternatives, graphene seems very well suited to bioelectronic applications: It
offers outstanding electronic performance; is chemically stable and
biologically inert; can readily be processed on flexible substrates; and should
lend itself to large-scale, low-cost fabrication. The latest results from the
TUM-Juelich team confirm key performance characteristics and open the way for
further advances toward determining the feasibility of graphene-based
bioelectronics.
The experimental setup reported in Advanced
Materials began with an array of 16 graphene solution-gated field-effect
transistors (G-SGFETs) fabricated on copper foil by chemical vapor deposition
and standard photolithographic and etching processes. “The sensing
mechanism of these devices is rather simple,” says Jose Antonio Garrido, PhD,
a member of the Walter Schottky Institute at TUM. “Variations of the
electrical and chemical environment in the vicinity of the FET gate region will
be converted into a variation of the transistor current.”
Directly on top of this array, the researchers
grew a layer of biological cells similar to heart muscle. Not only were the
“action potentials” of individual cells detectable above the
intrinsic electrical noise of the transistors, but these cellular signals could
be recorded with high spatial and temporal resolution. For example, a series of
spikes separated by tens of milliseconds moved across the transistor array in
just the way action potentials could be expected to propagate across the cell layer.
Also, when the cell layer was exposed to a higher concentration of the stress
hormone norepinephrine, a corresponding increase in the frequency of spikes was
recorded. Separate experiments to determine the inherent noise level of the
G-SFETs showed it to be comparable to that of ultralow-noise silicon devices,
which as Garrido points out are the result of decades of technological
development.
“Much of our ongoing research is focused on further improving the noise
performance of graphene devices,” Garrido says, “and on optimizing
the transfer of this technology to flexible substrates such as parylene and
kapton, both of which are currently used for in vivo implants. We are also
working to improve the spatial resolution of our recording devices.”
Meanwhile, they are working with scientists at the Paris-based Vision Institute
to investigate the biocompatibility of graphene layers in cultures of retinal
neuron cells, as well as within a broader European project called NEUROCARE,
which aims at developing brain implants based on flexible nanocarbon devices.
SOURCE – Technische Universitaet Muenchen