CLEAR transparent graphene micro-ECoG array
CLEAR transparent graphene micro-ECoG array
A surface array with transparent graphene contacts and traces over the brain-facing region. The optical path through the electrode lets researchers record electrical activity while stimulating with light or imaging the vessels beneath it. Gold is still used for the connection pads and initial trace portions, so the entire connected assembly is not invisible.
Published construction
| Field | 2014 paper |
|---|---|
| Electrode sites | 16 |
| Transparent conductor | Four stacked graphene monolayers |
| Parylene-C base | 15 µm |
| Additional parylene-C encapsulation | 10 µm, patterned to expose contacts |
| Rat-size electrode area | 3.1 × 3.1 mm |
| Mouse-size electrode area | 1.9 × 1.9 mm |
| Connector | Zero-insertion-force PCB connector |
| Four-layer graphene sheet resistance | 76 Ω per square |
The two area figures refer to different rodent-size versions. They are not the complete device outline or the size of one contact. No contact pitch or complete 3D geometry is inferred here.
Optical and electrical evidence
The abstract reports more than 90% transmission over the ultraviolet-to-infrared spectrum. The results describe roughly 90% transmission at the 470 and 570 nm wavelengths used for optogenetic applications, measured within a 300-1,500 nm test range. Those descriptions are retained rather than reduced to a single universal transmission number.
In saline, the paper reports average 1 kHz impedance of 243.5 ± 5.9 kΩ for graphene sites versus 188.8 ± 92.9 kΩ for the platinum comparison. The transparent array recorded spontaneous and evoked signals in rodents and allowed fluorescence microscopy and optical coherence tomography of cortical vasculature.
Experiment and limits
The study used four rats and five mice. The paper describes optogenetic evaluation in three Thy1::ChR2 mice and distinguishes the brief light-induced artifact from the later evoked neural response. Transparency does not eliminate light artifacts: strong light on a contact still creates an electrical artifact, and some paradigms may have overlapping artifact and neural response.
Both graphene and platinum implants showed a steep impedance rise in the first ten days. Their changes did not differ significantly over the paper’s implantation period. This does not establish lifetime reliability, human safety or a clinical BCI outcome.
Organization and source
The University of Wisconsin–Madison announcement identifies the local engineering team and collaborators at Wisconsin-Milwaukee and Mahidol University. The animal procedures were approved at Wisconsin–Madison. Published October 20, 2014.
- Park DW, Schendel AA, Mikael S, et al. Graphene-based carbon-layered electrode array technology for neural imaging and optogenetic applications. Nature Communications 5, 5258 (2014). Primary paper, fabrication and rodent experiments.
- University of Wisconsin–Madison. See-through sensors open new window into the brain, October 20, 2014.