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Engineers reveal secret to revolutionary transparent sensors


In 2014, engineers from the University of Wisconsin-Madison announced their development of transparent sensors for use in imaging the brain. With the see-through, implantable micro-electrode arrays being years ahead of anything else in the field, this created a buzz and professors Zhenqiang (Jack) Ma and Justin Williams were swamped with requests for the sensors from research groups.

They have now shared the composition of these sensors with the public.

According to a paper published yesterday in Nature Protocols, graphene is the key component in the technology, which has been successfully used in the brain imaging of animals (and can be applied to humans).

“This protocol is the result of the development of the transparent graphene neural electrode array and the enhanced applications that become available as a result of its transparency, including cranial window imaging and optogenetic modulation,” the paper reads.

“The transparent graphene electrode array has been built upon the platinum electrode array, which is fabricated on a Parylene C substrate.”

The researchers have noted the possibility of using indium tin oxide (ITO) or ultrathin metals in place of graphene, as they are easily accessible and commonly used in transparent materials for electronics. However, the transmittances of ITO (~80 per cent) and ultrathin metals (~60 per cent) are inferior to those of graphene (~90 per cent). ITO also does not have a flat transmittance across the visible spectrum and has a steep rolloff in the infrared (IR) spectrum.

According to the researchers, Graphene has a very flat transmittance spectrum, which makes it equally good for optogenetics experiments in the blue spectrum and multiphoton imaging in the IR.

“It is important to use a material that allows through as much transmittance as possible to capture the clearest image, or to allow for the least light loss during optogenetic stimulation. In addition, the brittleness of ITO may limit the conformability of the device to the brain surface,” the paper reads.

An array can be placed anywhere in the brain and applications of graphene technology are not limited to the central nervous system (CNS); graphene technology could be applied to any device interfacing with an electrical biological system, such as the peripheral nervous system (PNS), and visual, muscular or cardiovascular systems, according to the researchers. Other applications include but are not limited to conductive (yet transparent) electrode sites for neural prosthetic systems in the CNS or PNS, electromyography and electrocardiography.

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