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Graphene Sensor Offers Clear Optical Access to Brain Cells

Blue light shines through brain sensor

Blue light shines through a clear sensor implanted in the brain of a lab animal. (Williams research group, Univ of Wisconsin – Madison)

22 October 2014. Engineers at University of Wisconsin in Madison developed an implanted transparent sensor made with graphene that allows for imaging and diagnostics in the brain requiring line-of-sight access. The team led by electrical engineering professor Zhenqiang Ma and biomedical engineering faculty Justin Williams published its findings this week in the journal Nature Communications.

A continuing problem with current implanted sensors to measure neural activity in the brain, say the researchers, is the composition of the devices, which blocks viewing by imaging and diagnostic technologies. “A traditional implant looks like a square of dots, and you can’t see anything under it,” says Williams in a university statement. “We wanted to make a transparent electronic device.”

Ma, Williams, and colleagues chose graphene as the main material for the electronics in their sensor. Graphene is a carbon material closely related to graphite like that used in pencils, but consists of only a single layer of atoms arrayed in a hexagonal mesh pattern. The material is very light, strong, chemically stable, and can conduct both heat and electricity, with applications in fields such as electronics, energy, and health care.

The Wisconsin device consists of 4 graphene circuits, each fabricated in a wafer, coated with Parylene C, a transparent and biocompatible polymer compound, using chemical vapor deposition. Graphene allows the device to remain extremely thin, even with 4 layers. “It’s got to be very thin and robust to survive in the body,” notes Ma.

The researchers tested the device, called carbon-layered electrode array, or Clear, for optical transparency over the spectrum from infrared to ultraviolet frequencies and found the sensor allows for transmission rates of 90 percent or more. The team also implanted devices in lab rats and mice, and found the devices allow for fluorescent microscope images and three-dimensional optical coherence tomography of the blood vessels in the brain immediately under the sensor. Optical coherence tomography is an imaging technology analogous to ultrasound, but using light rather than sound waves.

The researchers also conducted optogenetics tests in the focal cortical areas of the lab animals where the sensors were implanted. Optogenetics uses light to influence activities of genes sensitive to light. Focal cortical areas are parts of the cerebral cortex often causing seizures in children with epilepsy.

Lab mice with brain cells expressing a channelrhodopsin protein were fitted with Clear sensors in their brains and exposed to blue light, known to stimulate that protein. The results showed at some light intensity levels, nerve cells respond to the blue light exposure.

University of Wisconsin is in the process of patenting the technology. The team believes the Clear device can be a significant help to neuromodulation therapies involving electrical stimulation of brain cells, to treat disorders such as hypertension, epilepsy, and Parkinson’s disease. The device can assist in understanding precise effects of the stimulation, which at present are considered rudimentary.

The researchers are also working with colleagues at University of Illinois-Chicago developing contact lenses with built-in transparent sensors to detect damage to the retina and early stages of disorders such as glaucoma.

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