Nav: Home

A sprinkle of platinum nanoparticles onto graphene makes brain probes more sensitive

June 14, 2018

Graphene electrodes could enable higher quality imaging of brain cell activity thanks to new research by a team of engineers and neuroscientists at the University of California San Diego.

The researchers developed a technique, using platinum nanoparticles, to lower the impedance of graphene electrodes by 100 times while keeping them transparent. In tests on transgenic mice, the low-impedance graphene electrodes were able to record and image neuronal activity, such as calcium ion spikes, at both the macroscale and single cell levels. The advance brings graphene electrodes a step closer to being adapted into next-generation brain imaging technologies and various basic neuroscience and medical applications.

Over the past five years, researchers have been exploring graphene electrodes for use in neural implants that can be placed directly on the surface of the brain to record neuronal activity. They have several advantages over the traditional metal electrodes used in today's neural implants. They are thinner and flexible, so they can conform better to brain tissue. They are also transparent, which makes it possible to both record and see the activity of neurons directly beneath the electrodes that would otherwise be blocked by opaque metal materials.

However, graphene electrodes suffer from high impedance, which means electrical current has difficulty flowing through the material. This hinders communication between the brain and recording devices. Readings are noisy as a result. And while there are various techniques to reduce the impedance of graphene, they ruin the material's transparency.

In a new study, an interdisciplinary team of researchers at UC San Diego has developed a technique to engineer graphene electrodes that are both transparent and 100 times lower in impedance. Duygu Kuzum, a professor of electrical and computer engineering at the UC San Diego Jacobs School of Engineering, led the work. Her team developed the low-impedance, transparent graphene electrode arrays. They collaborated with Takaki Komiyama, a professor of neurobiology and neurosciences at the UC San Diego School of Medicine and Division of Biological Sciences, whose team performed brain imaging studies with these electrodes in transgenic mice. The work was published recently in Advanced Functional Materials.

"This technique is the first to overcome graphene's electrochemical impedance problem without sacrificing its transparency," said Kuzum. "By lowering impedance, we can shrink electrode dimensions down to single cell size and record neural activity with single cell resolution."

Lowering impedance

Another important aspect of this work is that it is the first to uncover the root of graphene's high impedance--a fundamental property called quantum capacitance. It is essentially a limit on how many "open seats" graphene has to store electrons. And with a limited number of seats dispersed throughout the material, electrons have fewer paths to travel through.

Finding a workaround to this limit was key to lowering impedance. Kuzum's team found that by depositing platinum nanoparticles onto graphene's surface, they created an alternate set of paths to channel electron flow.

"We chose platinum because it is a well-established electrode material. It has been used for decades due its low impedance and biocompatibility. And it can be easily deposited onto graphene at low cost," said first author Yichen Lu, an electrical engineering Ph.D. student in Kuzum's lab at UC San Diego.

Researchers also determined an amount of platinum nanoparticles that was just enough to lower impedance while keeping transparency high. With their method, the electrodes retained about 70 percent of their original transparency, which Kuzum notes is still good enough to get high quality readings using optical imaging.

Recording brain cell activity in mice

Kuzum's team collaborated with neuroscientists in Komiyama's lab to test their electrodes in transgenic mice. Researchers placed an electrode array on the surface of the cortex. They were able to simultaneously record and image calcium ion activity in the brain.

In their experiments, they recorded the total brain activity from the surface of the cortex. At the same time, researchers used a two-photon microscope to shine laser light through the electrodes and were able to directly image the activity of individual brain cells at 50 and 250 micrometers below the brain surface. By obtaining both recording and imaging data at the same time, researchers were able to identify which brain cells were responsible for the total brain activity.

"This new technology makes it possible to combine macroscale recordings of brain activity, like EEG, with microscopic cellular imaging techniques that can resolve detailed activity of individual brain cells," said Komiyama.

"This work opens up new opportunities to use optical imaging to detect which neurons are the source of the activity that we are measuring. This has not been possible with previous electrodes. Now we have a new technology that enables us to record and image the brain in ways we could not before," said Kuzum.

The team's next steps include making the electrodes smaller and incorporating them into high density electrode arrays.
-end-
Paper title: "Ultralow Impedance Graphene Microelectrodes with High Optical Transparency for Simultaneous Deep Two-Photon Imaging in Transgenic Mice." Co-authors include Xin Liu, Ryoma Hattori, Chi Ren and Xingwang Zhang, all at UC San Diego.

This work was funded by an Office of Naval Research Young Investigator Award (N00014161253), the National Science Foundation (ECCS-1752241, ECCS-1734940), San Diego Frontiers of Innovation Scholars Program, Kavli Institute for Brain and Mind Innovative Research, and the National Institutes of Health (R01 NS091010A, R01 EY025349, R01 DC014690, U01 NS094342, P30EY022589). This work was performed in part at the San Diego Nanotechnology Infrastructure (SDNI) at UC San Diego, a member of the National Nanotechnology Coordinate Infrastructure, which is supported by the National Science Foundation (grant ECCS-1542148).

University of California - San Diego

Related Graphene Articles:

Graphene Flagship publishes handbook of graphene manufacturing
The EU-funded research project Graphene Flagship has published a comprehensive guide explaining how to produce and process graphene and related materials (GRMs).
How to induce magnetism in graphene
Graphene, a two-dimensional structure made of carbon, is a material with excellent mechani-cal, electronic and optical properties.
Graphene: The more you bend it, the softer it gets
New research by engineers at the University of Illinois combines atomic-scale experimentation with computer modeling to determine how much energy it takes to bend multilayer graphene -- a question that has eluded scientists since graphene was first isolated.
How do you know it's perfect graphene?
Scientists at the US Department of Energy's Ames Laboratory have discovered an indicator that reliably demonstrates a sample's high quality, and it was one that was hiding in plain sight for decades.
Graphene is 3D as well as 2D
Graphene is actually a 3D material as well as a 2D material, according to a new study from Queen Mary University of London.
How to purify water with graphene
Scientists from the National University of Science and Technology 'MISIS' together with their colleagues from Derzhavin Tambov State University and Saratov Chernyshevsky State University have figured out that graphene is capable of purifying water, making it drinkable, without further chlorination.
Decoupled graphene thanks to potassium bromide
The use of potassium bromide in the production of graphene on a copper surface can lead to better results.
1 + 1 does not equal 2 for graphene-like 2D materials
Physicists from the University of Sheffield have discovered that when two atomically thin graphene-like materials are placed on top of each other their properties change, and a material with novel hybrid properties emerges, paving the way for design of new materials and nano-devices.
Graphene's magic is in the defects
A team of researchers at the New York University Tandon School of Engineering and NYU Center for Neural Science has solved a longstanding puzzle of how to build ultra-sensitive, ultra-small electrochemical sensors with homogenous and predictable properties by discovering how to engineer graphene structure on an atomic level.
Graphene on the way to superconductivity
Scientists at HZB have found evidence that double layers of graphene have a property that may let them conduct current completely without resistance.
More Graphene News and Graphene Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Teaching For Better Humans 2.0
More than test scores or good grades–what do kids need for the future? This hour, TED speakers explore how to help children grow into better humans, both during and after this time of crisis. Guests include educators Richard Culatta and Liz Kleinrock, psychologist Thomas Curran, and writer Jacqueline Woodson.
Now Playing: Science for the People

#556 The Power of Friendship
It's 2020 and times are tough. Maybe some of us are learning about social distancing the hard way. Maybe we just are all a little anxious. No matter what, we could probably use a friend. But what is a friend, exactly? And why do we need them so much? This week host Bethany Brookshire speaks with Lydia Denworth, author of the new book "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond". This episode is hosted by Bethany Brookshire, science writer from Science News.
Now Playing: Radiolab

Dispatch 3: Shared Immunity
More than a million people have caught Covid-19, and tens of thousands have died. But thousands more have survived and recovered. A week or so ago (aka, what feels like ten years in corona time) producer Molly Webster learned that many of those survivors possess a kind of superpower: antibodies trained to fight the virus. Not only that, they might be able to pass this power on to the people who are sick with corona, and still in the fight. Today we have the story of an experimental treatment that's popping up all over the country: convalescent plasma transfusion, a century-old procedure that some say may become one of our best weapons against this devastating, new disease.   If you have recovered from Covid-19 and want to donate plasma, national and local donation registries are gearing up to collect blood.  To sign up with the American Red Cross, a national organization that works in local communities, head here.  To find out more about the The National COVID-19 Convalescent Plasma Project, which we spoke about in our episode, including information on clinical trials or plasma donation projects in your community, go here.  And if you are in the greater New York City area, and want to donate convalescent plasma, head over to the New York Blood Center to sign up. Or, register with specific NYC hospitals here.   If you are sick with Covid-19, and are interested in participating in a clinical trial, or are looking for a plasma donor match, check in with your local hospital, university, or blood center for more; you can also find more information on trials at The National COVID-19 Convalescent Plasma Project. And lastly, Tatiana Prowell's tweet that tipped us off is here. This episode was reported by Molly Webster and produced by Pat Walters. Special thanks to Drs. Evan Bloch and Tim Byun, as well as the Albert Einstein College of Medicine.  Support Radiolab today at Radiolab.org/donate.