First Direct Electric Link Between Neurons And Light-sensitive Nanoparticle Film

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First Direct Electric Link Between Neurons And Light-sensitive

Nanoparticle Films Created

http://www.sciencedaily.com/releases/2007/02/070227105129.htm

The world's first direct electrical link between nerve cells and

photovoltaic nanoparticle films has been achieved by researchers at

the University of Texas Medical Branch at Galveston (UTMB) and the

University of Michigan. The development opens the door to applying

the unique properties of nanoparticles to a wide variety of light-

stimulated nerve-signaling devices, including the possible

development of a nanoparticle-based artificial retina.

Nanoparticles are artificially created bits of matter not much

bigger than individual atoms. Their behavior is controlled by the

same forces that shape molecules; they also exhibit the bizarre

effects associated with quantum mechanics. Scientists can exploit

these characteristics to custom-build new materials " from the bottom

up " with characteristics such as compatibility with living cells and

the ability to turn light into tiny electrical currents that can

produce responses in nerves.

That's what the UTMB and Michigan researchers did, using a process

devised by Michigan chemical engineering professor Kotov,

one of the authors of a paper on the research appearing in the

current issue of Nano Letters. The process starts with a glass plate

and then builds a layer-by-layer sandwich of two kinds of ultra-thin

films, one made of mercury-tellurium nanoparticles and another of a

positively charged polymer called PDDA. The scientists then added a

layer of ordinary clay and a cell-friendly coating of amino acid,

and placed cultured neurons on the very top.

When light shines on them, the mercury-tellurium nanoparticle film

layers produce electrons, which then move up into the PDDA film

layers and produce an upward-moving electrical current. " As you

build up the layers of this, you get better capabilities to absorb

photons and generate voltage, " said UTMB research scientist Todd

Pappas, lead author on the Nano Letters paper. " When the current

reaches the neuron membrane, it depolarizes the cell to the point

where it fires, and you get a signal in the nerve. "

Although light signals have previously been transmitted to nerve

cells using silicon (whose ability to turn light into electricity is

employed in solar cells and in the imaging sensors of video

cameras), nanoengineered materials promise far greater efficiency

and versatility.

" It should be possible for us to tune the electrical characteristics

of these nanoparticle films to get properties like color sensitivity

and differential stimulation, the sort of things you want if you're

trying to make an artificial retina, which is one of the ultimate

goals of this project, " Pappas said. " You can't do that with

silicon. Plus, silicon is a bulk material -- silicon devices are

much less size-compatible with cells. "

The researchers caution that despite the great potential of a light-

sensitive nanoparticle-neuron interface, creating an actual

implantable artificial retina is a long-range project. But they're

equally hopeful about a variety of other, less complex applications

made possible by a tiny, versatile light-activated interface with

nerve cells -- such things as new ways to connect with artificial

limbs and other prostheses, and revolutionary new tools for imaging,

diagnosis and therapy.

" The beauty of this achievement is that these materials can be

remotely activated without having to use wires to connect them. All

you have to do is deliver light to the material, " said Professor

Massoud Motamedi, director of UTMB's Center for Biomedical

Engineering and a co-author of the paper. " This type of technology

has the ability to provide non-invasive connections between the

human nervous system and prostheses and instruments that are

unprecedented in their flexibility, compactness and reliability, "

Motamedi continued. " I feel that such nanotools are going to give

the fields of medicine and biology brand-new capabilities that it's

hard to even imagine now. "

Other authors of the paper include University of Michigan graduate

students W.M. Shan Wickramanayake and Jan, as well as UTMB

neuroscience and cell biology professor Malcolm Brodwick. The

National Science Foundation provided funding for this research.