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Scientists develop CdSe/CdS nanorod-nanotube film to stimulate blind retina

Groundbreaking wireless material triggers brain activity in response to light

Researchers from the Hebrew University of Jerusalem with colleagues from the universities of Tel Aviv and Newcastle in the UK have developed a novel approach for retina stimulation using specially tailored CdSe/CdS seeded semiconductor nanorods and carbon nanotubes. Their research was published in the journal Nano Letters.

The retina  - a thin layer of tissue at the inner surface of the eye - is composed of light-sensitive nerve cells that convert images to electrical impulses and send them to the brain. Damage to the retina from macular degeneration, retinitis pigmentosa and other conditions can reduce vision or cause total blindness. In the United States alone, age-related macular degeneration (AMD) affects as many as 15 million Americans, with over 200,000 new cases diagnosed every year.

A variety of medical devices are being developed to counter the effects of retinal disorders by sending visual signals to the brain. But silicon-chip based solutions are typically hampered by their size, use of rigid parts, or requirement of external wiring such as to energy sources. 

The researchers have combined the nanoparticles to create a wireless, light-sensitive, flexible implantable film. The film transforms visual cues to electric signals, mimicking the function of the photo-sensitive cells in the retina. The researchers tested the new device on light-insensitive retinas from embryonic chicks and observed a neuronal response triggered by light. According to the researchers, the new device is compact, capable of higher resolution than previous designs, and is also more effective at stimulating neurons.

The illustration above shows, on the left, a scanning electron microscope image of carbon nanotubes decorated with 40nm x 5nm CdSe/CdS seeded nanorods (the white elongated components). On the upper right  is a recording of retina activity after stimulation with light; the small arrow indicates the time of light pulse. The middle shows the general idea with a neuron sitting on the carbon nanotube film decorated with the CdSe/ CdS nanoparticles. When the film is exposed to light,  the absorption of light by the semiconductor nanoparticles results in local electric field that stimulates the neuron (upper right).

While much work remains until this can provide a practical solution (for instance the team is extending the work for the use of tailored Cd-free semiconductors), with additional research the researchers hope their film will one day effectively replace damaged retinas in humans.

Uri Banin of the Hebrew University said: "This is a pioneering work demonstrating the use of highly tailored semiconductor nanocrystals in activation of biomedical functionalities. We hope this can lead to future implementation of this approach in retinal implants."

'Semiconductor Nanorod-Carbon Nanotube Biomimetic Films for Wire-Free Photostimulation of Blind Retinas' by Lilach Baraket et al, appears in Nano Letters, 2014, 14 (11) DOI: 10.1021/nl5034304

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