Fabricated using inexpensive and widely available organic pigments used in printing inks and cosmetics, an artificial retina was developed that consists of tiny pixels like a digital camera sensor on a nanometric scale.

The electrical response of the neurostimulation devices to pulses of red light is measured. (Photo: Thor Balkhed)

The artificial retina consists of several thin layers of cells. Light-sensitive neurons in the back of the eye convert incident light to electric signals, while other cells process the nerve impulses and transmit them onwards along the optic nerve to an area of the brain known as the visual cortex. An artificial retina may be surgically implanted into the eye if a person's sight has been lost as a consequence of the light-sensitive cells becoming degraded, thus failing to convert light into electric pulses.

The artificial retina consists of a thin circular film of photoactive material, and is similar to an individual pixel in a digital camera sensor. Each pixel is truly microscopic — about 100 times thinner than a single cell — and has a diameter smaller than the diameter of a human hair. It consists of a pigment of semiconducting nanocrystals. Such pigments are cheap and nontoxic, and are commonly used in commercial cosmetics and tattooing ink.

The photoactive film was optimized for near-infrared light, since biological tissues such as bone, blood, and skin are most transparent at these wavelengths. This raises the possibility of other applications in humans in the future.

The prosthesis is described as a “microscopic doughnut,” with the crystal-containing pigment in the middle and a tiny metal ring around it. It acts without any external connectors, and the nerve cells are activated without a delay. Experiments showed that the device can be used to stimulate not only neurons in the brain, but also neurons in non-functioning retinas.

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