The field of optogenetics where individual brains cells are made to behave differently when exposed to light has wide-ranging potential. It may one day be used to reverse acquired blindness, alter pain thresholds and even hit the rest button on our biological clocks. With one eye on this emerging area of neuroscience, scientists have developed a device the width of a human hair that can be planted in the brain to deliver light or drugs only where needed, offering better targeted treatments and reduced side effects.

The tiny device features microfluid channels and microscale pumps, and is made to be soft like brain tissue so as not to cause inflammation and neural damage. It also houses four separate chambers for carrying drugs directly to the brain and cellular-scale inorganic light-emitting diode (μ-ILED) arrays, allowing it to shine light on targeted cells. And critically, its functions can be triggered remotely.

"Now, we literally can deliver drug therapy with the press of a button," says Jordan McCall, a graduate student at Washington University in St Louis and member of the research team. "We’ve designed it to exploit infrared technology, similar to that used in a TV remote. If we want to influence an animal’s behavior with light or with a particular drug, we can simply point the remote at the animal and press a button."

The animals McCall refers to are mice, in which he and his team successfully demonstrated the device's capabilities for the first time. One part of the study saw the researchers deliver drugs only to one side the brain. This enabled them to stimulate neurons responsible for movement, which prompted the mouse to begin moving in circles.

In another experiment, the scientists shone light directly onto specific brain cells. These cells were chosen because they expressed light-sensitive proteins that trigger the release of dopamine. The resulting good feelings led the mice to return to the same point in the maze where they had received the treatment. Interestingly, and highlighting the multi-purpose functionality of the device, the researchers were able to negate this action by remotely releasing a drug that blocks the function of the dopamine neurotransmitter.

The scientists say the technology could be used to one day treat pain, epilepsy, depression and other neurological disorders. The success of their latest experiments has them hopeful that the device could be adapted to work in other areas of the body, including organs. In future, they plan to improve on the four chamber design and produce something more like a printer's ink cartridge, so that drugs can be drip-fed to targeted cells as needed over a long time.

"We’ve successfully produced and demonstrated an implantable, cellular-scale microfluidic and micro-optical interface to biology, with application opportunities not only in the brain but in other parts of the nervous system and other organs as well," says the study’s co-author John Rogers, professor of materials science and engineering at the University of Illinois.

The research was published in the journal Cell.