Optogenetics: How Brains Of “Genetically Modified” Animals & Men Will Be Wirelessly Remote Controlled
Optogenetics, a recently developed technique uses light to map and control brain activity. Now, a new ultrathin, flexible device laden with light-emitting diodes and sensors, both the size of individual brain cells, promises to make optogenetics completely wireless. Successful integration of advanced semiconductor devices with biological systems will accelerate… an injectable class of cellular-scale optoelectronics that offers such features, with examples of unmatched operational modes in optogenetics, including completely wireless and programmed complex behavioral control over freely moving animals (and humans). The ability of these ultrathin, mechanically compliant, biocompatible devices to afford minimally invasive operation in the soft tissues of the mammalian brain foreshadow applications in other organ systems, with potential for broad utility in biomedical science and engineering.
The implant is a stack of four different optoelectronics devices that the researchers create separately on flexible polymer substrates and then glue on top of one another. The topmost layer is a platinum microelectrode for stimulating and recording from neurons. Below that is a silicon photodetector, followed by a group of four microscale LEDs that are each just 50 by 50 micrometers. Last comes a platinum-based temperature sensor. The filament carrying the stack is glued onto a microneedle with a silk-based glue that dissolves once the device has been injected into the targeted spot, allowing the researchers to retract the microneedle.
The technique for making the membranous devices is not new. Developed a few years ago in Rogers’s lab, it involves growing stacks of thin semiconductor films, peeling them off one at a time with a rubber stamp, and transferring them to plastic substrates.
Scientists could use the multifunctional system to stimulate and sense the brain in a variety of ways, Bruchas explains. The microelectrode can measure the electrical signals produced by neurons, and it can also be used to stimulate them. The photodiodes ensure that the LEDs are working, but they can also be used to detect light signals generated by neurons that have been genetically modified to make certain fluorescent proteins.
The micro-LEDs, which have dimensions comparable to individual neurons, could trigger individual neurons, unlike the fiber-optic implants typically used in optogenetics, which are four times as wide. The researchers could also combine different-colored LEDs on the same device and use them to simultaneously control neurons that have been engineered to react to different colors. Such multiplexing would allow neuroscientists to analyze brain circuits more precisely, Bruchas says. Finally, the temperature sensor monitors the heat generated by the LEDs to prevent the tissue from overheating. more