Scientists at Columbia University have developed flexible, functional, waterproof transistors. These could find use in building miniaturized medical sensors, brain-machine interfaces, or long-term implants.

Silicon-based transistors don't mix well with liquids, because their metallic components can get short-circuited or corroded in a matter of seconds. Unfortunately, waterproofing makes electronic devices bulky and rigid. For devices that must be flexible and waterproof at the same time – such as medical sensors – plastic organic electronics are a promising solution for the future but, for the time being, their performance lags far behind that of their silicon cousins.

A team of researchers led by Dion Knodagholy, Jennifer Gelinas and George Spyropoulos has now developed what promises to be the best of both worlds: a flexible, water-resistant transistor which is also fast enough to allow for high-performance applications like real-time medical monitoring or implantable brain-machine interfaces.

Among the essential components of a transistor are a "source" from which electric charge carriers originate, a "drain" which represents the charges' end-point, and a "channel" connecting the two. The main innovation here is the unique design of the transistor's channel.

"We've made a transistor that can communicate using ions, the body's charge carriers, at speeds fast enough to perform complex computations required for neurophysiology, the study of the nervous system function," says Khodagholy. "Our transistor's channel is made out of fully biocompatible materials and can interact with both ions and electrons, making communication with neural signals of the body more efficient."

The channel is made from electrically-conductive polymers. As ions travel through it, supplemental ions embedded in the channel itself interact with them, effectively shortening the distance that they need to travel on their way to the transistor's drain. According to the researchers, this trick improved the transistor's performance by an order of magnitude compared to similar ionic devices of the same size.

The researchers demonstrated the utility of their technology for electroencephalography (EEG), recording human brain waves from the surface of the scalp. Thanks to the improved size and performance, the contact size of the sensors could be reduced by five orders of magnitude, with the entire device easily fitting between hair follicles and resulting in a much more comfortable experience for the patient.

In terms of bio-monitoring, other uses could include the recording of heart, muscle, and eye movement. Closed-loop devices, such as those used to treat some forms of refractory epilepsy, are also among the possible future applications.

A paper detailing the study was published in the journal Science Advances. More details about the technology are available in the video below.