Protonic transistor for more natural neuronal stimulation

As described in the September issue of Nature Communications, Prof. Rolandi ‘s team at the University of Washington, Seattle has created the first solid-state transistor that controls the flow of protons instead of electrons. This is much more practical for transmission of information in biological tissues than electrons, as protons can freely interact with ions.  The key challenges in developing proton-based electronics are to find the right materials for pumping and conducting the protons. In the developed prototype transistor, the pumping action is mediated by palladium, which can absorb hydrogen and create a hydride that easily accepts and donates protons. The protons then flow through a 3.5-micrometer-wide channel made from nanofibers of chitosan, a polysaccharide extracted from the chitin shells of crustaceans (such as crabs and shrimp). The prototype is built on the silicon substrate, but the final device would probably use a more biocompatible material. The protonic transistor behaves like a traditional field-effect transistor, with the current flowing between the source and drain under the control of the gate. The ability to modulate the current flow in this protonic transistor is rather limited (by a factor of 10) compared to high gain ratios in conventional electronic transistors (x10,000). Unlike these conventional transistors, the protonic one does not have a p-n junction to block the current when the device is off. So, the protonic transistor functions more like a variable resistor than a switch. Despite its limitations, it is a big step toward more natural neuronal stimulation, as the device is easy to fabricate and is more stable than previous attempts, using microfluidics and thin films.