Human-machine interfaces are constantly improving, but our inability to fully integrate electronics into our bodies stems in part from the very nature of that word — _electron_ics. For the most part, machines relay information using electrons, but living systems use protons and ions. Now a new proton-based transistor built partly from crab shells could open the gates to a new method of communication between machines and biological systems.
Proton transport is important for several biological processes, notably mitochondrial respiration, and living organisms’ electrical signals are modulated using protonic and ionic currents. So a machine that could mimic this type of information transfer could be used, for example, to monitor biological processes. Someday it could even be used to integrate new devices, like prosthetics, or to control biological systems — say, opening ion channels within cells to allow drugs to pass through.
We’ve seen other systems designed to do this, like synaptic transistors, soft biocompatible memristors, and nanoscale devices that use proton-conductive proteins. But those are difficult to build, say Chao Zhong and colleagues at the University of Washington, writing in the journal Nature Communications. It would be useful to have a device based on the type of transistors we all know so well, simply using a different type of current.
In a first step toward functional protonics, Zhong and colleagues built a protonic field-effect transistor. It works exactly like an FET in an electronic system — it has a terminal, a gate and a drain, and it can send pulses of current. The device is partly made from a compound called chitosan, extracted from squid. It can be recycled from crab shells and squid pen discarded by the food industry, according to a UW news release. It is biodegradable, biocompatible and non-toxic, the researchers say. The chitosan absorbs water and forms hydrogen bonds, and protons that are dissociated from maleic acids move along this hydrogen-doped channel.
The main drawback for now is that this FET also uses silicon, so it couldn’t be used in the human body; its main use would likely be direct sensing of cells in a lab. But a biocompatible version using some other type of semiconductor could conceivably be implanted in a living organism, monitoring proton activity and sending it to a protonic — not an electronic — device.