When it comes to sending and receiving information, man-made devices utilize negatively-charged particles commonly known as electrons. Biological systems such as human bodies, on the other hand, use protons via positively charged hydrogen atoms or ions. This would indicate that there is something of a language barrier, when we try to develop electronic devices that can communicate with living systems. That barrier could be on its way down, however, as scientists from the University of Washington have developed a transistor that can conduct pulses of protons - and they've done it with some help from our friends the cephalopods.
The prototype device is tiny, at just 5 microns in width - about one twentieth the width of a human hair. It is a field-effect transistor, in that it incorporates a gate, a drain and a source terminal for the current. Its proton current can be switched on and off, just like the electron current in a regular field-effect transistor.
Its active ingredient is chitosan, which is derived from chitin, a compound found in squid pen (part of the squid's body that is left over from when they had shells) and crustacean shells. Chitosan is very good at moving protons, and it forms numerous hydrogen bonds as it absorbs water, the protons then hopping from one bond to the next. The compound is biocompatible, is reportedly easy to manufacture, and can be extracted from squid pens and crab shells discarded by the food industry.
While the current version has a silicon base, future incarnations could be made completely biocompatible. In the immediate future, it could be used to study cells in laboratories. Down the road, however, it could conceivably be used to monitor or control biological processes within the body, or even to control prosthetic limbs.
Chitosan is also, incidentally, the active ingredient in experimental self-healing paint.