September 22, 2011 — University of Washington materials scientists are working on a field-effect transistor (FET) that uses protons to communicate, rather than electrons.

Translating an electronic signal to an ionic one, or vice versa, is "a challenge," said Marco Rolandi, a UW assistant professor of materials science and engineering. Protons — positively charged hydrogen atoms that modulate biological energy transfer — or ions — atoms with positive or negative charge that open/close cell membranes for pumping actions — could allow the transistor to communicate directly with biological entities without a complicated interface.

To avoid the complicated electro/bio interface, Rolandi’s team developed a transistor that sends pulses of proton current. The FET comprises a gate, drain, and a source terminal, and measures about 5um wide. "Large, bio-inspired molecules can move protons, and a proton current can be switched on and off," explained Rolandi, saying that the flow is "completely analogous" to a conventional FET’s electronic current.

Figure. The UW device overlaid on a graphic of the other components (left) and a magnification of the chitosan fibers (right). The white scale bar is 200nm. SOURCE: Marco Rolandi, UW.

A modified form of chitosan (a squid pen structure compatible with living things) was used in the device. UW researchers note that the bio-compatible material is easily manufactured and is a waste product of the food industry. Chao Zhong, a UW postdoctoral researcher and Yingxin Deng, a UW graduate student, chose this form of chitosan because it moves protons well. The chitosan absorbs water and forms many hydrogen bonds; protons are then able to hop from one hydrogen bond to the next.

Computer models of charge transport developed by M.P. Anantram, a UW professor of electrical engineering, and Anita Fadavi Roudsari at Canada’s University of Waterloo, were a good match for the experimental results.

The current prototype has a silicon base and could not be used in a human body until a biocompatible replacement material was used. The initial goal of this bio-hybrid FET is to create electronics that could monitor biological actions directly, likely in a lab to start. In the future, these transistors could generate proton currents to control biological functions directly, with biocompatible versions implanted directly in living things.

The study is published online in the interdisciplinary journal Nature Communications. Access it here: http://www.nature.com/ncomms/journal/v2/n9/full/ncomms1489.html. In addition to the researchers mentionned above, co-author Adnan Kapetanovic is a UW materials science and engineering graduate student.

The research was funded by the University of Washington, a 3M Untenured Faculty Grant, a National Cancer Institute fellowship and the UW’s Center for Nanotechnology, which is funded by the National Science Foundation.

Story courtesy of Hannah Hickey, UW. Learn more at http://www.washington.edu/.