Bob Michaels

September 26, 2011

3 Min Read
Proton-Based Transistor Could Eventually Be Used to Monitor Biological Processes

Based on the understanding that electronic devices send information using electrons while all living things send signals and perform work using ions or protons, materials scientists at the University of Washington (UW; Seattle) have built a transistor that uses protons, creating a key component for devices that can communicate directly with living things. The study is published in the interdisciplinary journal Nature Communications.

An illustration of the UW proton transistor (a) shows the device overlaid on other components. The magnified image (b) shows the chitosan fibers. (Image by Marco Rolandi, UW)

Devices that connect with the human body's processes are being explored for biological sensing or for prosthetic applications, but they typically communicate using electrons rather than protons or ions. "So there's always this issue, a challenge, at the interface--how does an electronic signal translate into an ionic signal, or vice versa?" remarks Marco Rolandi, a UW assistant professor of materials science and engineering. "We found a biomaterial that is very good at conducting protons and allows the potential to interface with living systems."

In the body, protons activate "on" and "off" switches and play an important role in biological energy transfer. Ions open and close channels in the cell membrane to pump things in and out of the cell. Animals, including humans, use ions to flex their muscles and transmit brain signals. A machine that is compatible with a living system in this way could monitor such processes. Someday it could generate proton currents to control certain functions directly.

A first step toward this type of control is the UW researchers' field-effect transistor, which can send pulses of proton current. Measuring about 5 µm wide, the prototype consists of a gate, a drain, and a source terminal for the current. The UW prototype is the first such device to use protons.

The device uses a modified form of the compound chitosan, which is extracted from squid pen, a structure that survives from when squids had shells. The material is compatible with living things, is easily manufactured, and can be recycled from crab shells and squid pen discarded by the food industry. UW postdoctoral researcher Chao Zhong and UW graduate student Yingxin Deng discovered that this form of chitosan is effective at moving protons. When the chitosan absorbs water and forms hydrogen bonds, protons can move from one hydrogen bond to the next.

Because the current prototype has a silicon base that cannot be used in the human body, the transistor would likely be used first for direct sensing cells in the laboratory, Rolandi states. However, in the long run, a biocompatible version could possibly be implanted directly in living things to monitor, or even control, biological processes directly.

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