Engineers open new field of inquiry in bioelectronics

A device created by Yale University engineers could open a new field of inquiry in bioelectronics, or the merging of biological and electronic systems.

The device, a nanoscale fluidic diode, can tightly control the flow of ions in fluids, such as sodium in water. It could serve as a building block for large-scale circuits that manage the flow and concentration of ions and molecules in electrolyte solutions, much as biological systems do naturally. These circuits could be useful for future desalination or fluid purification systems, among other applications.

Ions are atoms or groups of atoms that carry an electric charge. Examples include sodium, potassium, calcium and other electrolytes essential for healthy human life.

"Ultimately, this is giving us the tools to do real electronic-biological interfaces," said Mark Reed, professor of electrical engineering and applied physics and the principal investigator of the research team that produced the diode. The team, led by graduate student Weihua Guan, recently published its findings in the online journal Nature.

The team’s diode is analogous to solid-state semiconductor diodes commonly found in consumer electronics. Unlike an electrical diode, which channels electrons in a fixed manner, Guan’s device can alter the concentration and direction of ion flows. It is also the first nanofluidic diode that allows a reconfiguration of the diode’s function after it’s already in place.

"We can create some things here that you can’t do with an electrical device," Reed said. "In the fluidic diodes, we can actually tune that flow over a wide range. It gives us an extra degree of freedom that we don’t have in electronic systems. In a way, it’s the beginning of a transistor-like function."

The team’s diode relies on an electric signal to control the direction in which the ions flow and the concentration of ions within the flow.

Made of silicon and silicon dioxide (essentially sand or glass), the diode measures between 8 and 20 nanometers in height, a fraction of a human hair’s diameter. It is called a field-effect reconfigurable nanofluidic diode, or FERD.

Reed is the Harold Hodgkinson Professor of Engineering & Applied Science & Electrical Engineering at the Yale School of Engineering & Applied Science. Guan is a graduate student in electrical engineering. A co-author on the paper is Rong Fan, assistant professor of biomedical engineering, also of Yale.

A Howard Hughes Medical Institute International Student Research Fellowship helped support the research.