Researchers Create First Nanofluidic Transistor

University of California, Berkeley, researchers have invented a variation on the standard electronic transistor, creating the first "nanofluidic" transistor that allows them to control the movement of ions through sub-microscopic, water-filled channels.

A nanofluidic transistor could allow the creation of microscopic chemical plants that operate without moving parts. (Images courtesy Majumdar & Yang labs)

The researchers predict that, just as the electronic transistor became the main component of microprocessors and integrated circuits, so will nanofluidic transistors anchor molecular processors, allowing microscopic chemical plants on a chip that operate without moving parts. No valves to get stuck, no pumps to blow, no mixers to get clogged.

As seen in the diagram, the flow of ions through the liquid inside the nanotube (blue) is shut off by a voltage at the gate (yellow).

One application being explored is cancer diagnosis. A nanoscale chemical analysis chip could, theoretically, take the contents of as few as 10 cancer cells and pull out protein markers that can tip doctors to the best means of attacking the cancer.

One big advantage of nanofluidic transistors is that they could be made using the same manufacturing technology that today produces integrated circuits. Nanofluidic channels could be integrated with electronics on a single silicon chip, with the electronics controlling the operation of the nanofluidics. The only microscale parts of the device are the microchannels for injecting liquid.

The research team constructed a 35-nanometer-high channel between two silicon dioxide plates, and then filled the channel with water and potassium chloride salt. They showed that by applying a voltage across the channel by means of electrodes attached to the plates, they could shut off the flow of potassium ions through the water. This is analogous to the control of electron flow through a transistor by means of a gate voltage.

Such ion manipulations are not possible through microscopic channels because ions in the liquid quickly move to the plates and cancel out the voltage, basically shielding the interior of the liquid from the electric field. Channels less than 100 nanometers across, however, are so small that this shielding doesn't occur, so ions in the bulk liquid can be pushed or pulled by electric voltages.

If the ions are proteins, they can be shuttled through channels lined with fluorescent antibodies for detecting or sensing. If the ions are pieces of DNA, they can be sorted and sequenced. In fact, according to the researchers, any highly sensitive biomolecular sensing down to the level of a single molecule could be performed with nanofluidic transistors. They demonstrated that labeled, charged DNA fragments could be manipulated in their transistor.

A version of the transistor was created using nanotubes with internal diameters of 20 nanometers, proving that the same sort of molecular processing can be done with these innovative structures.

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