Liquid Transistor
Voltage controls fluid transport through nanochannels

Results: University of California, Berkeley, researchers have developed a nano-scale silicon device that acts like a transistor for fluids. By applying a voltage across the device, the researchers stopped and started the flow and controlled the concentration of ions and molecules moving through the device's 35-nanometer-high, one-micrometer-wide channels. In one experiment, the team, led by Arun Majumdar and Peidong Yang, increased the concentration of a dye solution twofold by applying a positive 50 volts across electrodes that intersected the channels.

Why It Matters: One potential application of nanotechnology is diagnostics and sensors that manipulate tiny volumes of liquid to detect and measure very low levels of specific molecules. Such "nanofluidics" need a component that controls the movement of liquids and molecules. The Berkeley device could serve that purpose.

Most other nanofluidic devices allow only the passive movement of ions or molecules. This device permits greater control over the fluid's flow and composition. And because nanofluidic circuits could be made using the same techniques that produce electronic circuits, both can be placed on silicon, making possible the electronic control of chemical processing on a chip.

Methods: The Berkeley team made its device using optical lithography. The nanochannels were connected to three electrodes -- one on each end and one, the gate electrode, spanning and intersecting the nanochannels. The researchers introduced a negatively charged dye into the channels and controlled its transport by applying a positive voltage to the gate electrode. The applied positive charge pulled more of the negatively charged dye ions through the channels, increasing their concentration. The researchers measured the effect of the applied voltage on the dye solution by measuring the change in its fluorescence and from that deducing the change in concentration.

Next Step: The researchers are making nanochannels lined on the inside with receptors for specific biomolecules and using the transistors to build nanofluidic circuits that analyze complex mixtures of biomolecules for potential diagnostic and sensing applications. -- By Corie Lok

Source: Karnik, R., et al. 2005. Electrostatic control of ions and molecules in nanofluidic transistors. Nano Letters 5:943-948.