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UC Berkeley professor Arun Majumdar and colleagues are designing and building nanofluidic transistor from glass tubes just 100 nanometers in length. (Peg Skorpinski photo)

Traditional transistors are essentially valves that control the flow of electricity to perform calculations. But what if, instead of voltages, a transistor could manipulate the flow of biological molecules like proteins and DNA? Berkeley researchers have developed the world's first device that does just that. Eventually, this nanofluidic transistor could detect cancer in a drop of blood much smaller than the period at the end of this sentence.

Mechanical engineering professor Arun Majumdar and College of Chemistry professor Peidong Yang, in collaboration with their graduate students and visiting professor Hirofumi Daiguji, are designing and building the nanofluidic transistor from glass tubes just 100 nanometers in length. (A nanometer is one-billionth of a meter.)

"Every basic college textbook on fluid dynamics talks about the pressure and velocity of water flowing through a glass pipe," says Majumdar. "We wanted to know if anything unusual happens if the pipe is really small."

While the interactions that occur at the interior surface of glass tubes are of minor importance at the macroscale, the researchers quickly realized that the surface becomes the most important locale for interactions at the nanoscale. Glass tubes are naturally negatively charged, meaning that the material is coated with atoms that have lost an electron. Negatively charged tubes attract positive ions, Majumdar explains. If you fill a tube from one end with a liquid, the negatively charged ions in the liquid are pumped out leaving just the positively charged ions inside. At the macroscale, this effect isn't particularly useful. But with nanotubes of internal diameters of just five to fifty nanometers, the ability to separate the negative and positive ions could enable the glass pipe to become a key component in a nanofluidic transistor, also called a unipolar ionic field-effect transistor.

The silica nanotube in the transmission electron micrograph image has an internal diameter of about 10 nanometers. (courtesy the researchers)

The next step was to fashion a valve, the equivalent of a transistor's gate, to control the ionic current passing through the tube. The researchers placed a fine metal wire on top of the tube to act as an electrode. Applying a voltage to the wire controls the flow of the ions.

"Of course, the gate is too slow to manipulate information like a transistor, but you can push biological molecules through because things like proteins and DNA are all electrically charged," Majumdar says.

Once the researchers fine-tune their control of the ionic flow, they'll line the inside of the tube with biological molecules called antigens. The human body's immune system recognizes antigens as threats, and forms specific antibodies that bind to the foreign molecules. It's this biochemical reaction that signals the immune system to launch an attack on a disease.

To use the nanofluidic transistor as a disease detector, a tiny drop of blood will be pushed through the glass tube. If the blood contains the antibodies characteristic of a particular kind of disease, those antibodies will bind to the antigens inside the tube just as they do in the body. Those bound antibodies will partially clog the tube, blocking the current flowing through it. The resulting drop in the current flow will indicate that the blood contains signs of the disease.

What other diseases do you think the Nano-Transistor could help detect? We want to hear from you...

Majumdar, also an investigator with the Center for Information Technology Research in the Interest of Society (CITRIS), and his colleagues are currently working to demonstrate the ability of their nanofluidic transistor to detect prostate cancer, an effort sponsored by the National Cancer Institute. The transistor's diminutive size also means that an array of the tubes could be integrated into one small device to quickly screen for a variety of diseases without the burden of expensive and bulky laboratory equipment.

"I call it picoliter biology because the volume of a human cell is on the order of one picoliter," Majumdar says. "The question at the end of the day is can we use this technology to analyze a single human cell?"

Arun Majumdar's home page

Peidong Yang Research Group

Center for Information Technology Research in the Interest of Society

Lab Notes is published online by the Public Affairs Office of the UC Berkeley College of Engineering. The Lab Notes mission is to illuminate groundbreaking research underway today at the College of Engineering that will dramatically change our lives tomorrow.

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© 2003 UC Regents. Updated 10/31/03.