February 2005

Synopsis: Nanotechnology

Continued from page 1

By Monya Baker (edit)

Super-sensitive Screen
Better virus detection through nanowires

Context: Health-care providers would benefit greatly from a ­simple, inexpensive method for determining whether a patient's runny nose or upset stomach signifies a virus -- or something else. A medi­cal lab can identify an infection from a tissue swab, but only after the time-consuming and expensive process of sample preparation and analysis.

Far better would be a device that could interact with a virus at the cellular level, producing an electrical signal that could be interpreted by computer chips and other electronics. Such a system would, in theory at least, be cheaper than existing diagnostic technolo­gies; it could also potentially screen numerous viruses at once and determine the presence or absence of any of them almost instantly. Silicon nanowires are one promising candidate as the detection technology, because they are about the same size as biological particles and could respond to their presence with great sensitivity.

Now, seminal work in the laboratories of Charles Lieber, a chemist and pioneer in the field of nanotechnology, and Xiaowei Zhuang at Harvard University has demonstrated that such a nanowire system can be built and can detect single virus particles -- a milestone in the development of a new generation of ultrasensitive nanosensors.

Methods and Results: Silicon nano­wires were "decorated" with virus-specific antibodies. When a virus bonded with one of the antibodies, the charged proteins on the virus's surface changed the nano­wire's conductivity, in much the way that an electrical charge can turn a transistor on or off. Viruses could be detected in seconds or minutes, and one type of virus would show up clearly even in the presence of another. The process worked even with samples that had not been extensively purified, though the researchers did not attempt to directly test samples of fluids such as plasma.

Why it Matters: The Harvard researchers' work is a breakthrough in the application of nanotechnology to the improvement of biosensors. The first use of such a virus detection system would likely come in a pharmaceutical laboratory: replacing the antibodies with potential drug molecules could help identify antiviral drugs. Such a system could make drug discovery faster and more efficient.

Outside of the lab, the technique could yield a simple biochip test that might be performed in any doctor's office, day care center, or private home. Of course, nano­wires are not necessarily the only means of building such a chip, and other technologies may yet prove to be more robust or less expensive. But the idea of selling a biochip every time a toddler sneezes is enough to ensure that, somewhere, a venture capitalist is smiling.

Source: Patolsky, F. et al. 2004. Electrical detection of single viruses. Proceedings of the National Academy of Sciences 101:14017-14022.