One of the most compelling promises of nanotechnology are tiny detectors that could instantly screen for hundreds of toxins or pathogens. Bundled into small handheld devices, these sensors could provide fast alerts of bioterror attacks. They could also be used to quickly and precisely detect early signs of cancer, before the disease turns deadly. (See “Drugstore Cancer Tests.”)
Now researchers at Yale University have developed ultrasensitive nanoscale sensors that are easy to manufacture. The sensors are based on semiconducting nanowires, which can detect single virus particles or ultra-low concentrations of a targeted substance, as other researchers have already shown. (See “Super-Sensitive Screen.”) Nanowire sensor devices have proven difficult to mass-produce, however. For one thing, the methods used to make them are typically incompatible with those used to make the electronics that amplify and process the signals the nanowires generate.
In the process developed by Mark Reed, a professor of electrical engineering and applied physics, and his colleagues, nanowire sensors can be produced by methods compatible with the high-throughput techniques of the semiconductor industry. Sensors produced this way could be integrated with the electronics needed to process data, potentially leading to compact and relatively affordable devices.
Such sensors could be much smaller than standard optical-based detectors and simpler to use. Because the sensors would be based on an electronic signal, target molecules would not have to be chemically tagged with fluorescent molecules and then observed through bulky optical readers. Thousands of sensors could be packed into a hand-held device, which could produce results almost instantaneously.
To make their sensors, Reed and his colleagues used a process similar to the one used to pattern computer chips.
The researchers begin with commercially available films of silicon on top of an insulating material; then they use conventional techniques to lay down patterns of lines called masks that will determine the location of the nanowires. Next, they etch away the silicon not covered by the masks. Though the masks are not thin enough to produce nanowires, the researchers allow the etching to continue eating away at the material under the edges of the mask, finishing the task. Using the process, the researchers were able to make multiple nano sensors on the same chip.
In experiments described in this week’s issue of the journal Nature, the sensors were used to detect a variety of things, including specific antibodies. The nanowires are first spotted with molecules designed to bind to the target antibody; when the target is present and the link is made, it causes the conductivity in the nanowire to change, creating a readable signal. Since the body’s immune system produces minute amounts of antibodies in response to diseases such as cancer, the devices could be used for early diagnoses.
Although he will not specify when devices using the sensors will be available, Reed says it should be soon. “I work on a lot of things that I’ll never see in my lifetime,” he says. “This will happen in my lifetime.”