HANCOCK, N.H. Chemistry, physics and nanoscale electronics are being blended to create novel biomedical devices at Harvard University's Department of Chemistry and Chemical biology. The research is not only opening up insights into nanoscale electronic devices, recent results also suggest that fundamentally new types of molecular sensors could be in the offing.
At the recent annual meeting of the American Chemical Society a member of Charles Lieber's group of physical chemists at Harvard described a chemically-gated nanoscale transistor that might signal the start of a new approach to medical diagnostics. The transistor was built on a silicon nanowire and the gate was coated with antibodies created by the immune system in response to prostate cancer.
The transistor then registers the presence of the complementary protein antigen in the blood when it binds to the antibody. The electrical characteristics of the gate of the nanoFET are altered by the bound protein, creating a signal. Sensors based on the chemical nanoFET are able to register far smaller concentrations of the antigen than any other currently known methods.
The Lieber group has been looking at a wide variety of nanowire systemsdevices using carbon nanotubes, silicon and compound semiconductor nanowires have been created for different applications. One promising line of research has been the creation of a nanoscale memory architecture using carbon nanotubes. The device consists simply of two arrays of nanotubes at right angles, one suspended over the other.
Two nanotubes that cross over one another can have two stable mechanical states. Elasticity tends to keep them apart, but if forced into contact by putting electrical charge on the wires, molecular forces will keep them in contact when the current is switched off.
While in contact, the electrical resistance of the junction is much lower than in the suspended configuration, making it easy to electronically sense the state of the crossed wires. A simplifying aspect of this scheme is the fact that the memory devices themselves are identical with the interconnect and the system is self-registeringa memory element will appear wherever the wires happen to intersect.
The researchers are also working on a variety of atomic force and chemical force probes that could be used to measure or manipulate molecular electronic systems. In one project, a chemical vapor deposition technique was used to grow carbon nanotubes on silicon atomic force microscope tips in a bid to create a mass-production technique for ultra-precise nanotube tips.
More on the lab's activities can be found at The Lieber Group web site.