February 27, 2006
Transistor-Cantilever Combo Detects Biomolecules With High Sensitivity
Microcantilevers, tiny devices that resemble a diving board, show great promise for detecting rare disease-related molecules that might be present in biological samples. Indeed, researchers have developed several prototype devices that measure the nanoscale bending that occurs when such a molecule binds to an antibody or complementary nucleic acid sequence attached to the cantilevers (click here to see earlier stories). In most cases, these devices have successfully used lasers and other optical systems to measure cantilever bending, but such optical methods are likely to be difficult to manufacture and have limited use with turbid or opaque biological samples.
To get around these potential limitations, a team led by Vinayak Dravid, Ph.D., and Gajendra Shekhawat, Ph.D., colleagues at Northwestern University, coupled a microcantilever with a metal-oxide semiconductor field-effect transistor, or MOSFET, to yield a device that generates a direct electrical signal whenever the cantilever bends in response to biomolecule binding. This new device, note the researchers, can be mass-produced using standard computer chip design and manufacturing techniques. The results of this effort will appear in the journal Science.
In order to create a device with the greatest sensitivity, the investigators embedded the MOSFET in part of a gold-coated silicon nitride microcantilever that undergoes the greatest stress during bending. In this way, any bending produces a sharp change in electrical current flowing through the transistor. Indeed, this device was capable of detecting bending of as little as five nanometers, which was more than sufficient to reliably detect binding of DNA, antibodies, and prostate specific antigen (PSA) to the microcantilevers.
“We believe our work ushers a new era in biochemical sensing, wherein emerging bio-nano-structures can now be integrated on established engineering platforms such as CMOS and MOSFET,” wrote Vinayak in a note to Cancer Nanotech News. “We are excited by the prospects that MOSFET-embedded microcantilever approach may open up new vistas in biochemical sensing via high sensitivity, on-chip electronic detection that is amenable to massively parallel, multiplexed and remotely addressable networked systems.”
This work is detailed in a paper titled, “MOSFET-embedded microcantilevers for measuring deflection in biomolecular sensors.” Vinayak is a contributing member of the Nanomaterials for Cancer Diagnostics and Therapeutics Center for Cancer Nanotechnology Excellence at Northwestern University. This paper was published online in advance of print publication. An abstract is available through PubMed.
Integrating a transistor at the base of a gold, receptor-coated microcantilever yields a device capable of detecting small numbers of rare cancer-related molecules in biospecimens. The cantilever-transistor combo generates a sharp electrical signal upon biomolecule binding without the need for laser-based optics or other measuring technologies. Image courtesy of Soo-Hyun Tark and Vinayak P. Dravid.