NEW ORLEANS - Nanoscale electronics experts are often streaked to manufacture circuits Microchip companies already make millions of times better. But at the meeting of the American Chemical Society here yesterday, researchers described a nanoscale device that does something fleas can not touch: tracking proteins indicative of two different forms of cancer. On the road, the tables of these sensors could enable doctors to instantly screen patients for various diseases.
Researchers have been experimenting with electronic diagnostics for years, but with mixed success. The detectors typically use field-effect transistors (FET) devices in which a voltage applied to an electrode, called the gate, alters the current flow between two electrodes. For diagnosis, researchers have generally replace the gate of a material coated with proteins or other compounds to capture molecules of interest. As the captured molecules are charged, their presence alters the conductance between the two electrodes of the transistor. But although these devices operate frequently, they are generally not very sensitive, because they require a large number of target molecules to bind.
Hoping to improve the sensitivity, chemist Charles Lieber of Harvard University and his students have tried the same configuration with nanoscale transistors. Lieber's group has made these transistors for years, typically using son as small as 1 to 2 nanometers in silicon. For this study, they have shaped silicon nanowires doors coated with antibodies to the specific antigen of the prostate (PSA), prostate cancer marker. They then positioned the transistors in a patterned plastic pad with tiny channels which allowed fluid flow over them.
When the team injected a dilute solution containing PSA, the negatively charged protein bound to the antibody and modified conductivity FET, the graduate student Lieber Wayne Wang said at the meeting. In fact, he said, he and his colleagues managed to detect PSA at levels of 0,025 picograms per milliliter, making the detector more sensitive PSA yet created - over 100 times more sensitive than commercial PSA tests . Wang also noted that a similar sensor picked up the presence of CEA, a marker for colorectal cancer. And a simple array of nanosensors detected two cancer markers simultaneously.
"They did really good progress," said Liu Jie, a chemist at Duke University in Durham, North Carolina. "The question is, can they be made reliable and inexpensive manner in large quantities?" nanowire sensors, he said, still have a long way to go before reaching the market. But if successful, they could provide physicians instant playback of whether a patient has a wide variety of diseases.
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