Ultrasensitive Biosensor Promising for Medical Diagnostics

May 17, 2012 by Journal of Analytical and Bioanalytical Techniques

he device, which could be several hundred times more sensitive than other biosensors, combines the attributes of two distinctly different types of sensors, said Muhammad A. Alam, a Purdue University professor of electrical and computer engineering. “Individually, both of these types of biosensors have limited sensitivity, but when you combine the two you get something that is better than either.”

The device — called a Flexure-FET biosensor — combines a mechanical sensor, which identifies a biomolecule based on its mass or size, with an electrical sensor that identifies molecules based on their electrical charge. The new sensor detects both charged and uncharged biomolecules, allowing a broader range of applications than either type of sensor alone.

The sensor has two potential applications: personalized medicine, in which an inventory of proteins and DNA is recorded for individual patients to make more precise diagnostics and treatment decisions; and the early detection of cancer and other diseases.

In early cancer diagnostics, the sensor makes possible the detection of small quantities of DNA fragments and proteins deformed by cancer long before the disease is visible through imaging or other methods, Alam said.

The sensor’s mechanical part is a vibrating cantilever, a sliver of silicon that resembles a tiny diving board. Located under the cantilever is a transistor, which is the sensor’s electrical part.

In other mechanical biosensors, a laser measures the vibrating frequency or deflection of the cantilever, which changes depending on what type of biomolecule lands on the cantilever. Instead of using a laser, the new sensor uses the transistor to measure the vibration or deflection.

The sensor maximizes sensitivity by putting both the cantilever and transistor in a “bias.” The cantilever is biased using an electric field to pull it downward as though with an invisible string.