Ultrasensitive Biosensor Detects Cancer

The device, which could be several hundred times more sensitive than other biosensors, combines the attributes of two distinctly different types of sensors, a mechanical sensor, which identifies a biomolecule based on its mass or size, and an electrical sensor that identifies molecules based on their electrical charge.

At Purdue University (West Lafayette, IN, USA) scientists found that the new sensor detects both charged and uncharged biomolecules, allowing a broader range of applications than either type of sensor alone. 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. 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.

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. 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. The device is called a Flexure-field effect transistor (FET) biosensor. A key innovation is the elimination of a component called a reference electrode, which is required for conventional electrical biosensors, but cannot be miniaturized, limiting practical applications.

The authors concluded that there are broad ranges of applications that can benefit from the sensitivity gain of the biosensor. For example, the current genome sequencing schemes require polymerase chain reaction (PCR) amplification of DNA strands because of the lower sensitivity of existing biosensors. The high sensitivity of Flexure-FET can eliminate the requirement of multiplication step and hence reduce the cost of sequencing. The study was published on May 23 2012, in the Proceedings of the National Academy of Sciences of the United States of America.

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