Ultra-sensitive biosensor could assist early cancer detection

The 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,’ said Alam in a statement.

The device — dubbed a Flexure-FET biosensor — is said to combine 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 charged and uncharged biomolecules, allowing a broader range of applications than either type of sensor alone.

The sensor has two potential applications: personalised 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, said Alam.

The sensor’s mechanical part is a vibrating cantilever made from silicon. 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, for which a US patent application has been made, maximises sensitivity by putting both the cantilever and transistor in a ‘bias’. The cantilever is biased using an electric field to pull it downward.

The university said a key innovation is the elimination of the reference electrode, which is required for conventional electrical biosensors but cannot be miniaturised, limiting practical applications.

‘Eliminating the need for a reference electrode enables miniaturisation and makes it feasible for low-cost, point-of-care applications in doctors’ offices,’ said Alam.

Findings are detailed in a paper that appeared on 14 May in the Proceedings of the National Academy of Sciences. The paper was written by Purdue graduate student Ankit Jain, Alam and Pradeep R Nair, a former Purdue doctoral student who is now a faculty member at the Indian Institute of Technology, Bombay.