Nano-biosensor can detect molecules at femtomolar levels

A detector that is sensitive to just a few molecules of interest in a glass of water could find a use in diagnostics and forensics.

The nano-biosensor, based on a photonic crystal nanowire array, was developed by Yuerui Lu, a graduate student of electrical and computer engineering at Cornell University.

The experimental device is a mechanical resonator, 50 microns in diameter, made of a thin silicon/silicon dioxide membrane with ordered, tightly packed vertical nanowires on top. The design achieves a high surface-to-volume ratio for biomolecule detection, which means it can detect molecules at femtomolar concentrations.

The sensor works by attaching single-stranded probe DNA molecules onto the nanowires. When those molecules come into contact with a target single-stranded DNA, the relevant molecules bind together, changing the mass detected by the device. The mass change causes a change in the resonance frequency of the device.

A laser beam shines on the device and the nanowires’ design allows for more than 90 per cent absorption of the light, resulting in an efficient opto-thermo-mechanical excitation of the resonator.

An optical readout of the resonance frequency change can be accomplished remotely, quickly and free of electrical wires, making the device convenient and inexpensive to make, the researchers said.

The new device could instead be coded with particular DNA sequences of relevance and those specific molecules could be detected in early stages, when concentrations are low.

‘You could have a cartridge with an array of the membrane sensors and quickly scan to see what DNA imperfection you might have,’ Lu said. ‘Whereas today’s tests take time and are expensive.’