Doctors could soon be able to screen for various cancers using a silicon device that detects the presence of proteins and similar species in bodily fluids. Existing screening techniques involve complex, unpleasant procedures such as barium meals and enemas.

Unlike cantilever-type MEMS that have been used to weigh biological samples, the device being developed by researchers at the University of Newcastle is self-referencing, and needs minimal temperature control to ensure accuracy. The 100µm x 1µm diaphragm design is based on a silicon gyroscope previously developed by Professor Jim Burdess.

"If you have a structure that is essentially cyclically symmetric, then one of the properties of the structure is that it has two independent modes of vibration," said Burdess. "And if you make that structure perfectly, then those two independent modes have the same frequency."

The silicon diaphragm is affected by the mass of individual molecules

However, the manufacturing process cannot achieve perfection, so Burdess and his colleagues typically use laser ablation to tune the mass and bring the two modes into coincidence. It was a conversation with Professor Calum McNeil from the University’s School of Clinical and Laboratory Sciences that led to the imperfect gyroscope being pressed into service as a mass sensor.

"One of the advantages of this particular [device] configuration is that it has a certain common mode property," said Burdess. "So if you change any pre-tension in the sensor, which you could do through thermal changes, then those changes do not increase or decrease the modal split, they just move the two frequencies up and down. It’s sort of an inherent compensation."

To take advantage of that, Burdess and McNeil developed a process of opening up sectors on the device’s surface and chemically functionalising them to bind proteins. So when the diaphragm is vibrationally excited, any species sticking to its surface causes a change in the constant mode splitting that is indicative of the mass of the molecule.

"We’ve just started a [11-nation, €12m] programme of work funded by the EC," said Burdess. "There is more than one sensor in that project and the ultimate aim is to have a device at the point of care, and in doctors’ surgeries."

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