On-chip cavities to detect changes in refractive index and microscopic particles are being investigated by the University of Oxford.
A lab prototype can measure refractive index changes down to about 3×10-4, and work has started on one intended to detect 10-6.
“A similar approach allows detection of individual particulates passing through the sensor. It is thought that particles as small as 20nm can be measured, compatible with detection of water-borne viruses and particulates,” said Isis Innovation, the intellectual property arm of the University, which is looking for licensees.
In the device, Bragg mirrors confine light in a cavity (see image, right) of the order of 1µm3 – about a cubic wavelength – through which analyte passes.
Mirrors and the cavity shape make the cavity optically resonant and “a range of straightforward optical techniques” can be used to make measurements, says Isis.
Researchers have sensed refractive index change due to glucose in aqueous solution using by measuring shift in mode resonance within 30 femtolitres of the cavity.
For parallel sensing, cavities can be fabricated in arrays, and they are compatible with microfluidic sample delivery.