Biochip enables glucose level measurement from human saliva

In order to check their glucose levels, diabetics usually have to draw blood. In order to eliminate the need for this invasive way of glucose level control, engineers at Brown University have designed a biological device that can measure glucose concentrations in human saliva. The technique takes advantage of a convergence of nanotechnology and surface plasmonics, which explores the interaction of electrons and photons (light).

The engineers at Brown etched thousands of plasmonic interferometers onto a fingernail-size biochip and measured the concentration of glucose molecules in water on the chip. They carved a slit about 100 nanometers wide and etched two 200 nanometer-wide grooves on either side of the slit. The slit captures incoming photons and confines them. The grooves, meanwhile, scatter the incoming photons, which interact with the free electrons bounding around on the sensor’s metal surface.

Those free electron-photon interactions create a surface plasmon polariton – a special wave with a wavelength that is narrower than a photon in free space. Plasmon polaritons move along the sensor’s surface until they encounter the photons in the slit, and “interference” between the two waves determines maxima and minima in the light intensity transmitted through the slit. The presence of an analyte (the chemical being measured) on the sensor surface leads to change in light intensity which can be measured in real time.

Their results showed that the specially designed biochip could detect glucose levels similar to the levels found in human saliva. Glucose in human saliva is typically about 100 times less concentrated than in the blood. By varying the phase shift for an interferometer by changing the distance between the grooves and the slit, the researchers could tune the thousands of interferometers in order to increase the accuracy of measurements.

“It could be possible to use these biochips to carry out the screening of multiple biomarkers for individual patients, all at once and in parallel, with unprecedented sensitivity”, said Domenico Pacifici, assistant professor of engineering at Brown University. “The proposed approach will enable very high throughput detection of environmentally and biologically relevant analytes in an extremely compact design. We can do it with a sensitivity that rivals modern technologies.”

The biochip could be used to measure a range of biological and environmental substances, from anthrax to biological compounds, in parallel on the same chip.

For more information, read the paper published in Nano Letters, a journal of the American Chemical Society: “Nanoscale Plasmonic Interferometers for Multispectral, High-Throughput Biochemical Sensing”.