Sensor checks blood sugar levels by measuring saliva

Researchers at Brown University are working on a sensor that can check blood sugar levels by measuring glucose concentrations in saliva, rather than in blood.

According to a statement, the technique takes advantage of a convergence of nanotechnology and surface plasmonics, which explores the interaction of electrons and photons.


Their results showed that the 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.

‘This is proof of concept that plasmonic interferometers can be used to detect molecules in low concentrations, using a footprint that is 10 times smaller than a human hair,’ said Domenico Pacifici, assistant professor of engineering and lead author of a paper on the research published in Nano Letters.

The technique can be used to detect other chemicals or substances, from anthrax to biological compounds, Pacifici said, and detect them at once, in parallel, using the same chip.

To create the sensor, the researchers carved a slit about 100nm wide and etched two 200nm-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 on the sensor’s metal surface.


These surface plasmon waves move along the sensor’s surface until they encounter the photons in the slit. This ‘interference’ between the two waves determines maxima and minima in the light intensity transmitted through the slit.

The presence of an analyte on the sensor surface generates a change in the relative phase difference between the two surface plasmon waves, which in turn causes a change in light intensity — measured by the researchers in real time.

‘The slit is acting as a mixer for the three beams — the incident light and the surface plasmon waves,’ Pacifici said.


‘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,’ Pacifici said.
