New device measure glucose concentration in saliva

New device to measure glucose concentration in saliva

4:04 AM, 27th January 2012
New device to measure glucose concentration in saliva
Each plasmonic interferometre consists of a slit flanked by two grooves etched in a silver metal film. The schematic shows glucose molecules “dancing” on the sensor surface illuminated by light with different colours.

RHODE ISLAND, US: Engineers at Brown University have designed a biological device that can measure glucose concentrations in human saliva. The technique could eliminate the need for diabetics to draw blood to check their glucose levels. The biochip uses plasmonic interferometre and could be used to measure a range of biological and environmental substances. 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 interferometre onto a fingernail-size biochip and measured the concentration of glucose molecules in water on the chip. 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. “This is proof of concept that plasmonic interferometre can be used to detect molecules in low concentrations, using a footprint that is ten times smaller than a human hair. The technique can be used to detect other chemicals or substances, from anthrax to biological compounds,” said Domenico Pacifici, Assistant Professor, Brown University

To create the sensor, the researchers carved a slit about 100 nanometre wide and etched two 200 nanometre-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.

These surface plasmon waves move along the sensor’s surface until they encounter the photons in the slit, much like two ocean waves coming from different directions and colliding with each other. 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 turns 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,” said Pacifici. The engineers learned they could vary the phase shift for an interferometre by changing the distance between the grooves and the slit, meaning they could tune the interference generated by the waves. The researchers could tune the thousands of interferometre to establish baselines, which could then be used to accurately measure concentrations of glucose in water as low as 0.36 milligrams per decilitre.

“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 Pacifici. The engineer’s next plan to build sensors tailored for glucose and for other substances to further test the devices. “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,” said Pacifici.

© Brown University News

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