A new technique based on biochip detection of glucose in saliva instead of blood is likely to eliminate painful pricks for easy diabetes checks.

The new technique developed by Engineers at Brown University, Providence, RI, is based on a biological device that measures glucose concentrations in human saliva instead of blood.

The biochip uses plasmonic interferometers which have been designed to measure across various ranges of biological and environmental substances. Interferometer is a device that determines wave properties, measuring wave frequency, length or velocity.

The study, published in Nano Letters, a journal of the American Chemical Society, explained that the specially designed biochip could detect glucose levels similar to the levels found in human saliva. This is considered a feat as glucose in human saliva is almost 100 times less concentrated than in blood.  

This is proof of concept that plasmonic interferometers can be used to detect molecules in low concentrations, using a footprint that is ten times smaller than a human hair, said lead scientist Domenico Pacifici from the School Of Engineering at Brown University.

The study explained that the technique takes advantage of a convergence of nanotechnology and surface plasmonics, which explores the interaction of electrons and photons (light).

The study engineers at Brown fixed thousands of plasmonic interferometers onto a fingernail-size biochip and measured the concentration of glucose molecules in water on the chip.

Apart from diabetes testing, the device is seen to have future demand for detection of other chemicals such as anthrax or biological compounds.

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.

To create the sensor, the researchers engraved 100 nanometers-wide slit and etched two grooves which were 200 nanometer-wide on either side of the slit. The slit was created to capture incoming photons and confine them.

The grooves, meant to scatter the incoming photons, were designed to interact and bind with the free electrons on the sensor's metal surface. These free electron-photon interactions gave rise to surface plasmon polariton, a special wave with a wavelength that is narrower than a photon in free space.

These waves on further interactions with the photons in the slit along the sensor's surface behaved like two ocean waves coming from different directions and colliding with each other, explained the authors. The authors wrote that this interference between the two waves determined maxima and minima in the light intensity transmitted through the slit.

The presence of the chemical (glucose) which when measured on the sensor surface showed a variation in the relative phase difference between the two surface plasmon waves. This further caused a change in the light intensity, which the researchers measured in real time.

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

The scientists plan to improvise on the current technique by building sensors that could detect 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, Pacifici said.