In order to measure their blood glucose levels, most diabetics must perform painful finger-prick tests on a daily basis. Hopefully, however, that may not always be the case. Scientists at Rhode Island's Brown University are now developing a biochip, that could someday be used to assess the concentration of glucose molecules in a tiny sample of saliva.

At the heart of the biochip technology is a miniscule device known as a plasmonic interferometer, which consists of a slit flanked on either side by single parallel grooves, all three etched into a silver film. There are thousands of these interferometers on the fingernail-sized piece of biochip material that the Brown researchers have created for their research.


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When light is shone through a liquid placed on a plasmonic interferometer, some of the photons are captured within the 100 nanometer-wide slit. Other photons are scattered by the two 200 nanometer-wide grooves and proceed to interact with the free electrons moving about on the silver's surface. These interactions result in surface plasmon polaritons, which are waves possessing a wavelength that is narrower than that of a photon in free space.

These waves move across the sensor's surface from the two grooves and when they meet with the photons trapped in the slit, interference occurs. The amount of interference varies depending on the concentration of a given element present in the liquid sample and also determines how much light is ultimately able to shine through the slit. By measuring the light intensity coming through each slit, the sensor is thus able to determine the concentration of that element.

By tweaking the distances between the grooves and the slits, the researchers have successfully detected glucose in water, in concentrations as low as 0.36 milligrams per deciliter (3.38 oz). This is similar to the levels found in human saliva, which are approximately 100 times lower than those in blood - conventional home testing devices aren't capable of detecting such low concentrations.

Once fully developed, the biochip could hopefully be used not only to measure glucose in blood, but also for the measurement of other biomarkers, or chemicals in the environment. One device could test for a number of elements simultaneously.

A paper on the Brown research was recently published in the journal Nano Letters.