Saliva and Tears an Indicator of Diabetes

Jonathan Claussen, a former Purdue University doctoral student who currently works as a research scientist at the U.S. Naval Research Laboratory stated that, "It's an inherently non-invasive way to estimate glucose content in the body." "Because it can detect glucose in the saliva and tears, it's a platform that might eventually help to eliminate or reduce the frequency of using pinpricks for diabetes testing. We are proving its functionality."

"Most sensors typically measure glucose in blood," noted co-lead researcher Claussen in the statement. "Many in the literature aren't able to detect glucose in tears and the saliva. What's unique is that we can sense in four different human serums: the saliva, blood, tears and urine. And that hasn't been shown before."

The sensor is composed of three main parts, including platinum nanoparticles, the enzyme glucose oxidase, and layers of nanosheets made up of a material of single-atom-thick film of carbon called graphene. The layers of nanosheets look like small rose petals and each petal has a couple of layers of stacked graphene. The ends of the petals have incomplete chemical bonds that defect where the platinum nanoparticles can be fastened. Electrodes are created by mixing nanosheet petals with platinum nanoparticles. The glucose oxidase then fastens to the platinum nanoparticles and the enzyme is able to convert glucose to peroxide, which produces a signal found on the electrode.

The researchers believe that the biosensor could be used for diabetes testing and examining medical conditions of a number of chemical compounds.

"Because we used the enzyme glucose oxidase in this work, it's geared for diabetes," continued Claussen in the statement. "But we could just swap out that enzyme with, for example, glutemate oxidase, to measure the neurotransmitter glutamate to test for Parkinson's and Alzheimer's, or ethanol oxidase to monitor alcohol levels for a breathalyzer. It's very versatile, fast and portable."

The new technology can already detect a glucose concentration more sensitive than other electrochemical biosensors. The biosensor can detect glucose in concentrations that are as low as 0.3 micromolar. It is also able to sense the difference between glucose and signals from other compounds that might interfere with sensors like ascorbic acid, acetaminophen, and uric acid; these three, in particular, are usually found in the blood and are electroactive, meaning they can generate an electrical signal without the help of an enzyme. Glucose normally has to react with the enzyme glucose oxidase before it can produce a signal.

"These are the first findings to report such a low sensing limit and, at the same time, such a wide sensing range," concluded Claussen in the statement.

Advanced Functional Materials, Aug. 2012