April 23, 2007

Lab-on-a-Chip Spots Potential Disease in Saliva

Photo of female scientist using pipette to transfer liquid samples to small containers in a tray Researcher prepares human saliva samples for analysis by Sandia's lab-on-a-chip deviceRandy Wong, Sandia National Laboratories.

A hand-held device that quickly analyzes saliva droplets for tiny amounts of a protein has shown promise as a potential diagnostic tool, according to a small clinical test. This type of device may eventually be used in the dentist’s or doctor’s office to aid in the detection and assessment of disease in the mouth—and possibly elsewhere in the body.

The device was created and evaluated by researchers at Sandia National Laboratories in Livermore, California. It is one of several saliva-based diagnostic tools now being developed with support from the NIH National Institute of Dental and Craniofacial Research (NIDCR). As reported in the March 27, 2007, issue of the Proceedings of the National Academy of Sciences, the scientists found that their device could reliably analyze a small amount of human saliva and measure concentrations of MMP-8, an enzyme associated with the chronic gum disease periodontitis.

To make their diagnostic test highly compact, the researchers created a "lab-on-a-chip"about twice the size of a stick of chewing gum. The miniature lab contains networks of tiny channels and chambers that filter and process the saliva to automatically detect and measure MMP-8 levels.

To test their device, the researchers collected saliva from 23 people—14 with periodontitis and 9 in good oral health. For each test, the researchers loaded about one-tenth of a drop of saliva into the system for analysis. The samples were processed in less than 5 minutes. On average, the study showed, those with good oral health had lower concentrations of MMP-8, while people with periodontitis had elevated levels of the tissue-damaging enzyme.

Saliva has several possible advantages as a diagnostic fluid, notes senior author Dr. Anup K. Singh, a chemical engineer at Sandia. It can be easily collected, doesn’t involve painful needle sticks, and saliva tests may eventually cost less than diagnostic blood tests. However, future saliva tests to detect compounds normally tested in blood will have to be considerably more sensitive than the equivalent blood test.

“Saliva is a mirror of blood, but … it’s not an exact mirror,” Singh said. “Everything that is present in blood is present in saliva but at concentrations 1,000 to 10,000 times lower.”

Nevertheless, this study proves the principle that lab-on-a-chip tests can detect proteins in saliva. Although this study searched for only one protein associated with periodontal disease, the Sandia device is flexible enough to detect other proteins as well. The researchers are now working to expand the system to search for many different molecules simultaneously.

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