Salivary Diagnostic Device Shows Promise
News Apr 12, 2007
Researchers supported by the National Institute of Dental and Craniofacial Research (NIDCR), part of the National Institutes of Health, have engineered a portable, phone-sized test that in minutes measures proteins in saliva that may indicate a developing disease in the mouth or possibly elsewhere in the body.
According to researchers, the point-of-care test one day in the future could become a common sight in the dentist’s office. As envisioned by the researchers, a dentist would collect a small saliva sample with a patient’s consent, load it into the diagnostic cartridge, start the assay, and have a read out waiting after a cleaning or a dental procedure has been completed.
Called IMPOD, the device is described in the March 27 issue of the Proceedings of the National Academy of Sciences. In the report, the scientists offer the results of proof of principle experiments in which IMPOD reliably measured the concentrations of MMP-8, an enzyme associated with chronic inflammation of the gums called periodontitis.
“The IMPOD is designed to measure up to 20 analytes, or biochemicals, at once,” said Dr. Anup Singh, a chemical engineer at the Sandia National Laboratories in Livermore, Cal. and senior author on the paper. “We haven’t scaled up to that point, but we are doing multi-analyte analyses in the laboratory. Our greatest need right now is validated biomarkers to enable further clinical studies. The basic engineering of the device has been completed.”
According to Singh, he and his colleagues were intrigued a few years ago by the many potential advantages of saliva as a diagnostic fluid. These include easy collection, no painful needle sticks, portability of the tests, and potentially a lower cost to patients than blood assays.
But they were initially daunted by the research task at hand. “Saliva is a mirror of blood, but with a caveat, said Singh. “It’s not an exact mirror, meaning everything that is present in blood is present in saliva but at concentrations 1,000 to 10,000 times lower. It’s diluted by saliva and the other secretions in the mouth. So we needed sensitivity 1,000 to 10,000 times better than we’d need if we were screening serum samples.” Sensitivity refers to the lowest amount of an analyte that a test can detect.
“The bound proteins stack against the membrane because they are too big to squeeze through the pores,” said Amy Herr, also at Sandia National Laboratories and lead author on the paper. “Conversely, the many smaller molecules in saliva flow right through the pores and are filtered out and routed to a waste chamber.”
To put their lab on a chip to the test, the research team collected saliva from 23 people — 14 with periodontitis and nine in good oral health. Loading roughly one-tenth of a drop of saliva for analysis, the IMPOD processed the samples and produced a result in less than five minutes.
The results showed that on average those in good oral health had lower concentrations of MMP, while people with periodontitis on average had elevated levels of the tissue-damaging enzyme. The results were confirmed with a standard ELISA blood test, currently the gold standard.
“The data correlate nicely with those from other types of studies that show that MMP-8 is indicative of periodontitis,” said Dr. William Giannobile, a researcher at the University of Michigan School of Dentistry in Ann Arbor.
“There is every reason to believe additional biomarkers for periodontitis can be identified, as the work to catalogue salivary genes and proteins nears completion and our understanding of periodontal disease continues to advance,” he said.
The researchers noted that IMPOD, although developed for saliva, could be used to test other diagnostic fluids such as blood and urine.