Someday in the not too distant future patients may visit a doctor’s office, provide a sample of saliva or blood, and know in minutes if they are prone to heart disease, gum disease, or cancer. There would be no sending samples to off-site labs for analysis and waiting days to obtain the vital information.
A hand-held medical diagnostic device being developed at Sandia promises to be this ticket to better health for millions of Americans.
“We have taken technology that we’ve worked on for several years — the lab-on-a-chip devices — and are adapting them for use in medical diagnostics,” says Anup Singh (8321), project lead. “We’ve tested saliva samples from healthy patients for gum disease, and within the next few months we will begin using the diagnostic to test diseased samples.”
Lab-on-a-chip technologies were developed in the mid-1990s for detecting biotoxins and chemical agents. In new incarnations they are used in the analysis of bodily fluids, such as saliva and blood, for detecting certain diseases. Expanding on established microchip-based separation technologies, the research team adapted a method known as an immunoassay to a chip. The combination of the lab-on-a-chip technology and the immunoassay technique allows for fast and sensitive analysis of biomarkers specific to certain diseases.
As part of the immunoassay process, antibodies specific for biomarkers of interest, such as gum or heart disease, are tagged with a fluorescent dye and then mixed with a patient’s saliva or blood. Biomarkers present in the sample attach themselves to the fluorescent antibody. The mixture is injected into a microchip using a syringe. An applied electric field forces the sample to flow through a microchannel that is two to five centimeters long, tens of microns deep, and a few hundred microns wide
As the sample moves through the channel, cast-in-place porous polymers in the microchannel sort molecules based on their size and electrical charge. If biomarkers for the disease are present in the patient’s sample, the lab-on-a-chip analysis will separate fluorescent antibodies bound to the biomarker from unbound antibodies.
A photomultiplier tube then detects the fluorescence emission with extreme sensitivity. After quantifying the relative fluorescence of the two species — bound and unbound antibodies — researchers can determine the amount of biomarker present in the patient’s sample. If the sample contains significant fluorescence emission from a bound antibody, indicating that biomarkers are present above a certain level, a doctor could conclude that the patient has or will eventually get the disease for which he/she is being tested. At the conclusion of the test, still in the doctor’s office, preventive or therapeutic care could begin.
The entire device, including the channeled glass chips, photomultiplier, and electronics, will fit into a hand-held package that weighs less than five pounds.
“The beauty of this device is that it has everything required to make it useful — sensitivity, portability, and the ability to run tests quickly,” Anup says. “It is small and can be carried with ease almost everywhere. It’s also is very sensitive and works fast. Within a few minutes you can tell if you have a diseased sample.”
Using Sandia’s lab-on-a-chip technologies for medical diagnostic purposes grew out of a conversation Terry Michalske, newly named Director of Sandia’s Physical Chemical Biomolecular Science Center 8300, had with a National Institutes of Health (NIH) program director in 2001. The program director told Terry of a National Institute of Dental and Craniofacial Research (NIDCR) call for proposals to develop a new way of approaching oral diagnostics. Terry shared the information with Len Napolitano, Deputy Director of Biological and Microfluidic Sciences Center 8320, who told Anup and Victoria VanderNoot (8321), two researchers working on microfluidic projects. Anup and Victoria immediately saw how advantages inherent to lab-on-a-chip devices could be harnessed for medical purposes.
Having never worked with saliva samples, the Sandia researchers identified the need to partner with a dental researcher. With the help of Charlie Hasselbrink, an ex-Sandian and an engineering professor at the University of Michigan, a collaboration was established with Will Giannobile, an expert in gum disease and an associate professor at the University of Michigan School of Dentistry. The team also included Harold Craighead, a professor at Cornell University’s School of Applied and Engineering Physics, and Mark Burns, a professor at the University of Michigan’s School of Engineering.
The team, led by Sandia, sent a letter of intent to NIDCR, wrote the proposal, and obtained the funding in August 2001.
Pretty exciting stuff
“It was pretty exciting,” Anup says. “This was the first time Sandia was the lead institution on an NIH grant. I learned about being awarded the funding at 4 p.m. that August day in 2001, and by 5 p.m. our director, manager, and team members were in my office celebrating.”
The current research team at Sandia also includes Amy Herr and Anson Hatch (both hired in 8321 to work on the project), Dan Throckmorton (8321), and Ron Renzi (8755). Amy and Dan lead the immunoassay development; Anson is working on preconcentration and multiplexing; and Ron is responsible for all aspects related to device engineering.
Much of the research is centered on detection of gum disease from a patient’s saliva and gingival crevicular fluid, the fluid between the tooth and gum. Early detection of gum disease is of significant interest to the medical community. Some 20-45 million Americans suffer from gum disease and more than $2 billion a year is spent to diagnose and treat it.
Working with saliva
“Saliva is a mirror of blood,” Anup says. “Everything in saliva exists in blood but at concentrations a hundred to a thousand times lower than blood.”
Saliva is already being used for detecting HIV and drugs-of-abuse in commercial instruments. Saliva makes sense as a patient sample; obtaining saliva is a noninvasive process that requires no needles and is much more tolerable than traditional blood taking. Anup anticipates that in the future saliva will be used to detect everything from gum disease to heart disease to cancer.
In addition to biomarkers for gum disease, Amy and Dan are also developing assays for cardiovascular disease markers such as C-Reactive protein.
Anup says that although the primary goal is to analyze saliva, “we have shown that our device can work with blood as well.” Having the ability to analyze multiple bodily fluids makes the device useful for a wide variety of clinical applications.
Having already studied saliva samples from healthy people, the Sandia researchers will begin studying samples from 50 to 100 diseased patients in January. The patients are being recruited by Giannobile at the University of Michigan.
“Working with samples from actual patients will give us the opportunity to see how accurate our immunoassay method is,” Anup says.