Source: MIT Review (www.technologyreview.com)
Author: Brittany Sauser

An ultrasensitive optical protein sensor analyzes saliva.

For the first time, an optical sensor, developed by researchers at the University of California, Los Angeles (UCLA), can measure proteins in saliva that are linked to oral cancer. The device is highly sensitive, allowing doctors and dentists to detect the disease early, when patient survival rates are high.

The researchers are currently working with the National Institute of Health (NIH) to push the technology to clinical tests so that it can be developed into a device that can be used in dentists’ offices. Chih-Ming Ho, a scientist at UCLA and principal investigator for the sensor, says that it is a versatile instrument and can be used to detect other disease-specific biomarkers.

When oral cancer is identified in its early stages, patient survival rate is almost 90 percent, compared with 50 percent when the disease is advanced, says Carter Van Waes, chief of head and neck surgery at the National Institute on Deafness and Other Communication Disorders (NIDCD). The American Cancer Society estimates that there will be 35,310 new cases of oral cancer in the United States in 2008. Early forms are hard to detect just by visual examination of the mouth, says Van Waes, so physicians either have to perform a biopsy–remove tissue for testing–or analyze proteins in blood.

Detecting cancer biomarkers in saliva would be a much easier test to perform, but it is also technically more challenging: protein markers are harder to spot in saliva than in blood. To create the ultrasensitive sensor, researchers started with a glass substrate coated with a protein called streptavidin that enables other biomolecules to bind to the substrate and to one another. The researchers then added a molecule that would catch and bind the cancer biomarker–a protein in saliva called IL-8 that previous research has proved to be related to oral cancer. They also added molecules designed to keep the glass surface free of other proteins that might muddy detection of the biomarker. To visualize the target molecules, Ho’s team then added a set of fluorescently tagged proteins designed to attach to the captured IL-8 markers.

Because saliva has a lower concentration of proteins than blood does, the team needed a highly sensitive method to detect the tagged proteins among the background noise, stray molecules in saliva that also fluoresce. So the researchers used a confocal microscope–an imaging system that employs a laser to collect the light generated from a sample–to analyze the saliva. Ho and his team found that focusing the laser light on a specific part of the sample resulted in a lower signal-to-noise ratio, allowing them to detect lower concentrations of the cancer biomarker.

Indeed, Ho says, the device is 100 times more sensitive than the standard protein-detection technique, ELISA. A more extensive and invasive process, ELISA requires that the proteins be purified from the blood before testing.

“The confocal microscope is a sophisticated imaging system at the heart of the UCLA researchers’ work and what ultimately led to the improvement in detection,” says John McDevitt, a professor of chemistry at the University of Texas, who is also working in salivary diagnostics. The main challenge now facing the UCLA group is how to use this technique outside a laboratory setting, he says.

The UCLA researchers tested the optical protein sensor on 40 patients–20 healthy subjects and 20 individuals with oral cancer. The results proved 95 percent accurate, says Ho. The study was published online in the international journal Biosensors and Bioelectronics.

“The new sensor is a major step in salivary diagnostics, an area that is being looked at very carefully to see where it might be better to use saliva than blood,” says Spencer Redding, chair of the department of dental diagnostic science at the University of Texas Health Science Center, in San Antonio, who is working with McDevitt. Other possible applications of such technology include detection of heart disease, infectious disease, and asthma, Redding says.