Researchers at the University of California, Los Angeles, report they have developed an ultrasensitive optical protein sensor that may aid in detecting disease-associated proteins in saliva, according to an article in the October issue of Biosensors and Bioelectronics.
The sensor can be integrated into a specially designed lab-on-a-chip, or microchip assay, and preprogrammed to bind a specific protein of interest, generating a sustained fluorescent signal as the molecules attach. A confocal microscope then reads the intensity of the fluorescent light, a measure of the protein’s cumulative concentration in the saliva sample. Scientists then gauge whether it corresponds with levels linked to developing disease.
The scientists—supported by the National Institute of Dental and Craniofacial Research, part of the National Institutes of Health—primed the optical protein sensor to detect the interleukin-8 (IL-8) protein, which, at a higher-than-normal concentration in saliva, is linked to oral cancer. They tested saliva samples from 20 people, half of whom were healthy and half of whom had been diagnosed with oral cancer. The sensor correctly distinguished between health and disease in all cases.
The sensor achieved a limit of detection for IL-8 that is roughly 100 times more sensitive than today’s blood-based enzyme-linked immunosorbent assay (ELISA), the standard technique for measuring protein in bodily fluid. The limit of detection refers to a sensor’s ability to distinguish the lowest concentration of a protein or another target molecule apart from competing background signals.
Winny Tan, PhD, a lead author, said the proof-of-principle tests of the sensor take between 30 minutes and one hour to complete. "About 90 percent of our time was spent in sample preparation, not actually performing the assay," she said. "With further integration and automation of the test, the time could be reduced significantly."
The laboratory previously developed a saliva-based electrochemical sensor, which binds the protein of interest by using an electrical sensor system. Chih-Ming Ho, PhD, a scientist and senior author, explained that the optical and electrochemical sensors have pros and cons.
"The optical sensor requires a more expensive setup because of the confocal microscope," said Dr. Ho. "So, in a small dental or [physician’s] office, the electrochemical sensor generally would be easier and cheaper to use. But to really push down the signal-to-noise ratio, the optical sensor has the advantage."
Dr. Ho said the optical sensor might be better suited to a more specialized central laboratory. "But the technology is advancing so rapidly," he explained, "it’s difficult to predict how the optical sensor might be used in the years to come."
