How sticky is snot? The rest of the world might not ask that question every day, but a group at the University of North Carolina does. They now have an answer, thanks to a laser-based imaging method, and it could enable doctors to monitor and better treat lung diseases. The imaging method uses a combination of nontoxic gold nanoparticles and light to measure the stickiness of mucus that lines a person’s airway and subsequently the lungs. In a recent study, the researchers placed gold-coated nanorods on the surface of mucus samples. By illuminating the samples with laser light, they could then track the rods’ diffusion into the mucus, allowing them to analyze the way light bounces off the nanoparticles. The slower the nanorods diffused, the thicker the mucus became. The new method demonstrated effective imaging even when the mucus was sliding over a layer of cells — this is typically challenging, as mucus inside the human body is usually in motion, the researchers said. In healthy adults, cilia (cell appendages) line the airways and extract mucus out of the lungs and into the throat. If the mucus becomes too viscous, it can become trapped in the lungs, making breathing more difficult, said physicist Dr. Amy Oldenburg. This essentially halts the removal of pathogens that typically cause chronic lung infections. There are numerous medications available to thin mucus, but monitoring the drugs’ effects on its viscosity inside the body has long been difficult. “The ability to monitor how well mucus-thinning treatments are working in real time may allow us to determine better treatments and tailor them for the individual,” Oldenburg said. The researchers are working toward clinical translation; the method could be especially useful for diseases such as cystic fibrosis and chronic obstructive pulmonary disease. They are also looking at how it could be adapted for testing on humans and used to directly enter the airway for further investigation of how mucus-flow properties differ throughout the body. The researchers will present their findings at The Optical Society's annual Frontiers in Optics meeting later this month. For more information, visit: www.unc.edu.