Nanoparticle-based tumor detection schemes often rely on injecting particles that seek out and stick to cancer cells. In order to see where they found their target, light, usually in the near-infrared range, is used to excite and fluoresce the nanoparticles. The limitation with this is that near-infrared light doesn’t penetrate soft tissue deep enough to find tumor sites more than a few millimeters below the surface. Shortwave infrared, a spectrum of light invisible to the human eye having wavelengths between 0.9 and 1.7 microns, can transit through a lot more tissue before fading away, but the fluorescent dyes that it is able to excite have either been too toxic or just don’t provide the image quality to accurately define the margins of tumors.
Researchers at Rutgers University are now using rare-earth nanocrystals, which are not as rare as was commonly believed, to fluoresce to shortwave infrared. Since rare-earths can still be toxic, the nanoparticles are surrounded by human serum albumin for safe passage through the body. These nanoparticles tend to collect around areas of disease and are excitable with shortwave infrared. Since different rare-earths glow at different colors when excited, using combinations of these metals can allow for wide-spectrum detectors of cancer. The researchers have shown that, at least in mice, they were able to spot cancer earlier than using more traditional near-infrared or MR imaging.