Silicon Nanowires Light Up For Imaging

Silicon nanowires can serve as intense in vitro and in vivo imaging probes, according to researchers at Purdue University (Nano Lett., DOI: 10.1021/nl901143p). Fluorescent compounds have long been used for biological imaging, but their optical response often weakens quickly when illuminated because of photobleaching. Nanoparticles, nanorods, and other nanoscale materials can partly sidestep the photobleaching problem, although in some cases most of the light used to excite fluorescence from those materials ends up heating and damaging the specimen. Now, Yookyung Jung, Ling Tong, Chen Yang, and coworkers at Purdue report that silicon nanowires outshine by a factor of 10 comparable-sized silver nanoparticles, which are considered a "gold" standard for intense nanosized emitters. In addition, the nanowires, which can be tailor-made synthetically, resist photobleaching after emission from silver nanoparticles grows dim. The researchers showed that when injected into a mouse, the nanowires—roughly 5 μm long and 40 nm in diameter—are visible in the animal's circulating blood and in tissue samples taken from the liver and spleen.