Fluorescent probes based on upconverting lanthanide nanostructures

Lanthanides (or rare-earth elements) usually appear as an appendage of the periodic table, but in recent years they are being used in an evergrowing variety of applications in modern nanotechnology and nanomedicine. In particular, lanthanide-doped solids show unconventional anti-Stokes emissions, due to their ability to convert near infrared (NIR) radiation into shorter wavelengths, such as visible light through a process known as photon upconversion. As a consequence, the last decade has seen a growing interest in the production of lanthanidedoped upconverting nanocrystals. They have been developed as a new type of promising luminescent tool for applications in biological assays and medical imaging, as an alternative to usual organic fluorophores and quantum dots. These NIR fluorescent probes have a weak fluorescence background, long temporal resolution, and high resistance to photobleaching, and are able to absorb NIR light which has high tissue penetration power. These features, as well as their synthesis, their coating strategies, and the biological applications of upconverting nanoparticles will be fully discussed in this chapter.© 2013 Nova Science Publishers, Inc. All rights reserved.