Lanthanides: Upconversion Nanoparticles for Bioimaging Applications

Abstract

Stimulated by the prevalence of nanotechnology since the late 1990s, lanthanide-doped upconversion nanoparticles (UCNPs) have attracted enormous attention in biological sciences, especially for bioimaging. Compared with conventional bioimaging fluorophores, UCNPs possess unique upconversion luminescence features, high resistance to photobleaching, good chemical stability, and tolerable toxicity. Thus, UCNPs are considered to be very promising near-infrared bioimaging agents with the characteristics of high signal-to-noise contrast and high penetration depth. This chapter begins with an introduction to upconversion mechanisms and upconversion materials, followed by the synthesis and chemical surface modifications of UCNPs. The biological applications of UCNPs, focusing on in vivo imaging, are discussed. And lastly, the prospects of UCNPs for biological applications are also addressed.