title: Upconversion nanoparticles: synthesis, surface modification and biological applications.
abstract: New generation fluorophores, also termed upconversion nanoparticles (UCNPs), have the ability to convert near infrared radiations with lower energy into visible radiations with higher energy via a nonlinear optical process. Recently, these UCNPs have evolved as alternative fluorescent labels to traditional fluorophores, showing great potential for imaging and biodetection assays in both in vitro and in vivo applications. UCNPs exhibit unique luminescent properties, including high penetration depth into tissues, low background signals, large Stokes shifts, sharp emission bands, and high resistance to photobleaching, making UCNPs an attractive alternative source for overcoming current limitations in traditional fluorescent probes. In this article, we discuss the recent progress in the synthesis and surface modification of rare-earth doped UCNPs with a specific focus on their biological applications.
  
  
  BACKGROUND
  Upconversion nanoparticles - a new generation of fluorophores - convert near infrared radiations into visible radiations via a nonlinear optical process. These UCNPs have evolved as alternative fluorescent labels with great potential for imaging and biodetection assays in both in vitro and in vivo applications.
authors.affiliation: College of Sciences, Northeastern University, Shenyang, People's Republic of China.
authors.forename: Meng
authors.initials: M
authors.lastname: Wang
authors.forename: Gopal
authors.initials: G
authors.lastname: Abbineni
authors.forename: April
authors.initials: A
authors.lastname: Clevenger
authors.forename: Chuanbin
authors.initials: C
authors.lastname: Mao
authors.forename: Shukun
authors.initials: S
authors.lastname: Xu
mesh_terms: D000818:Animals; D003952:Diagnostic Imaging / Q000379:methods; D005456:Fluorescent Dyes / Q000737:chemistry*; D006801:Humans; D008674:Metals, Rare Earth / Q000737:chemistry*; D008856:Microscopy, Fluorescence / Q000379:methods; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D036103:Nanotechnology / Q000379:methods; D013499:Surface Properties
chemical_list: D005456:Fluorescent Dyes; D008674:Metals, Rare Earth