Inorganic lanthanide nanoprobes for background-free luminescent bioassays

Luminescent bioassay techniques have been widely adopted in a variety of research and medical institutions. However, conventional luminescent bioassays utilizing traditional bioprobes like organic dyes and quantum dots often suffer from the interference of background noise from scattered lights and autofluorescence from biological matrices. To eliminate this disadvantage, the use of inorganic lanthanide (Ln3+)-doped nanoparticles (NPs) is an excellent option in view of their superior optical properties, such as the long-lived downshifting luminescence, near-infrared triggered anti-Stokes upconverting luminescence and excitation-free persistent luminescence. In this review, we summarize the latest advances in the development of inorganic Ln3+-doped NPs as sensitive luminescent bioprobes from their fundamental physicochemical properties to biodetection, including the chemical synthesis, surface functionalization, optical properties and their promising applications for back-ground-free luminescent bioassays. Future efforts and prospects towards this rapidly growing field are also proposed.