Lanthanide‐Based Luminescence for Medical Diagnostic and Imaging

Abstract The need for accurate and, possibly, real‐time medical imaging is growing substantially, particularly in view of the development of personalized medicine, image‐guided surgery, and theranostics. These needs include not only morphologic evidence but also crucial metabolic information that can only be gained if single‐molecule imaging and tracking can effectively be achieved. Important parameters are sensitivity, resolution, penetration depth, ease of implementation and processing, and cost. Among the various techniques developed to date, such as X‐ray imaging, magnetic resonance imaging, computed tomography, proton emission tomography, or scintigraphy, each has specific advantages, but none meets all the desired criteria. Optical imaging is filling some gaps, particularly with respect to resolution and ease of implementation. The scope of this article narrows down to lanthanide‐based luminescence imaging taking advantage of specific properties of 4f–4f transitions: narrow bands, large induced Stokes shifts, long lifetime, and little sensitivity to the chemical environment of the bioprobe. Challenges in luminescence microscopy and nanoscopy are first discussed before focusing on lanthanide chelates in highly selective and sensitive immunoassays, in vitro and in vivo bioimaging, and theranostics with photodynamic treatment of cancer being highlighted. Next, the various aspects of lanthanide inorganic nanoparticles as bioprobes are overviewed, exemplifying the advantages they have over other probes. Upconversion, persistent luminescence, and dye‐sensitized nanoparticles are highly attractive, and their incorporation into complex biological systems is instrumental for imaging, drug delivery, and monitoring that are essential aspects of biomedicine.