Recent Advances in Ultrasmall Fluorescent Nanoparticles for In vivo Biosensing

Monitoring the level and dynamics of biologically essential species in living organisms is significant for understanding cellular functions and diagnosing relevant diseases, thus the development of reliable in vivo detection methods is highly important. Ultrasmall-sized fluorescent nanoparticles have emerged as ideal sensing probes due to their easy preparation, distinct photophysical properties and good biocompatibility. This review summarizes recent advances in developing four representative types of ultrasmall fluorescent nanoparticles (quantum dots, metal nanoclusters, lanthanide-doped nanoparticles, and carbon dots) for the detection of various targets (e.g., pH, metal ions, microRNA) at the in vivo level. Their design mechanism, sensing performance and potential application are discussed in detail. Finally, current challenges and future prospects toward more intelligent and clinically translatable in vivo biosensors are also discussed.