Applications of quantum dots with upconverting luminescence in bioimaging

Quantum dots (QDs) have attracted great attention in recent years due to their promising applications in bioimaging. Compared with traditional ultraviolet excitation of QDs, near-infrared laser (NIR) excitation has many advantages, such as being less harmful, little blinking effects, zero autofluorescence and deep penetration in tissue. Composing QDs with upconverting properties is promising to enable NIR excitation. This article provides a review of QDs with upconverting luminescence and their applications in bioimaging. Based on the mechanisms of luminescence, discussion will be divided into four groups: nanoheterostructures/mixtures of QDs and upconverting nanoparticles, graphene quantum dots, lanthanide-doped QDs, and double QDs. The content includes synthetic routes, upconverting luminescence properties, and their applications in bioimaging.