In the last few decades, researchers have massively in- In the future, quantum dots or nanocrystals may also play creased the quantum e昀케ciency of quantum dots. This a key role in medical applications — for example, in order was initially around 5% — in other words, it took 20 to visualize certain tissues. This is another focal point of photons of excitement to produce one photon of emitted our research. light. In modern quantum dots, the e昀케ciency stands at almost 100%. In part, this improvement was achieved by SNI INSight: Does your team also work with encasing the nanocrystals in an inorganic shell — like an quantum dots? onion having di昀昀erent layers. Jonathan de Roo: We don’t work with quantum dots, It is also important to adjust the reaction conditions so but we do use non-toxic colloidal nanocrystals made of that particles reach the target size at the end of the reac- zirconium and hafnium oxide. These are close relatives tion. To obtain small quantum dots, I can obviously take of quantum dots and are produced in a similar manner. my samples right at the start of the reaction and halt crystal growth — but then I lose most of the reagents. SNI INSight: What applications are you exploring The aim is to choose components and conditions with a for these nanocrystals? view to maximizing yield by making optimum use of the starting materials. This is another area where researchers Jonathan de Roo: We want to use the nanocrystals for have made considerable progress. diagnostic imaging. SNI INSight: What are quantum dots used for? In a project with colleagues from Ghent University Hos- pital (Belgium), we’re investigating whether the crystals Jonathan de Roo: Today, quantum dots are used in nu- can be used to boost soft-tissue contrast in X-ray exam- merous areas. For example, they are responsible for the inations. By doing so, we hope to pave the way for the brilliant colors in QLED televisions, where blue light is clear identi昀椀cation of “sentinel lymph nodes” in breast emitted by a gallium nitride light source and then con- cancer patients during surgery. To this end, the nanocrys- verted into green and red by the various quantum dots. tals are injected into the tumor, the liquid containing the These three primary colors can then be combined to pro- nanocrystals 昀氀ows through the lymph system to the 昀椀rst duce the full color palette. lymph node in the armpit, and this sentinel lymph node becomes visible in the X-ray image. As the solution carries In QLED lamps, quantum dots convert colors more e昀케- a dye, the surgeons can then visualize the sentinel lymph ciently than is the case with traditional LEDs, although nodes for removal during surgery. these QLED lamps are not yet commercially available. It is 昀椀rst necessary to improve the stability of the quantum In an SNI project, we’re working with colleagues from dots because, unlike a TV screen, an LED lamp becomes the PSI in order to use our nanocrystals to spot rejection very hot and can therefore cause the quantum dots to at an early stage in transplant patients. First, we equip “die o昀昀.” the nanocrystals with certain antibodies that bind spe- ci昀椀cally to immune cells. Then, if we add our antibody The nanocrystals from the de Roo team can be used to produce detailed images of even the 昀椀nest blood vessels in the gills of a zebra昀椀sh. (Image: Department of Chemistry, University of Basel) SNI INSight December 2023 6