One Approach for Two: Toward the Creation of Near-Infrared Imaging Agents and Rapid Screening of Lanthanide(III) Ion Sensitizers Using Polystyrene Nanobeads

The unique luminescence properties of lanthanide(III) ions (Ln3+) in the near-infrared (NIR) range are attracting major attention in view of their exciting applications in the fields of technology, telecommunications, biology, and medicine. One of the main strategies to design luminescent Ln3+-based compounds relies on their sensitization through appropriate chromophoric ligands. The choice of the chromophores depends on the nature of Ln3+ and, as of today, still partially requires experimental trials, in particular, for the creation of luminescent compounds incorporating NIR-emitting Ln3+. The synthesis of organic ligands bearing suitable coordinating and chromophoric units is time- and effort-consuming. We have established a strategy to encapsulate a large number of Yb3+ trifluoromethanesulfonates and 1,n-dihydroxyanthraquinone chromophores in NH2-functionalized 100 nm polystyrene (PS) beads through a rapid swelling process, leading to AQ1,nOH-Yb@PS/NH2 (n = 4, 8). We have shown that 1,n-dihydroxyanthraquinones can act as antennae and sensitize the characteristic Yb3+ emission in the NIR upon excitation at 465 nm. To validate the bioapplicability of these luminescent beads, polyethylene glycol (PEG)-coated beads have been prepared (AQ1,nOH-Yb@PS/PEG) and demonstrated to be noncytotoxic for HeLa cells up to 500 μg/mL. Confocal microscopy experiments have shown that AQ1,nOH-Yb@PS/PEG is taken up by HeLa cells, whereas epifluorescence microscopy confirmed the possibility of detecting the NIR Yb3+ emission in living cells. The developed strategy has a high potential and can be further applied for the rapid screening of sensitizers for different NIR-emitting Ln3+ ions and for the creation of smart NIR-emitting imaging agents.