Oleic acid rearrangement enables facile transfer of red-emitting quantum dots from hexane into water with enhanced fluorescence

There is significant demand for the conversion of hydrophobic nanoparticles (NPs) into water-soluble NPs, particularly for the transfer of photoluminescent quantum dots (QDs) synthesized in organic solvents into water-based settings. However, these transfer processes are often inefficient, with only a fraction of the QDs transferred into water, and typically result in decreases in photoluminescence quantum yield (PLQY). Here, we demonstrate a straightforward technique to efficiently transfer oleic acid (OA)-coated CdSe/CdS core-shell QDs into water without the addition of any new reagents. In contrast to the decrease in PLQY that is usually observed when QDs are transferred into water, this process in fact leads to an increase of the PLQY after transfer in basic water (pH 8). The process is highly reproducible and can be applied to other oleic acid-coated NPs. Density-functional-theory (DFT) calculations indicate that the QD transfer into water is enabled by the rearrangement of OA ligands at the surface of the QDs. This discovery allows for widely available, hydrophobic OA-coated QDs to be used in water media without any further modification and with enhanced fluorescence.