(706a) A Simple Two-Phase Synthesis/Ligand Exchange Reaction for Creating Biocompatible Quantum Dots

In this talk we describe a method for producing a wide variety of functionalized quantum dot nanocrystals using a simple one-pot synthesis and ligand exchange procedure. As prepared, most highly crystalline quantum dots are organically soluble and not suitable for biological applications. Significant attention has focused on thiol-based ligands that replace entirely the native hydrophobic ligands with customized ligands, many of which contain water-soluble functional functional groups. For a number of reasons, many of the common mono- and dithiol ligands are challenging to synthesize and purify, are difficult to stably exchange with existing ligands, compromise quantum yield, and/or diminish the colloidal stability of the quantum dots. To address these issues, we have utilized a two-phase reaction and exchange procedure to create unique dithiocarbamate ligands at the liquid-liquid interface which subsequently displace the native capping ligands present on the nanocrystal surface. Lacking an undesirable byproduct, the reaction does not require explicit purification of the thiolated ligand which improves the yield. Additionally, the new ligand naturally exchanges with the native ligand which then drives the previously organically-soluble nanocrystals entirely into the aqueous phase. There are several key benefits to this method. First is the ability to perform the reaction and exchange steps in a single vessel which simplifies the process. Second, dithiocarbamates have been shown to better preserve the luminescence properties of the nanocrystals (e.g., maintain high quantum yields in aqueous solutions). Third, the chemistry is general and allows for a wide range of potential ligands opening the possibility for targeted delivery and unique interactions with their surroundings. A diversity of molecules such as amino acids, proteins, glycans, and polymers can be modified in a straightforward manner to serve as capping ligands on quantum dots.