2, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
For a number of decades, the study and development of colloidal semiconductor nanocrystals has become a rich field toward quantum dot (QD) integration into applications ranging from photovoltaics and photocatalysis to inks for printed electronics to biomedical imaging and drug delivery. Cadmium-based colloidal QDs are some of the most extensively studied semiconductor nanocrystals, and thus represent a model system for much needed surface chemistry investigations/descriptions toward any potential application. Essentially, the challenges in providing a full thermodynamic profile for nanocrystal surface chemistry must be overcome if QD-based technologies are to reach their full potential. This work will highlight how even in such a well-studied QD system, there are several caveats for appropriately compiling a thermodynamic profile in situ for the dynamic nature of their surfaces. It is imperative to consider the impact on the QD surface in the various surrounding media from the purification stage and on through surface modification reactions. Our lab has focused on further developing metrics for investigating colloidal nanoparticle surfaces while perturbing the environment as little as possible. We have established a highly effective and novel gel permeation chromatography approach to nanoparticle purification, which is ideal for investigating QD surface interactions with common spectroscopic tools; as well as investigating QD-ligand thermodynamics with isothermal titration calorimetry (ITC). In fact, where spectroscopic techniques have been limited in providing a full description of QD-ligand interactions, we have demonstrated the capability of ITC to detect binding phenomena responsible for drastic effects on QD photo-physical properties.