(Keynote) Quantum Dot Coatings for Aqueous Stabilization and Applications in Biomolecular Analysis

Abstract

Semiconductor quantum dots have been commercially available as molecular probes for applications in the life sciences and clinical diagnostics for two decades, however they have only been adopted in niche applications. Part of the reason for limited adoption is attributable to challenges in colloidal stabilization, as these solid nanocrystals tend to aggregate and nonspecifically adsorb to surfaces and cellular structures. This can largely be alleviated by use of nanocrystal coatings that resist nonspecific binding and promote aqueous dispersion, however the vast majority of such coatings are based on neutral and zwitterionic polymers that add considerable hydrodynamic size to the product. This size increase is due to the bulk of the coating itself as well as adsorption of water molecules and ions in solution. The size increase causes steric hindrance and inaccurate molecular labeling when these probes are used to analyze targets that have considerable size or ones that are located in crowded regions of cells or tissues. Furthermore, the bioaffinity label that attaches the quantum dot to its intended molecular target often contributes substantially to the final size and stability of the probe. This is especially challenging for protein labeling using antibodies, which themselves are fairly large proteins that attach heterogeneously to quantum dots, typically yielding large, polydisperse products. This talk will focus on developments in quantum dot engineering, monolayer polymeric coatings, and bioconjugation strategies to optimize offsetting characteristics of size, homogeneity, bioaffinity, and specificity. In particular, multidentate polymer coatings in recent years have enabled the production of quantum dots with long-term shelf life, small hydrodynamic diameters, and efficient click chemistry conjugations. By tuning the conjugation methods to antibody fragments and single-stranded DNA, we can now prepare bioaffinity labels for proteins and nucleic acids in the ~10 nm range, with further size reductions possible through nanocrystal heterostructure engineering. This talk will also cover how in situ protein and nucleic acid labeling applications can benefit from these advances in addition to current challenges in processing, scale-up, and user adoption.