Surface-engineered cationic nanocrystals stable in high ionic strength solutions

Dmitry Dirin^a, Ryan Dragoman^a, Marcel Grogg^b, Maryna Bodnarchuk^a^,^c, Peter Tiefenboeck^d, Donald Hilvert^b, Maksym Kovalenko^a^,^c

^aETH Zurich, Laboratory of Inorganic Chemistry, Department of Chemistry & Applied Biosciences, Vladimir-Prelog-Weg, 1, Zürich, Switzerland

^bETH Zürich, Department of Chemistry and Applied Biosciences, Switzerland, Switzerland

^cEMPA - Swiss Federal Laboratories for Materials Science and Technology, Überland Strasse, 129, Dübendorf, Switzerland

^dETH Zürich, Department of Chemistry and Applied Biosciences, Switzerland, Switzerland

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe September Meeting 2017 (NFM17)

SE1: Fundamental Processes in Semiconductor Nanocrystals

Barcelona, Spain, 2017 September 4th - 9th

Organizers: Arjan Houtepen and Zeger Hens

Poster, Dmitry Dirin, 172
Publication date: 20th June 2016

Progress in colloidal synthesis in the last two decades has enabled high-quality semiconductor, plasmonic, and magnetic nanocrystals (NCs). As synthesized, these NCs are usually capped with long-chain apolar ligands. Post-synthetic surface functionalization is required for rendering such NCs colloidally stable in polar media such as water. However, unlike small anionic molecules and polymeric coatings, producing positively charged stable NCs, especially at high ionic strengths, has remained challenging. Here we present a general approach to achieve aqueously stable cationic NCs using a set of small (<2.5 nm long) positively charged ligands. The applicability of this method is demonstrated for a variety of materials including semiconductor CdSe/CdS core/shell NCs, magnetic Fe@Fe₃O₄, Fe₃O₄, and FePt NCs, and three different classes of plasmonic Au NCs including large nanorods. The obtained cationic NCs typically have zeta potential values ranging from +30 to +60 mV and retain colloidal stability for days to months in several biological buffers at elevated pH and in concentrated salt solutions. This allowed us to demonstrate site-specific staining of cellular structures using fluorescent cationic NCs with several different surface chemistries. Furthermore, colloidal stability of the obtained NCs in the presence of other charged species allowed the assembly of cationic and anionic counterparts driven primarily by electrostatic attraction. With this approach, we prepare highly uniform 3D and 2D binary mixtures of NCs through induced homogeneous aggregation and alternating-charge layer-by-layer deposition, respectively. Such binary mixtures may provide a new route in the engineering of nanocrystalline solids for electronics, thermoelectrics, and photovoltaics.

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