Surface-Engineered Cationic Nanocrystals Stable in Biological Buffers and High Ionic Strength Solutions.

Area of Science:

• Materials Science
• Nanotechnology
• Colloid Chemistry

Background:

• Recent advances in colloidal synthesis yield high-quality semiconductor, plasmonic, and magnetic nanocrystals (NCs).
• Synthesized NCs typically feature long-chain apolar ligands, requiring postsynthetic functionalization for stability in polar media like water.
• Achieving stable, positively charged NCs, especially in high ionic strength solutions, remains a significant challenge.

Purpose of the Study:

• To present a general strategy for creating aqueously stable cationic NCs.
• To overcome limitations in producing positively charged nanomaterials for biological and materials science applications.

Main Methods:

• Utilized small (<2.5 nm) positively charged ligands for surface functionalization of NCs.
• Demonstrated the method across diverse NC types: semiconductor (CdSe/CdS), magnetic (Fe@Fe3O4, Fe3O4, FePt), and plasmonic (Au nanorods).
• Characterized NCs using zeta potential measurements and assessed colloidal stability in various buffers and salt solutions.

Main Results:

• Successfully produced stable cationic NCs with zeta potentials ranging from +30 to +60 mV.
• Achieved colloidal stability for days to months in biological buffers and concentrated salt solutions.
• Enabled site-specific cellular staining with fluorescent cationic NCs and facilitated assembly of binary NC mixtures.

Conclusions:

• The developed method provides a versatile approach for generating stable cationic NCs in aqueous environments.
• The resulting cationic NCs are suitable for biological applications and the fabrication of advanced nanocrystalline materials.
• This work opens new avenues for engineering 3D and 2D binary NC mixtures for applications in electronics, thermoelectrics, and photovoltaics.