Orientation of hard semiconducting nanoparticles by soft lyotropic lipid constructs*

Quantum nanorods (QnR) are fluorescent nanoparticles with tunable optoelectronic properties depending on size and shape. These properties make them attractive in many biotechnology applications but due to their hydrophobic nature they are often hybridized by a shell of soft amphiphilic molecules. Anisotropic nanocrystals have orientation dependent properties, however controlling QnR alignment when drying from an organic solvent is difficult. We investigate the ability of amphiphilic molecules that are mostly known as stabilizers of QnRs in water to act as a matrix to guide QnR orientational order. Lipids are amphiphilic molecules that rapidly assemble into hierarchic liquid crystalline structures with various levels of positional and orientational order. These structures rapidly experience phase transitions depending on lipid composition, relative humidity, and temperature. Here we use glancing-incidence small angle X-ray diffraction (GI-SAXS) and fluorescence microscopy to study the co-assembly of lipid – QnR composites in highly concentrated regimes. Conditions are found to promote either the separation into lipid and highly ordered QnR domains, or the mixture of these components into a single phase with distinct structural characteristics.