Mirror symmetry breaking in materials is a fascinating phenomenon that has practical implications for various optoelectronic technologies. Chiral plasmonic materials are particularly appealing due to their strong and specific interactions with light. In this work we broaden the portfolio of available strategies toward the preparation of chiral plasmonic assemblies, by applying the principles of chirality synchronization—a phenomenon known for small molecules, which results in the formation of chiral domains from transiently chiral molecules. We report the controlled cocrystallization of 23 nm gold nanoparticles and liquid crystal molecules yielding domains made of highly ordered, helical nanofibers, preferentially twisted to the right or to the left within each domain. We confirmed that such micrometer sized domains exhibit strong, far-field circular dichroism (CD) signals, even though the bulk material is racemic. We further highlight the potential of the proposed approach to realize chiral plasmonic thin films by using a mechanical chirality discrimination method. Toward this end, we developed a rapid CD imaging technique based on the use of polarized light optical microscopy (POM), which enabled probing the CD signal with micrometer-scale resolution, despite of linear dichroism and birefringence in the sample. The developed methodology allows us to extend intrinsically local effects of chiral synchronization to the macroscopic scale, thereby broadening the available tools for chirality manipulation in chiral plasmonic systems.

The development of plasmonic nanomaterials with chiral geometry has drawn extensive attention owing to their practical implications in chiral catalysis, chiral metamaterials, or enantioselective biosensing and medicine. However, due to the lack of effective synthesis methods of hydrophobic nanoparticles (NPs) showing intrinsic, plasmonic chirality, their applications are currently limited to aqueous systems. In this work, we resolve the problem of achieving hydrophobic Au NPs with intrinsic chirality by efficient phase transfer of water-soluble NPs using low molecular weight, liquid crystal-like ligands. We confirmed that, after the phase transfer, Au NPs preserve strong, far-field circular dichroism (CD) signals, attesting their chiral geometry. The universality of the method is exemplified by using different types of NPs and ligands. We further highlight the potential of the proposed approach to realize chiral plasmonic, inorganic/organic nanocomposites with block copolymers, liquid crystals, and compounds forming physical gels. All soft matter composites sustain plasmonic CD signals with electron microscopies confirming well-dispersed nanoinclusions. The developed methodology allows us to expand the portfolio of plasmonic NPs with intrinsic structural chirality, thereby broadening the scope of their applications toward softmatter based systems.

Self-assembly of metal nanoparticles has applications in the fabrication of optically active materials. Here, we introduce a facile strategy for the fabrication of films of binary nanoparticle assemblies. Dynamic control over the configuration of gold nanorods and nanospheres is achieved via the melting of bound and unbound fractions of liquid-crystal-like nanoparticle ligands. This approach provides a route for the preparation of hierarchical nanoparticle superstructures with applications in reversibly switchable, visible-range plasmonic technologies.

Gold nanoparticles (Au-NPs) are among the most commonly used materials for increasing the sensitivity of Raman spectroscopy. This is mainly due to the strong and tunable surface plasmon resonances, which can be easily adjusted by choosing the shape and size of individual NPs. However, recent findings indicate that controlling the density of NPs in their assemblies is an equally important parameter. An efficient way to achieve such control is by using the Langmuir–Schaefer technique, which yields single-layer assemblies of NPs on a solid substrate. In this study, we correlate the density and thermodynamic properties of a monolayer of spherical Au-NPs with their performance as Raman substrates. Hence, hydrophobic NPs were synthesized and assembled into films using the Langmuir–Schaefer technique. The surface-enhanced Raman spectroscopy (SERS) showed various degrees of enhancement depending on the different ranges of transfer surface pressures employed, which almost doubled the expected SERS signal intensity at the highest deposition surface pressure. To gain greater insights into this phenomenon, we investigated the NP distribution in the Langmuir and Langmuir–Schaefer films by detailed spectroscopic and electron and optical microscopic analyses. A correlation was observed between NP enhancements on the micro- and nanoscale. The presented results demonstrated the potential of adjusting the Raman responses in ultrasensitive detection by controlling the thermodynamic properties of NP monolayers.