The observation of chirality on inorganic nanoparticles (NPs) systems is an interesting and highly important phenomenon which has recently attracted considerable attention and has become a hot topic in nanoscience research. Many novel and interesting properties of chiral NPs have been explored and studied, showing that these systems could be of significant importance in both fundamental and application-oriented research. In particular, chirality of NPs is envisaged as an important parameter in the so called miniaturization race, with the aim of obtaining nanosized systems with controlled surface plasmon mediated circular dichroism (SP-CD) responses in the visible-near IR upon irradiation with circular polarized light. Progress in this area has been so far impeded by longstanding practical challenges represented by the structural complexity of the nanosized chiral systems reported so far, which necessitated complicate synthetic procedures. Thus, the development of an efficient and robust way of assembling nanocomponents represents one of the leading challenges that nanoscience is facing nowadays.
Very recently we have introduced a new strategy for designing and preparing chiral NPs which relies on a gelator fiber-templated approach in which the local organization is driven by the information already inscribed on the gel fibers. Plasmonic circular dichroism was obtained by chiral 3D organisation of gold nanorods (GNRs), generated by their self-assembly onto a gel fiber template with twisted morphology. Circular dichroism measurements revealed intense plasmon-induced Cotton effect, and the highest anisotropy factor for metal nanoparticles in solution reported so far. The original concept behind this system is as simple as effective: the use of pre-assembled fibrous materials with chiral morphology, formed, in this case, by an anthraquinone based oxalamide gelator. The fibers are used as chiral template for 3D arrangement of GNRs and for chirality transfer from supramolecular fibers, i.e., the twist and pitch of the obtained nanotapes of the gelator are responsible for the chiral organization of NRs and the observed SP-CD.
The aim of this project is to gain a molecular-level understanding of the interaction of NPs with the gelators within the gel matrix and of the origin of the chirality observed in the inorganic NPs. Furthermore, a comprehensive understanding of the mechanism of the twist formation and control the chiral twists in anthraquinone based oxalamide gelator assemblies will be sought. The long-term objective of this project is to explore the correlation between the morphology of the chiral gel fibers and the SP-CD responses of NPs. More specifically, the project will focus on (1) the preparation of nanocomposite chiral materials built-up from supramolecular fibers of different morphology serving as templates for surface assembly of NPs directed through the cooperation of selected molecular functionalities; (2) the screening of their optical properties and on identifying the factors responsible for an efficient optical enhancement; (3) the determination of the characteristics and the origins of the chirality in NPs.
The research field which studies nanoscale chirality has advanced significantly, especially considering introduction of molecular chirality into nano-building blocks and translation of the concept into functional systems with application potential. Without doubt, the synthesis of optically active NPs and understanding of their interaction would open the way to many applications particularly in negative index materials. On the other hand, inorganic NPs have shown great potential in medical diagnostics and cancer therapy. Thus, an efficient transfer of chirality from the molecular to the nanometer scale and extension of bio-applications of such systems is of high importance.
We strongly believe that this project will enable a rational design of a large number of nanoparticle superstructures and, more importantly, allow control of their structural characteristics, properties and ultimately enable their various applications. Such nanoparticle–organogel mixtures provide indeed interesting systems for assembling of NPs and studying the influence of chiral gel fibers on the optical activity of the resulting nanocomposites. Therefore, the proposed research will surely have a profound impact on the current knowledge on the optically active inorganic nanoparticles, their properties and possible applications.