Optically-resonant nanoparticles are used in medicine and metamaterials. Their resonant properties depend upon nanoparticle morphology, dimensions, organization relative to each other, and their environment. I will demonstrate this using three examples.

Gold nanoparticles can be used as photothermal conversion agents in the treatment of cancer. In the first example, gold nanorods were synthesized through a seedless approach using a binary surfactant mixture to control their morphology and optical properties during their production. The use of a co-surfactant enabled significant improvements in the monodispersity, shape yield, and scalability of the protocol. The synthesized gold nanorods were functionalized with phospholipids andthe effective removal of toxic CTAB demonstrated. The phospholipid-functionalized nanorods had improved colloidal stability compared to other surface functionalizations studied. The nanorods were also shown to be non-toxic in vitro and in vivo. The biodistribution of these particles was explored when passively targeted or actively targeted with cancer-specific adhirons. Thanks to their morphology, these nanorods were capable of generating sufficient quantities of heat, for photothermal therapy and photoacoustic imaging.

Photothermal therapy can be achieved with other gold morphologies, such as gold nanoplates produced through the use of biomineralization peptides. These peptides are capable of reducing gold salts, selectively capping specific facets, and stabilizing synthesized particles in a single step. Currently, we have fairly poor control over syntheses using these peptides. The optical properties of these particles were improved by studying the effects of temperature, pH, peptide concentration, and peptide sequence on the synthesis. Their potential was demonstrated for use in photothermal therapy through in vitro studies.

Finally, I will discuss the synthesis and self-assembly of plasmonic and Mie-resonant nanoparticles for metamaterials. In particular, of interest to my work, is the production of particles that satisfy the 'Kerker condition', which produces magnetic and electric resonances at the same wavelength of light, resulting in pure forward light scattering. When such materials are combined into 2D assemblies, they could enable the manipulation of light in new ways, such as the creation of perfect absorbers or wave-front shaping (flat lenses, vortex beams, beam deflectors, …). Unusual scattering patterns can be created by engineering the magnetic resonances occuring within individual nanoparticles. We have sought to find routes to fabricate both the nanoparticles and the materials through purely bottom-up self-assembly approaches. The resonant particles with which I have worked consist of symmetric plasmonic clusters, Mie-resonant Si@SiN_xO_y core-shells, and Si@Au core-shells. I have then created 2D materials through both convectively-driven dip-coating and interfacial self-assembly. We have studied how the optical properties shift between the individual particles and the assemblies on a substrate.