UC Riverside

Plasmonic nanostructures with tunable localized surface plasmon resonance (LSPR) have attracted much attention due to their broad applications in chemical sensing, photothermal therapy, and colorimetric detection. Because LSPR is related to particle morphology, controlling their size and shape is crucial for tailoring and tuning their optical resonance properties. Compared with conventional synthesis methods, space-confined seed-mediated growth is more reproducible and scalable and offers more opportunities to design hybrid and thermodynamically unstable structures. This dissertation discusses the seed-mediated growth of various plasmonic nanostructures within polymer confinement and explores their applications for colorimetric devices.We first investigate the confined seeded growth process of plasmonic nanostructures, which involves the deposition of various metal atoms, including Au, Ag, and Pt, onto the pre-formed seeds confined within polymer nanoshells. The key parameters affecting the growth are systematically studied, including the surfactants, reductants, and some kinetics factors. Different metals are found to exhibit diverse behaviors during the seeded growth process, producing plasmonic-polymeric hybrid nanostructures with different chemical and physical properties. In particular, we highlight the seeded growth of Pt within the confined space, which has not been achieved previously. These plasmonic nanostructures are promising building blocks for designing various colorimetric devices. The seeded growth process is coupled with a plasmonic decoupling mechanism to design a colorimetric pressure sensor that can respond to applied pressure with instant color changes. The sensor consists of a thin film of stacked uniform nanoshells of resorcinol formaldehyde resin, with their inner surfaces functionalized with Ag nanoparticles. Upon compression, the flexible polymer nanoshells expand laterally, inducing plasmonic decoupling between neighboring Ag nanoparticles and a subsequent blueshift. The initial color of the sensor is determined by the extent of plasmonic coupling, which can be controlled by tuning the interparticle distance through a seeded growth process. The sensing range can be conveniently customized by controlling the polymer shell thickness or incorporating the hybrid nanoshells into various polymer matrices. We further demonstrate that the controlled growth of plasmonic nanoparticles within polymer nanoshells offers an excellent opportunity for tuning their refractive index. Such tunability is employed to design novel colloidal photonic crystal films. Theoretical simulations coupled with experimental observations confirm the strong interaction between Au and resorcinol formaldehyde, which results in a notable decrease in the refractive index and a subsequent blueshift in the photonic bandgap. The photonic crystal films fabricated using such nanoshells exhibit brilliant structural colors, which can be conveniently controlled by the amount of Au loading through the seeded growth process. The tuning range of diffraction colors can be tailored by adjusting the diameter and thickness of the polymer nanoshells. This high spectral tunability enables the design of unique colorimetric refractive index sensors capable of distinguishing various polar solvents. Plasmonic nanoparticles can efficiently convert light of their resonance wavelength into heat. This photothermal effect is utilized to induce photoresponsive expansion of hollow polymer nanoshells, resulting in a color response in two-dimensional (2D) arrays assembled on a substrate using these nanoshells. When exposed to light, the liquid inside the polymer shells vaporizes quickly, creating high pressure that causes the shells to expand. The expansion can be controlled by adjusting light intensity, shell thickness, and void size. This expansion allows the nanoshells to reposition themselves, improving the order of the 2D arrays and, consequently, the optical diffraction. Additionally, the expansion causes a redshift in the structural color, enabling the development of a light-responsive writing technique.