Gold Nanostructures for Sensing and Functional Bioimaging

Gold nanostructures offer an extremely promising path forward in the fields of imaging and sensing because of their unique optical and chemical properties. Here, we demonstrate that plasmonic nanostructures can be employed as nanoscale transducers to monitor the growth and phase transitions in ultrathin polymer films. In particular, gold nanorods with high refractive index sensitivity (~150 nm / refractive index unit (RIU)) were employed to probe the growth and swelling of polyelectrolyte multilayers (PEM). By comparing the wavelength shift and extinction intensity of the localized surface plasmon resonance (LSPR) of the gold nanorods coated with PEM in air and water, the swelling of PEM was estimated to be 26%±6%, which was confirmed with AFM imaging in air and water. The deployment of shape-controlled metal nanostructures with high refractive index sensitivity represents a novel and facile approach for monitoring the phase transition in polymers with nanoscale resolution. Additionally, we demonstrate bio-enabled synthesis of a novel class of functional SERS probes with built-in and accessible electromagnetic hotspots, which are formed by densely packed satellites grown on a gold plasmonic core. These accessible electromagnetic hotspots enable facile sampling of the surrounding complex biological milieu. The core-satellite superstructures serve as nanoscale sensors to spatiotemporally map intravesicular pH changes along endocytic pathways inside a living cell. Furthermore, we show that through rational choice of core shape, photothermal efficiency of the nanostructures can be modulated to realize either of the following: imaging probes with minimal heating, or multifunctional theranostic agents that can image and photothermally kill the cells for locoregional therapy. Bright, stable and multifunctional exogenous contrast agents are critical for advancing surface enhanced Raman scattering (SERS)-based functional bioimaging and image-guided therapy