Plasmon Resonance Dynamics of Surface-Modified Gold Nanoparticles Explored Through Optical and X-ray Spectroscopy

Gold nanoparticles (GNPs) have attracted great attention over the last few years because of their versatility to confine light at the nanometer scale, creating geometry-controlled hotspots of intense electromagnetic fields. While spherical (isotropic) GNPs are the most widely employed, our research focuses primarily on nanorods (anisotropic), as their localized surface plasmon resonance (LSPR) can be tuned across the entire UV/Vis/NIR spectral range. Our highly precise, pH-driven synthesis approach achieves this tunability, which enables targeted surface modification and electrostatic attachment of adsorbates or dye molecules. We employ ground-state absorption spectroscopy and scanning/transmission electron microscopy to elucidate the surfactant- and size-associated LSPR shifts, surface-enhanced Raman and Fourier-transform infrared spectroscopy to analyze the photo-excited populations of GNP-adsorbate complexes, and two-dimensional X-ray absorption near-edge spectroscopy to study LSPR-induced shifts in the core-electronic transitions of different GNP lattice facets. With this extensive study of nanoscale plasmon-molecule interactions, we offer pivotal insights for applications in solar energy, photodynamic cancer therapy, surface catalysis, and the semiconductor industry.