The interaction between light and metal nanoparticles has been an expanding area of research due to their unique ability to focus light at the nanoscale due to their collective electron (plasmon) resonances. This property has resulted in many applications including photocatalysis, light-based cancer therapies, chemical sensing, and surface-enhanced spectroscopies. Recent interest has shifted from traditional plasmonic materials, Au and Ag, to Al due to its low cost, high abundance, and favorable properties in the ultraviolet spectral region. This thesis will discuss the synthesis, surface modification, and application of plasmonic Al nanocrystals and can broadly be broken in two sections. First, we develop a method for encapsulating Al nanocrystals in a thin coating of the bio-inspired polymer, polydopamine, for dramatic increases in aqueous stability. We examine the oxidation process of both bare and functionalized particles and characterize a high surface area oxide material obtained after oxidation. We then explore the multifunctional nature of polydopamine for its use as a capture layer for organic water pollutants, enabling their detection using surface-enhanced Raman scattering. Using this platform, we developed a low-cost assay capable of sub part-per-billion pollutant detection. Second, we develop a method for the chemical synthesis of sub-50 nm Al nanocrystals through manipulation of the solvent coordination environment during nanocrystal growth. These ultrasmall particles display a sharp resonance in the ultraviolet. We investigate the optical properties of the sub-50 nm particles and observe that they transition from a colorless/yellow solution to one that is opaque and black with increasing nanoparticle concentration. We study this phenomenon experimentally and theoretically and find that the near-infrared interband transition intrinsic to Al is the dominant mechanism for this increased broadband absorption. We then develop a simple method for silica functionalization of the Al nanocrystal surface, yielding the most oxidation-resistant Al nanocrystals thus far. Finally, we utilize these silica-encapsulated nanocrystals for photothermal heating, demonstrating their broadband absorption characteristics.