Probing chemistry, especially at the nanoscale, provides insight into the mechanisms governing chemical reactions at interfaces and potential avenues for materials development. As a class of materials, plasmonic nanomaterials are a promising approach for probing chemistry at interfaces. When excited with an incident electric field like light, plasmonic nanomaterials exhibit localized surface plasmon resonances (LSPR). The LSPR scattering spectrum is sensitive to the size, shape and local environment of the nanoparticle. However, this sensitivity can be a limiting factor in applications of plasmonic materials in complex chemical environments. Contaminants in the environment can corrode or dissolve the nanomaterials, irreversibly changing the LSPR. The intrinsic heterogeneity of colloidally synthesized nanoparticles limits LSPR sensitivity to changes in the dielectric environment at the ensemble level. In my work, I use single-particle spectroelectrochemistry and correlated scanning electron microscopy to investigate the overall stability and utility of plasmonic nanomaterials in complex chemical environments. I demonstrate that we can utilize the plasmon to report on chemistry in complex environments and provide mechanistic insight into dissolution, polymer collapse, and future work in switchable electron density tuning in single plasmonic nanoparticles. Understanding the mechanisms governing these chemical processes at the nanoscale builds foundational science to support future technological developments in electronics, catalysis, and sensing.