Surface-enhanced Raman scattering (SERS) is a highly sensitive technique that detects trace amounts of biological, chemical, and radiologically-relevant molecules based on enhanced vibrational signals using plasmonic nanoparticles. Reproducible SERS signals, however, require stable optical properties of nanoparticles. My thesis focuses on addressing this challenge by promoting reproducible SERS detection of small molecules through materials design and both fundamental and applied studies. Importantly, the influence of intermolecular interactions on vibrational spectroscopy is revealed.