Plasmonic nanoparticles are used in a wide variety of applications over a broad array of fields including medicine, energy, and environmental chemistry. The continued successful development of this class of materials requires the accurate characterization of nanoparticle stability for a variety of solution-based conditions. Although a wide array of methods exist, there is an absence of a unified, quantitative means for complete nanoparticle characterization. This work focuses on the challenges inherent with current methods through a comparative analysis of the current gold standard characterization methods. I propose using capillary electrophoresis and micro-capillary electrophoresis as powerful tools for better quantifying the inherent polydispersity and differences in surface functionalization within a nanoparticle sample. I present the Particle Instability Parameter (PIP) as a robust, quantitative, and generalizable characterization technique based upon UV-Vis absorbance spectroscopy to characterize colloidal instability. I validate PIP performance with both traditional and alternative characterization methods by measuring gold nanorod instability in response to different salt (NaCl) concentrations and as a function of solution pH, salt, and buffer type. I contextualize these methods within the literature on gold nanoparticle characterization to establish a standardized methodology for nanoparticle analysis. Finally, I present a concept for an integrated biodiagnostics platform using gold nanorods based upon an integrated microfluidic microspectrophotometry system for the detection of pathogens.