These are standard tests used in the pharmaceutical industry to investigate the potential instability of drug substances (the active pharmaceutical ingredient-API) or drug products (the API formulated with the appropriate excipients). They are performed to give information regarding potential shelf-life/ formation of toxic compounds etc. in a relatively short-time frame.
The stressed samples are analyzed (virtually always by HPLC/UV) to determine how many degradation products are formed, and at what levels.
You might typically prepare samples at 1 mg/mL for HPLC analysis. Search the literature to discover any known degradation products of your nanoparticles; failing that, draw the chemical structures and then try to predict the action of acid/base/oxidative stress etc.
Another important stress test is with UV and full-spectrum light.