Functionalized nanoparticles (NPs) receive interest for application in light-energy conversion, imaging and sensing, and photomedecine. Often, the particles are dispersed as individual entities in a liquid, in the ideal case behaving as a colloidal solution. The interaction of NPs with light can then be studied with solution-phase spectroscopy,[1] much like molecular systems, and understood through theoretical models. This requires knowledge of the structure of the NP objects in solution, which may evolve through aggregation,[1] ligand exchange, oxidation etc. We found that the concerted measurement of the spectroscopic and hydrodynamic behaviour of NPs in solution aids in understanding NPs and NP assemblies developed for aforementioned applications. These measurements were achieved in a number of ways: spectroscopy coupled to microfluidics,[2] and 'confocal' microspectroscopy (e.g., fluctuation correlation spectroscopies).[3] The experimental results can be quantitatively understood via theoretical models taking into account the structures of the nano-objects. - [1] https://doi.org/10.1039/c6nr00918b - [2] https://doi.org/10.1002/ppsc.202000187 - [3] https://doi.org/10.1002/cphc.201701228 -