Seeing subtle nanoparticle differences A challenge in the fabrication of nanoparticles is that even for particles of uniform size, there will still be a distribution in the atomic arrangements and surface capping ligands from one particle to the next. Using liquid-cell transmission electron microscopy, Kim et al. reconstructed the structure of individual nanocrystals synthesized in one batch while they were still in solution. A comparison of multiple particles showed structural heterogeneity and differences between the interior and the outer shell of the individual nanoparticles, as well as nanoparticles containing extended defects and thus differences in internal strain, all of which can affect the physical and chemical properties of each particle. Science , this issue p. 60