Correlating In Situ Growth Kinetics with Nanorod Morphology Using iSCAT-FlucCS

Anisotropic growth in seed-mediated nanocrystal synthesis depends on nucleation and autocatalytic growth, and the aspect ratio is expected to be related to the ratio of growth to nucleation rates. Direct kinetic evidence for this link is limited, because it is difficult to measure both kinetics and morphology in the same experiment. In this work, we examined the growth kinetics of seed-mediated silver nanorods and linked them to their shapes using a dual-mode platform, iSCAT-FlucCS. We measured nucleation (k1) and growth (k2) kinetic parameters in situ with wide-field iSCAT microscopy and compared them to nanorod dimensions obtained from iSCAT fluctuation correlation spectroscopy. We found that k2 increased with seed concentration, and k1 shows no clear monotonic dependence on seed volume, modestly high at low seed levels. The nanorod aspect ratio decreased as k2/k1 rose above a certain point, suggesting a shift from seed-limited to monomer-limited growth, with more variability below this threshold. These findings provide direct kinetic evidence that competition between nucleation and growth shapes seed-dependent nanorod anisotropy.