Decoupling Absorption and Scattering Reveals Nanoscale Structural Evolution of Plasmonic Nanostructures in Real Time.

Plasmonic nanostructures are of broad interest because of their ability to confine light into deeply subwavelength volumes. Precise structural control is essential for tuning plasmonic response, yet achieving such control requires an understanding of growth dynamics. This remains challenging in delicate colloidal environments and requires noninvasive tools. Although UV-Vis spectroscopy is widely used to follow nanoparticle growth, it provides only an apparent optical loss signal, in which absorption and scattering are merged and key information on radiative plasmon evolution is obscured. Here, an automated optical platform is reported for real-time tracking of absorption and scattering from plasmonic nanostructures in solution. The method is validated by simulations and shown to be applicable to nanoparticles with different shapes and modal characteristics. It reveals optical information inaccessible to conventional extinction spectroscopy, including coupled plasmon modes during Au nanoparticle aggregation and three distinct growth stages during Au nanorod formation. Notably, the transition from longitudinal-dominated to transverse-dominated growth coincides with inversion of the scattering-to-absorption ratio, providing an optical signature that links growth anisotropy to the redistribution of radiative and nonradiative plasmon responses. These results demonstrate that absorption and scattering serve as practical, complementary probes for tracking nanoscale growth pathways in plasmonic nanostructures.