Real-Time Observation of Thermal Reshaping Mechanisms in Gold Nanostars

Gold nanostars (AuNS) exhibit morphology-dependent optical properties that make them attractive for photothermal and photoacoustic applications; however, their limited thermal stability remains a critical challenge. In this work, we investigate the thermal behavior of AuNS synthesized using Good’s buffers, specifically 4-(2-hydroxyethyl)-1-piperazinepropanesulfonic acid (EPPS) and 3-( N -morpholino)propanesulfonic acid (MOPS), by combining ex situ and in situ characterization techniques. Ex situ heating revealed collective deformation at elevated temperatures, while in situ heating enabled the real-time observation of individual particle reshaping. AuNS–EPPS displayed reshaping rates more than twice those of AuNS–MOPS, caused by both the thermal treatment and electron beam effects. Direct visualization revealed gold migration from branches to the core, a mechanism previously hypothesized. Despite pronounced morphological changes, the crystal structure remained intact. These results clarify the deformation mechanisms of AuNS and inform the design of more thermally robust nanostructures for (photo)thermal applications.