In Situ Analysis of Chiral Gold Nanorod Growth by Nanofluidic Liquid-Phase Electron Microscopy

Chiral gold nanoparticles exhibit unique chiroptical properties, but their integration into plasmonic devices requires an understanding of the formation of chiral features and controlling their growth on substrates. Here, we combine microfluidic synthesis and liquid-phase transmission electron microscopy (LP-TEM) to study the growth of chiral wrinkled gold nanorods (AuNRs). Microfluidic growth from AuNR seeds produced g-factors of up to 0.01, approaching values reported for colloidal synthesis. Complementary LP-TEM experiments in a nanofluidic reactor generated gradients of gold precursor and reducing agent concentrations, enabling the direct observation of wrinkle formation under different conditions within a single experiment. Both methods showed that a higher gold precursor availability promotes longer wrinkles and stronger chiroptical activity. Higher flow rates in microfluidics produced larger nanoparticles with enhanced chiroptical responses, while LP-TEM revealed that increased reducing agent concentrations accelerate wrinkle growth. Reagent depletion ultimately limits the growth. Overall, wrinkle development is governed by precursor availability and reduction kinetics, determining the chiroptical performance.