Combined Interferometric Scattering Microscopy and Fluctuation Correlation Spectroscopy (iSCAT-FlucCS) for Measuring Nanostructures Growth and Size-Distribution

Controlling the morphology and structural homogeneity of nanostructures is vital to optimizing their potential applications. This necessitates a fundamental understanding of the involved kinetic rates and their optimization. In-situ analysis of nanostructure growth, which provides information on the associated morphology within the same sample, is essential for establishing accurate correlations. To observe in-situ growth, optimize kinetics, and map associated morphology, this study introduces the development of an experimental platform based on interferometric scattering (iSCAT). This platform enables simultaneous monitoring of growth kinetics via microscopy and the extraction of size distributions from the same sample, within the same reaction vessel, under identical conditions, through iSCAT fluctuation correlation spectroscopy (iSCAT-FlucCS), a bimodal system. Utilizing this platform, we investigate light-induced, seed-mediated synthesis of silver nanorods and systematically analyze the effects of precursor concentrations, seed volume, and illumination wavelength on both reaction rates and the final morphology of the synthesized nanostructures. The results demonstrate a direct correlation between kinetic rate constants and particle morphology; specifically, high nucleation rates favour the formation of spherical particles, whereas elevated autocatalytic growth rates, combined with suppressed nucleation, promote anisotropic elongation into nanorods. Additionally, we show that iSCAT-FlucCS can reliably and accurately recover particle size and size distribution, aligning with conventional ensemble averaging techniques. This work establishes iSCAT-FlucCS as a comprehensive, label-free, and non-invasive tool for probing, understanding, and ultimately controlling nanostructure synthesis dynamics and morphology, with potential applications in nanomaterials design, mechanistic investigations, and real-time reaction optimization.