Development and validation of a static multiple light scattering (SMLS) method for real-time colloidal stability assessment in nanoparticle formulations

This study presents the first development and validation of a static multiple light scattering (SMLS)-based method for real-time, non-invasive assessment of nanoparticle colloidal stability. Nanoparticles, leveraging their nanoscale advantages (e.g., targeted delivery, enhanced drug solubility, and controlled release), hold transformative potential in treating diseases. However, their clinical success hinges on colloidal stability, which dictates in vivo behavior, safety, and regulatory compliance. While dynamic light scattering (DLS) remains widely used, its inability to monitor dynamic transformations and reliance on sample dilution limit its accuracy. Here, we pioneer the application of SMLS to systematically evaluate colloidal stability across standardized particles and commercial nanoparticle formulations (liposomes, nanoparticles, micelles, and nanoemulsions). Results demonstrate that SMLS captures destabilization kinetics (aggregation, sedimentation, creaming) in real-time without dilution, even at high concentrations, while DLS fails to distinguish polydisperse systems due to time-point sampling. The Turbiscan stability index (TSI) quantifies instability mechanisms, correlating with particle size distribution broadening. This first comprehensive validation of SMLS for nanoparticles reveals its superiority in reflecting native-state behavior, exemplified by minimal or the variations in the average transmission (ΔT) or backscattering intensity (ΔBS) fluctuations and low TSI values in four commercial formulations. By addressing a critical technological gap, this study establishes SMLS as an indispensable tool for optimizing nanoparticle design, ensuring compliance with U.S. Food and Drug Administration (FDA) in-use stability guidelines, and accelerating clinical translation.