Industrial-scale chemical synthesis of gold nanorods: process optimization and 30 L scale-up toward GMP manufacturing

Gold nanorods (GNRs) offer unique photonic properties but remain challenging to reproduce and scale beyond bench volumes. We identify the critical process parameters (CPPs) governing the seed-mediated synthesis of CTAB-stabilized GNRs and translate the process from 30 mL to 30 L. Silver nitrate loading, seed formation (temperature and NaBH4-addition mixing), and growth-phase hydrodynamics emerge as key drivers of the longitudinal LSPR (LLSPR). Tight control of seed temperature and vigorous mixing during reductant addition yield batch-to-batch LLSPR variations within ± 20 nm; introducing gentle agitation during growth suppresses uncontrolled thermal convection, further improving robustness. The optimized protocol produces optically consistent GNRs at 3 L and 30 L with plasmonic features comparable to lab scale. Beyond the experimental advance, this work frames an industrially relevant route to large-scale chemical production of GNRs, establishing process understanding, reproducibility, and quality criteria that underpin future GMP manufacturing design and ongoing regulatory interactions.