Programming Nanoscale Reaction Environments via Peptide Localization for Gold Nanoparticle Growth in Liposomal Nanoreactors

Gold nanoparticles (AuNPs) exhibit size‐ and shape‐dependent physicochemical properties, yet precise morphological control under environmentally benign conditions remains challenging due to the lack of spatial regulation of nucleation and growth. Here, we explore liposome‐based nanoreactors as confined reaction fields for peptide‐mediated synthesis of AuNP. Unexpectedly, biomineralization peptides that form anisotropic and faceted nanostructures in bulk solution produce distinct morphologies within liposomes, yielding highly branched Au/liposome hybrid structures. This discrepancy originates from peptide sequence–dependent spatial localization within liposomes. Peptides localized at the membrane interface induce interfacial growth, whereas internally confined peptides promote nucleation within a diffusion‐restricted environment, resulting in spherical nanoparticles. Modulation of membrane composition enables switching of peptide localization, confirming that spatial positioning governs nanoparticle growth. These findings demonstrate that peptide localization acts as a molecular switch governing nanoparticle growth within liposomal nanoreactors.