© 2016 American Chemical Society. Silver nanoparticles have been of great interest as plasmonic substrates for sensing and imaging, catalysts, or antimicrobial systems. Their physical properties are strongly dependent on parameters that remain challenging to control such as size, chemical composition, and spatial distribution. We report here on supramolecular assemblies of a novel peptide amphiphile containing aldehyde functionality in order to reduce silver ions and subsequently nucleate silver metal nanoparticles in water. This system spontaneously generates monodisperse silver particles at fairly regular distances along the length of the filamentous organic assemblies. The metal-organic hybrid structures exhibited antimicrobial activity and significantly less toxicity toward eukaryotic cells. Metallized organic nanofibers of the type described here offer the possibility to create hydrogels, which integrate the useful functions of silver nanoparticles with controllable metallic content.