Plasmonic‐Hydrogel Hybrid Biomaterials via In Situ Seeded Growth

The combination of hydrogels and functional plasmonic metal nanoparticles affords the development of unique hybrid systems, such as actuators, biosensors, and drug delivery systems, among others. Being typically prepared in colloidal suspension, incorporating shape‐controlled plasmonic nanoparticles on polymer substrates typically requires lengthy processes involving synthesis, washing, and self‐assembly. We report an alternative, robust in situ seed‐mediated growth method, whereby either isotropic or anisotropic Au and Ag nanoparticles can be prepared directly on gelatin‐based hydrogels, taking advantage of the polymer’s native chemical functionalities. In‐depth characterization of gold precursor ‐ polymer interactions enabled the rational growth of branched gold nanoparticles on biocompatible hydrogels with different physicochemical properties. In situ seeded growth circumvents traditional limitations imposed by the need of colloidal stability, thereby enabling gold nanoparticle synthesis under surfactant‐free conditions and in high ionic strength solutions, thus enhancing their suitability for applications with live cells. This method can be expanded to create libraries of hybrid plasmonic materials with potential impact in the fabrication of functional 3D cell culture substrates, as well as biological and chemical sensors.