Light Emitting Diode Irradiation Can Control the Morphology and Optical Properties of Silver Nanoparticles

A facile method for the preparation of silver nanoparticles (AgNPs) of various sizes and morphologies, including dodecahedra, nanorods, and nanoplates, has been discovered. By choosing the desired optical properties (absorption maximum) and irradiating spherical AgNP seeds with a selected light emitting diode, we achieve control over the size, morphology, and optical properties. The properties of AgNPs are intrinsically dependent on the size and shape of the particles, which can be readily controlled with the strategies reported here. Literature methods for the synthesis of anisotropic AgNPs require complex solutions containing seed nanoparticles with specific twinning defects, and a variety of specific stabilizing ligands direct the growth of the seeds but limit the versatility of the particles. In general, these thermal routes to anisotropic AgNPs give particles with high polydispersity, limiting their applications in single molecule spectroscopy and surface plasmon resonance spectroscopy. We describe a single photochemical method for preparation of AgNPs with predictable and controllable size and morphology that are produced from a single source of photochemically grown AgNP seeds stabilized only by sodium citrate. We also describe a common mechanism for the formation of the various types of AgNPs.