Embodiments of the present invention relate to methods for preparing high optical density solutions of nanoplates, such as silver nanoplates or silver platelet nanoparticles, and to nanoparticles, solutions and substrates prepared by said methods. The process can include the addition of stabilizing agents (e.g., chemical or biological agents bound or otherwise linked to the nanoparticle surface) that stabilize the nanoparticle before, during, and/or after concentration, thereby allowing for the production of a stable, high optical density solution of silver nanoplates. The process can also include increasing the concentration of silver nanoplates within the solution, and thus increasing the solution optical density.