Dynamic Behavior of Noble Metal Nanoparticle Assemblies in Solution

Abstract

Nanoparticle functionalization and assembly is undergoing a period of challenging yet exciting development. Much of this research effort has been focused on the development of new functionalities that might enable strategically-directed assembly of nanoparticles into structures that can be utilized in other important applications.

In order to determine the success of such experiments, researchers often prepare a dried sample and study the assembly patterns with electron microscopy. However, these imaging techniques can be expensive and do not provide a complete illustration of what the three dimensional nanoparticle assemblies truly look like in solution. Moreover, sample preparation presents its own challenges. Most notably, sample preparation may cause alteration to the individual assemblies or unwanted aggregation of the assemblies upon removal of the solution.

To address these concerns, assemblies of anisotropic nanoparticles were tracked free-floating in solution with differential interference contrast (DIC) microscopy. DIC microscopy is an optical technique based on interferometry with high lateral resolution and shallow depth of field. After functionalizing gold and silver nanoparticles for self-assembly, aliquots of the nanoparticle solutions were examined in real-time. Nanoparticle assemblies were observed undergoing rotations, internal vibrations, structural modifications, and interactions with other assemblies. Observations of the dynamic behaviors of nanoparticle assemblies serve as a complement to imaging with electron microscopy and provide new insights into the actual assembly process.