The behaviour of molecular-plasmonic assemblies in solution
Résumé
he bottom-up approach for making functional nanostructures via self-assembly in solution leads to objects that are usually represented pictorially using idealised models. These models are then validated against experimental observations (microscopy, spectroscopy), often of static nature. As part of our work on plasmonic assemblies, we have been fascinated by the dynamic behaviour of these nano-assemblies in solution, at equilibrium (Brownian fluctuations) and away from equilibrium. These dynamics not only yield information on the shape of the objects in solution (via diffusion and sedimentation), and their evolution over time, but can also help in extracting quantitative spectroscopic data, when coupled to optical spectroscopy.
Fluorescent ligand molecules that bind to the surface of plasmonic particles were found to give insight in dynamics of the molecular capping layer, and show that the gold-thiol bond is not always very robust. These ligand molecules were instrumental in quantifying fluorescence quenching by metal nanoparticles. The optical resonances of the plasmonic particles themselves, which can be read out via light exinction, scattering and intrinsic photoluminescence, also convey information about the structure of particle assemblies, e.g. DNA-linked structures. We furthermore use microfluidic architectures to set up concentration gradients and electric fields, probing the diffusion coefficient and the electrokinetic response of the particles. Using bright-field and dark-field microscopy we can study the dynamics of plasmonic nanoparticle assemblies at the ensemble level and at the single-particle level.