Field-directed Self-assembly of Multifunctional Magnetic-Plasmonic Core-shell Nanoparticles with Applications to Photonics

X. Xue, K. Liu, J. Wang, E.P. Furlani
University at Buffalo - SUNY,
United States

Keywords: field-directed self-assembly, core-shell nanoparticles, magnetic dipole-dipole interactions, mangetic-plasmonic and sensing application


Interest in the manipulation and self-assembly of magnetic nanoparticles has grown in recent years due to advances in particle synthesis and functionalization, which have led to a proliferation of applications that include the biomolecular transport, drug targeting, gene transfection, bioseparation, microfluidic mixers and bio and chemical sensors, among others. However, despite the growing application of magnetic nanoparticles, many fundamental aspects of their collective behavior remain unknown. In this presentation, we use computational modeling to demonstrate the self-assembly of magnetic core-shell particles into chain structures and the control of this process by carefully choosing particle properties and an applied field. Our analysis takes into account several competitive effects, including the induced magnetic dipole-dipole interactions, the electrostatic repulsion between particles due to the double layer forces based on DLVO theory, Brownian dynamics, Van der Waals interaction and a steric repulsive force caused by surfactant-surfactant contact. The model is used to study the self-assembly (chaining) of magnetic-plasmonic Fe3O4@Au core-shell nanoparticles that are confined to a nanochannel. Computational photonic analysis is used to compute the optical behavior of 1D multiparticle chains. We show that the plasmonic resonance (absorption spectrum) of the chain shifts to longer wavelengths as the number of chained nanoparticles increases. The peak resonant wavelength of a finite chain will asymptotically approach that of an infinite chain as the number of nanoparticles increases, with a relatively small change when the number of particles is over 8. An analysis is also performed to study the local profiles of thermal loss and electric field enhancement. The results show a relatively uniform distribution of the thermal loss and highly localized electric field hot spots with an enhancement factor over 200 between adjacent nanoparticles. The ability to self-assemble the particles with tunable field enhancement holds potential for fundamental studies of light-matter interactions as well as applications of bio and chemical sensing.