Colloidal Dynamics in Evanescent Optical Fields

Abstract

Reversible particle assemblies are of great interest to researchers working in the fields of nanotechnology, biochemistry and materials science. Assemblies of nanoparticles have been achieved using surface plasmon excitations facilitated by evanescent illumination. Such mechanisms utilise the plasmon-mediated heat to drive fluid flow, which leads to par- ticle accumulation. In this thesis, we study in detail to decouple the effects of these fields and forces involved in the formation of large-scale nanoparticle assemblies. We quantify and draw a contrast between the role of optical (plasmonic) and fluidic fields, showing the dominance of fluidic effects by a huge margin. Once their significance and strength are established, we add a component of an even stronger field called the thermoelectric field, facilitated by the addition of an electrolyte, which generates an electric field under tem- perature gradients. We compare the assemblies formed with only the plasmofluidic field and that, in the presence of thermoelectric fields and demonstrate a multifold intensity en- hancement in the latter case. This work will have applications in studying scattered light signatures from highly scattering particle assemblies and biosensing, like SERS, at rela- tively lower powers. Experimental observations are accompanied by extensive simulation analysis in finite element method-based COMSOL.