Synchronised motion of gold nanoparticles in a surfactant-assisted optothermal trap

Surfactants, commonly used to stabilise colloidal suspensions, notably affect the optical trapping of particles. This study focuses on opto-thermal trapping of gold nanoparticles in a surfactant solution, specifically Cetyltrimethylammomium chloride. By creating an optothermal trap with a single drop-casted gold particle at nominal powers, we observed that other particles are trapped at a radial position between 1 and 2 μm. When multiple particles are trapped, their diffusive motion around the centre particle is synchronised. We explore the phenomenon through simulated forces, probing how surfactants influence particle behaviour in optical trapping systems. We further study this trapping behaviour by variations of surfactant concentration, laser power and laser polarisation. We also checked the effect in the presence of different surfactants.