Surface plasmon resonance effect on laser trapping and swarming of gold nanoparticles at an interface

Laser trapping at an interface is a unique platform for aligning and assembling nanomaterials outside the focal spot. In our previous studies, Au nanoparticles form a dynamically evolved assembly outside the focus, leading to the formation of an antenna-like structure with their fluctuating swarms. Herein, we unravel the role of surface plasmon resonance on the swarming phenomena by tuning the trapping laser wavelength concerning the dipole mode for Au nanoparticles of different sizes. We clearly show that the swarm is formed when the laser wavelength is near to the resonance peak of the dipole mode together with an increase in the swarming area. The interpretation is well supported by the scattering spectra and the spatial light scattering profiles from single nanoparticle simulations. These findings indicate that whether the first trapped particle is resonant with trapping laser or not essentially determines the evolution of the swarming.