Abstract
Optical manipulation of gold nanoparticles has facilitated a wide range of innovative science and applications such as nanothermometry, cell poration, optical binding and optomechanics, with many exploiting the surface plasmon resonance. However, conventional gold nanoparticles usually depart from spherical shape and typically exhibit icosahedron, decahedron, triangular or hexagonal prism, thus making such studies less controlled and leading to potential artefacts in trapping behaviour. We successfully synthesise ultrasmooth gold nanoparticles of 50nm and 100nm in diameter with an improved monodispersity both in shape and size compared to conventional gold nanoparticles. We demonstrate the first optical manipulation of such ultrasmooth gold nanoparticles in a near infrared optical trap, and show trap stiffness with up to a three-fold reduction in standard deviation both in liquid and air, compared to conventional gold nanoparticles. Our trapping study highlights the exceptional sensitivity of the trapping parameters of gold nanoparticles on their morphology. Furthermore, we for the first time quantify the particle temperature of airborne gold nanoparticles for a range of optical powers based on the trap stiffness measurements and reveal the effects of particle morphology. We show our ultrasmooth gold nanoparticles exhibit lower temperature than the conventional counterparts due to the lack of additional morphological features that induce plasmonic heating. The use of ultrasmooth gold nanoparticles can pave the way for more controlled studies of optical binding and plasmon mediated light-matter interactions and novel applications in optomechanics such as optically controllable nanoprobes of weak forces and torques.
