3D multiple optical trapping of Au-nanoparticles and prokaryote E. coli using intra-cavity generated non-circular beam of inhomogeneous intensity

We report 3D multiple trapping of dielectric polystyrene (PS) beads and gold nano-particles (GNPs) in single beam optical tweezers system using an asymmetric beam of inhomogeneous intensity distribution. This special kind of beam of quasi-TEM11 profile was generated from intra-cavity CW-laser source operating at 532 nm. Multiple trapping of both the low refractive index rod-like Escherichia coli bacteria and 253 nm plasmonic GNPs dispersed in 1.025 μm PS beads which were homogenized in de-ionized water was realized utilizing this spatial beam. Laser-GNPs interaction rendered the enhancement of local surface plasmon resonance field around GNPs causing long-range aggregation of PS beads. The multiple trapping of plasmonic GNPs by the present simple method might find applications for micro- and nano-connectors, underlying physical processes in light-matter interaction assays for inter-particle force analysis, cancer diagnostic and photothermolysis, surface-enhanced Raman scattering (SERS) spectroscopy, and surface plasmon based biological and chemical sensors.