Plasmonic trapping based on nanoring devices at low incident powers

A plasmonic nanoparticle trap based on an array of nanoring structures with a 160 nm inner disk inside a 300 nm nanohole was demonstrated. Based on the extinction coefficient spectrum, 980 nm incident light was selected to trap 500 nm polystyrene particles. The transmitted intensity was collected for the power spectral density calculation to obtain the corner frequency. Compared to a conventional optical tweezers, approximately 20 times lower incident power is needed for this nanoring device to achieve the same trapping strength. Note from the author: With further experiments, we realized that at a higher incident power (as in the original proceeding, 1.45 mW) two-particle trapping events could happen and result in a higher value for the trap stiffness for the plasmonic tweezers. To eliminate two-particle trapping events, we have applied a lower incident power (0.6 mW) to guarantee single particle trapping and checked images of the trapped particle with a CCD camera. For a proper comparison to conventional optical tweezers, we updated the value of trap stiffness for our plasmonic tweezers for single, 0.5 µm polystyrene particle trapping at low incident power.