Plasmonic nanoring devices for micro- and nanoparticle trapping and detection using low incident laser powers

摘要

Trapping and detection of micro- and nano-objects at low incident laser powers in the near-infrared region (NIR) is crucial for many biological applications. Using a conventional optical tweezer method, trapping is limited to dielectric particles larger than 100nm in size with high incident laser powers. For this reason, plasmonic nanostructures, which have recently attracted research attentions, offered enhanced trapping fields at their resonant wavelengths, and subsequently can be used to trap and detect silica dielectric particles down to 12nm and single 3.4nm bovine serum albumin proteins using low incident powers (<; 1mW). In this work, we propose a design consisting of nanodisk and nanohole arrays on a 50 nm gold thin film. We demonstrate that this tunable nano-plasmonic device toward the NIR range can improve both the trapping field enhancement and detection of nano-objects using the singular phase drop methods. The tunability of the device was investigated from extinction and reflection spectra while increasing the aperture size in the arrays. The ellipsometric parameters were used to study the dark topologically-protected position, where a rapid change in phase can occur. Our experimental data suggests that, using this abrupt phase change, one can improve the detection sensitivity 10 times compared to the conventional extinction spectra method. In order to investigate the capability of trapping submicron particles with low incident laser powers, we integrated the nano-plasmonic device into a standard optical tweezer system. Stable trapping, with the capability of two-dimensional manipulation of 500 nm fluorescent polystyrene particles over large ranges for seveal minutes, was demonstrated using low incident laser powers of less than 500 μW at 950 nm. The optical trap stiffness and trapping efficiencies of these nanostructured plasmonics devices were experimentally analyzed. The experimental observation shows that stronger optical submicron particle traps can be achieved with approximately 20 times lower incident power when compared to the conventional optical tweezer method.