Highly tunable plasmonic nanoring arrays for nanoparticle manipulation and detection.

The advancement of trapping and detection of nano-objects at very low laser powers in the near-infra-red region (NIR) is crucial for many applications. Singular visible-light nano-optics based on abrupt phase changes have recently demonstrated a significant improvement in molecule detection. Here, we propose and demonstrate tunable plasmonic nanodevices, which can improve both the trapping field enhancement and detection of nano-objects using singular phase drops in the NIR range. The plasmonic nanostructures, which consist of gaps with dimensions 50 nm × 50 nm connecting nanorings in arrays is discussed. These gaps act as individual detection and trapping sites. The tunability of the system is evident from extinction and reflection spectra while increasing the aperture size in the arrays. Additionally, in the region where the plasmonic nano-array exhibits topologically-protected, near-zero reflection behaviour, the phase displays a rapid change. Our experimental data predict that, using this abrupt phase changes, one can improve the detection sensitivity by 10 times compared to the extinction spectra method. We finally report experimental evidence of 100 nm polystyrene beads trapping using low incident power on these devices. The overall design demonstrates strong capability as an optical, label-free, non-destructive tool for single molecule manipulation where low trapping intensity, minimal photo bleaching and high sensitivity is required.