Ultimate capabilities of sharp metal tips for plasmon nanofocusing, near-field trapping and sensing

This Letter considers an ‘ultimate’ nanofocusing system with arguably the largest field enhancements achievable in plasmonic nanofocusing structures. These enhancements appear far beyond those required for single molecule detection. The proposed structure is demonstrated to be ∼4 orders of magnitude more efficient for trapping of small nanoparticles and single molecules, than the tip-assisted trapping. It does not require direct irradiation of the tip, and this will enable highly targeted delivery of the optical energy to nanoscale regions as small as a few nanometers (e.g., inside living cells) for trapping, imaging, localized heat discharge, and superior sensing in a new generation of nano-optical detectors.

► We analyze a nanofocusing structure with the largest achievable field enhancement.
► We show high efficiency of the structure for near-field trapping and manipulation.
► We discuss applications for nano-optical sensors and monitoring techniques.
► We demonstrate the capabilities for single-molecule detection and imaging.
► We present detailed physical interpretation of the obtained results.