Turning Plasmonic Antennas on the Right Side: Template Stripping Maximizes Single Molecule Fluorescence Enhancement
Plasmonics is looking for nanogap antennas featuring narrow gap sizes, full accessibility to the plasmonic hotspot and high fabrication throughput. However, the current fabrication methods remain limited to gaps typically around 15-20 nm. Importantly, the plasmonic hotspot is often buried into the structure and not directly accessible for sensing at the antenna surface, thereby limiting the antenna optical performance when it comes to probing molecules.
In a recent Nano Letter article “In-plane plasmonic antenna arrays with surface nanogaps for giant fluorescence enhancement”, we present large arrays of nanoantennas, fabricated by a new approach combining electron beam lithography with planarization, etch back and template stripping. The flat arrays of nanoantennas feature 10 nm gaps with sharp edges and direct surface accessibility of the plasmonic hotspot. This improved nanoantenna fabrication and full access of the hotspot opens up the possibility of fully exploiting the physical properties of plasmonic antennas for a broad range of applications, such as biosensing at membranes or in nanofluidic channels, light harvesting, photocatalysis…
- We demonstrate the superior performance of these surface antennas by probing single fluorescent molecules, and reach huge fluorescence enhancement factors up to 15,000-fold, outperforming previous plasmonic realizations.
- Compared to the previous methods, the combination of back etching with template stripping drastically improves the optical performance of plasmonic nanoantennas by more than one order of magnitude, as we show in a direct comparison with focused ion beam milling.
- Our fabrication approach is fully scalable, with excellent reproducibility, and can be applied to virtually any antenna design.