Boosting Molecular Fluorescence with a Plasmonic Nanolauncher

Molecular emission enhancement is generally obtained by proper coupling with external resonances. Here we propose the idea of a plasmonic nanolauncher, i.e., a metamaterial-inspired ultranarrow channel at cutoff. Its peculiar operation provides uniform phase and drastic amplitude increase all over the channel, allowing high emission enhancement independent of the position of an individual or group of molecules along the channel, and of its length and geometry. This may provide a fascinating mechanism for efficient molecular detection and enhanced optical fluorescence.

Figure 1

Geometry of the structure. Enhanced molecular emission in a plasmonic narrow rectangular channel operating near its cutoff frequency and embedded in a metal-insulator-metal waveguide: (a) front view, (b) side view, (c) perspective.

Figure 2

Simulation results of electric field amplitude sampled at a distance of (a) 10 nm outside the channel exit; (b) inside the channel at a distance of 900 nm from a molecule placed in the middle of the channel of Fig. 1. The black line refers to the scenario of Fig. 1, the blue dotted line to the same geometry but with no side implants, and the red dashed line to the absence of the narrow channel. For this example: $a_{\mathrm{ch}}=20\mathrm{nm}$, $b=200\mathrm{nm}$, $t=300\mathrm{nm}$, $l_{\mathrm{ch}}=2\mu \mathrm{m}$.

Figure 3

Field distribution (snapshot in time) of $E_y$ for a molecule emitting in the center of the narrow channel of Fig. 1 at the cutoff frequency $f_0$ in the three geometries of Fig. 2.

Figure 4

For the same geometry as in Fig. 2a, electric field amplitude sampled at a distance of 10 nm outside of the channel for a collection of nine molecules equispaced inside the narrow channel of Fig. 2. The black dotted line refers to the case in which the molecules are randomly displaced inside the channel.