Plasmonic optical nano-antennas for total internal reflection fluorescence microscope

Abstract

Plasmonic nano-antennas have been taking a crucial position in biophysical or chemical applications such as fluorescence microscopy or surface enhanced Raman spectroscopy. We have designed and simulated a gold nano-antenna active in optical frequency range, using the finite-difference time-domain method. Employing the fundamental and higher-order resonant modes at the same time, both excitation and decay rate of a quantum emitter can be highly increased at the central gap of the antenna. Taking advantage of barely interrupting pumping and probing channels, excitation source can be incident in oblique angles from the substrate while the radiation from the emitter can be collected at the upper medium. When the angles are larger than the critical angle of the total internal reflection, a high signal-to-noise ratio is achievable by completely reflecting the incident lights not coupled to the antenna mode. Our designed antenna can also satisfy diverse experimental conditions for flexible tunability in resonant wavelength range and field enhancement by adjusting geometrical dimensions. For example, the resonant wavelengths of the first mode for the fluorescence signal and the third mode for the excitation signal are tuned up to 400 and 100 nm ranges respectively. We expect that the proposed plasmonic antenna would improve the degree of signal enhancement and quality in total internal reflection fluorescence microscopy. In addition, we have also investigated platinum nano-rod antennas formed by electron beam induced deposition.