Efficiency of Plasmon-Induced Dual-Mode Fluorescence Enhancement upon Two-Photon Excitation

Anisotropic noble metal nanoparticles supporting more than one localized surface plasmon resonance can be tailored for efficient dual-mode fluorescence enhancement by ensuring an adequate coupling to both absorption and emission bands of fluorophores. This approach is naturally extended to two-photon excitation fluorescence, where a molecule is excited by simultaneous nonlinear absorption of two photons. However, the relative impact of plasmon coupling to excitation and emission on the overall fluorescence enhancement can be very different in this case. Here, by using the finite-difference time-domain method, we study the two-photon excitation fluorescence of near-infrared fluorescent protein (NirFP) eqFP670, which is the most red-shifted NirFP to date, in proximity to a silver nanobar. By optimizing the length and aspect ratio of the particle, we reach a fluorescence enhancement factor of 103. We show that the single mode coupling regime with highly tuned near-field significantly outperforms the dual-mode coupling enhancement. The plasmon-induced amplification of the fluorophore’s excitation rate becomes of utmost importance due to its quadratic dependence on light intensity, defining the fluorescence enhancement upon two-photon excitation. Our results can be used for the rational design of hybrid nanosystems based on NirFP and plasmonic nanoparticles with greatly improved brightness important for developing whole-body imaging techniques

Electromagnetic radiation security estimation on the residential building roof for cellular antenna

The work objective is to estimate the electromagnetic environment on the roof where a mobile system base station aerial is installed. The problem arises during maintenance, repair, and assembly operations for antenna-feeder devices. The evaluation problem for ecological assessment of the electromagnetic environment at a standard height of two meters above the roof is solved with the computational prediction method. Two strict models are used for electrodynamic simulation of energy flux density, i.e. a two ray model which describes the plane electromagnetic wave diffraction on the flat perfectly conducting roof surface, and finite models of the roof are described with the canonical problem on a wedge of infinite extent. The difference between the developed model and the known ones lies within the research possibility not only in the computational points but within a whole computational plane. In the simulation process, antenna emission characteristics can be set in a number of ways including those obtained from the radiation object specifications, as it is proposed in a well-known technique. The simulation results for energy flux density distribution in a horizontal plane within the roof space are given. Computational points are placed at the square grid nodes with the period of a quarter wavelength of the transmitter. A physical interpretation of the obtained results is given. A safety conclusion on the human presence on the roof with operating directional cel lular antenna of GSM standard is formulated