Abstract
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 . 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.
Highlights
IntroductionAlong with advances in tailoring illuminating beams and emitted light as well as synthesis of a variety of fluorescent probes, the fast progress of fluorescence microscopy has been catalyzed by the discovery of the green fluorescent protein and its variants [2]
By using finite-difference time-domain (FDTD) numerical simulations, we show that silver nanobars can be used for efficient fluorescence enhancement of near-infrared fluorescent proteins upon two-photon excitation
The amplified optical near field is localized close to vertices of the nanobar particles upon excitation of both dipole and quadrupole localized surface plasmon resonance (LSPR) modes
Summary
Along with advances in tailoring illuminating beams and emitted light as well as synthesis of a variety of fluorescent probes, the fast progress of fluorescence microscopy has been catalyzed by the discovery of the green fluorescent protein and its variants [2]. These biomolecules, initially found in marine species, are extensively used as genetically encoded fluorescent tags to highlight virtually any protein of interest [3]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
