We also find that the enhancement of RET rate in the single nanorod structure decreases when the donor and acceptor have nonparallel selleck chemicals dipole moment directions. We then propose simple V-shaped nanorod structures for a donor-acceptor LEE011 supplier pair with nonparallel dipole moments. We find that these structures can lead to a remarkable resonance energy transfer enhancement ten times larger than

that by the single nanorod structure. We demonstrate that the enhancing effect by these structures can be controlled by the nanorod length of the branch in the V-shaped structure and that these structures are robust regardless of the shape and material of the corner part. This controllability and robustness are also preserved for donor-dipole pair with asymmetric configuration. Therefore, these structures can be applied in integrated

photonic devices. Methods Without the loss of generality, we quantify the enhancement of RET by the normalized energy transfer rate (nETR), which means that the RET rate normalized to the case in vacuum. The nETR is given as [32, 33] (1) where n A and n D are the unit vectors along the directions of the dipole moments of the acceptor and donor, respectively, ω is the transition frequency, G(r A , r D , ω) is the dyadic Green’s function [34], E D (r A , ω) is the electric field at the position SN-38 mouse of the acceptor induced by the donor dipole in the presence of the plasmonic structures, while G vac(r A , r D , ω) and E D,vac(r A , ω) correspond to the case in vacuum but without the plasmonic Progesterone structures.

The calculations of the electric field induced by the dipole are performed by the finite element method with the commercial COMSOL Multiphysics software. All metal structures in this paper are set to be silver; the electric permittivity of silver is gathered by fitting the experimental data of Johnson and Christy with piecewise cubic interpolation [35]. All nanostructures are set on a semi-infinite SiO2 substrate with the refractive index of 1.456, and the surrounding medium is air. Results and discussion Firstly, we consider single Ag nanorod structures with different cross sections. The schematic pictures of the single nanorod structures and their cross sections are shown in Figure 1a,b. The donor and acceptor dipoles are both aligned to the center axis of the nanorod at different ends, the distance from each dipole to the end of the nanorod is d = 20 nm, and the longitudinal length of the nanorods is set to L = 250 nm. Notice that the longitudinal surface plasmon resonance modes of the nanorods are responsible for the enhancement of the RET rate; in order to compare the ability of different nanorods to enhance the RET, we tune the parameters a, r, and w to make the resonance frequencies of their longitudinal surface plasmon modes approximately equal.