A revisitation of the Forster energy transfer near a metallic spherical nanoparticle: (1) Efficiency enhancement or reduction? (2) The control of the Forster radius of the unbounded medium. (3) The impact of the local density of states
A revisitation of the Forster energy transfer near a metallic spherical nanoparticle: (1) Efficiency enhancement or reduction? (2) The control of the Forster radius of the unbounded medium. (3) The impact of the local density of states
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DOI：
10.1063/1.4847875
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发表时间：
2013-12-28
影响因子：
4.4
通讯作者：
Zurita-Sanchez, Jorge R.
中科院分区：
文献类型：
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作者：
Alejandro Gonzaga-Galeana, J.;Zurita-Sanchez, Jorge R.
这一理论回顾的中心动机来自这样一个事实，即一些关于福斯特能量转移的实验工作报告了当供体-受体分子对靠近金属粒子时，福斯特效率有所提高，而另一些则发现效率下降。在纳米级金属球存在的情况下，我们计算了固定供体位置的福斯特能量传递率K-F和福斯特效率eta作为受体位置r(a)的函数的等高线图。这些等高线图清楚地突出了球对K-F和eta作为供体位置的影响，供体和受体偶极子的取向，以及颗粒大小的变化；此外，表面等离子激元激发对K-F（r(A)）和eta的影响也很容易从这些等高线图中看出。此外，在特定的给体-受体空间分布、不同的颗粒尺寸和不同的分子偶极子取向下，我们得到了对给体-表面分离的增强因子K-F/K-F0 （K-F0是指没有球体的情况）。因此，我们的计算提供了在金属纳米球存在下的福斯特能量传递的系统分析。基于这些结果，我们提出假设来解释上述关于eta的相互矛盾的实验结果。为了补充我们的研究，我们研究了态的局部密度对K-F的影响。当分子间分离R小于或接近3 nm时，K-F几乎不受球体的扰动，因为直接的给体-受体电磁相互作用占主导地位。相反，当R大于或接近3 nm时，纳米球会扰动K-F，并且如果激发等离子共振，这种扰动会更强。K-F/K-F0在某些区域可以大大提高，但这些区域与低效率区域重合，影响涉及福斯特工艺的应用。在纳米球存在的情况下，高福斯特效率区（>= 0.5）的形状与无球时相同，但其扩展范围（福斯特半径r - 0）减小；这种效应是供体直接衰变率大幅增加的结果，而R-o在很大程度上取决于供体位置。因此，球体控制着与无界介质对应的效率模式相关的R-o；这种效应可以在基于荧光共振能量转移的纳米级蛋白质位移测量技术中得到利用。K-F（rho）的功能形式由分子间分离R、分子对的空间构型和偶极子取向以及供体与纳米粒子的接近度决定。(C) 2013 AIP出版有限责任公司
The central motivation of this theoretical revisitation comes from the fact that some experimental works about Forster energy transfer report improvement of the Forster efficiency when the donor-acceptor molecular pair is in the vicinity of a metallic particle, while others found efficiency deterioration. In the presence of a nanoscale metallic sphere, we calculate contour plots of the Forster energy transfer rate K-F and the Forster efficiency eta as a function of the acceptor position r(A) for a fixed donor position. These contour plots clearly highlight the influence of the sphere on K-F and eta as the donor position, the orientations of donor and acceptor dipoles, and the particle size are varied; also the impact on K-F(r(A)) and eta due to the excitation of surface plasmons is easily noticeable from these contour plots. Moreover, we obtain the enhancement factor K-F/K-F0 (K-F0 refers to the case without sphere) against the donor-surface separation for particular donor-acceptor spatial distributions, several particle sizes, and distinct molecular dipole orientations. Therefore, our calculations provide a systematic analysis of the Forster energy transfer in the presence of a metallic nanosphere. Based on these results, we formulate hypotheses for explaining the aforementioned contradictory experimental results about eta. To complement our study, we examine the impact of the local density of states rho on K-F. K-F is practically unperturbed by sphere when the intermolecular separation R is less than or similar to 3 nm, since the direct donor-acceptor electromagnetic interaction is dominant. On the contrary, when R greater than or similar to 3 nm, the nanosphere perturbs K-F and this perturbation is stronger if plasmonic resonances are excited. K-F/K-F0 can greatly be enhanced in certain regions, but these regions coincide with low-efficiency regions, compromising applications involving the Forster process. In the presence of the nanosphere, the high Forster efficiency region (eta >= 0.5) has the same shape as that for the case without sphere, but its extension (Forster radius R-o) is reduced; this effect is a consequence of the large increase of the donor direct decay rate and R-o depends strongly on donor position. Consequently, the sphere controls R-o that is associated with the efficiency pattern that corresponds to the unbounded medium; this effect can be exploited in the measuring technique of nanoscale displacements of proteins that is based on the fluorescence resonant energy transfer. The functional form of K-F(rho) is determined by the intermolecular separation R, the spatial configuration and the dipole orientations of the molecular pair, and the donor proximity to the nanoparticle. (C) 2013 AIP Publishing LLC.