Nagasue Tomoya, Shinohara Takeha, Hasegawa Seiju, Imura Kohei, Tawa Keiko
Opt Express. 2022 Feb 28;30(5):7526-7538. doi: 10.1364/OE.452468.
A bright spot is observable in the center of Bull's eye plasmonic pattern with a fluorescence microscope due to the plasmonic nanoantenna effect. In this effect, a propagating wave of surface plasmon resonance concentrates in the center. This study focused on the relationship between the center structure of Bull's eye pattern and the nanoantenna effect in four fabricated Bull's eye-type plasmonic chips with centers of different sizes (full- or half-pitch diameter) and shapes (convex or concave). The fluorescence intensity of the fluorescent nanoparticles adsorbed to these plasmonic chips was measured with an upright-inverted microscope to evaluate the plasmonic chip enhancement factor composed of the product of the excitation and emission enhancement and individual factors. When the emission enhancement factor was investigated under nonresonance excitation conditions, by the disappearance of a bright spot, excitation enhancement was found to contribute to the plasmonic nanoantenna effect. The concave Bull's eye structure with a half-pitch diameter demonstrates the highest nanoantenna effect due to the formation of a larger constructive wave in the superposition of the diffraction wave of incident light under resonance conditions. In addition, the electromagnetic field intensity simulated by discrete dipole approximation agrees with the microscopy results. Overall, the results indicate that the plasmonic nanoantenna effect could be controlled depending on the resonance condition and center structure.
由于等离子体纳米天线效应，用荧光显微镜可在靶心等离子体图案的中心观察到一个亮点。在这种效应中，表面等离子体共振的传播波集中在中心。本研究聚焦于四种制作的靶心型等离子体芯片中靶心图案的中心结构与纳米天线效应之间的关系，这些芯片的中心具有不同的尺寸（全间距或半间距直径）和形状（凸形或凹形）。用正置-倒置显微镜测量吸附在这些等离子体芯片上的荧光纳米颗粒的荧光强度，以评估由激发增强和发射增强以及各个因素的乘积组成的等离子体芯片增强因子。在非共振激发条件下研究发射增强因子时，通过亮点的消失发现激发增强对等离子体纳米天线效应有贡献。半间距直径的凹靶心结构由于在共振条件下入射光衍射波叠加中形成更大的相长波，表现出最高的纳米天线效应。此外，通过离散偶极近似模拟的电磁场强度与显微镜结果一致。总体而言，结果表明等离子体纳米天线效应可根据共振条件和中心结构进行控制。
