This paper reports a narrow Fano resonance of 3D nanocrescent and its application in the label-free detection of single molecules. The Fano resonance depends not only on the gap size but also on the height. The Fano resonance originates from the interference between the quadrupolar mode supported by the horizontal crescent and the dipolar mode along the nanotip. When the height of 3D nanocrescent is 30 nm, the width of Fano resonance is as narrow as 10 nm. The narrow linewidth is caused by the strong narrow resonant absorption coming from the dipolar mode of nanotip overlapping with the quadrupolar mode of nanocrescent, where the absorption spectra are calculated under a horizontal incident light. The narrow Fano resonance is highly sensitive to a single nanoparticle trapped by the nanocrescent. The wavelength shift increases linearly with the refractive index with the relation of Δλ = 22.10n − 28.80, and increases with the size of trapped nanoparticle following a relation of Δλ = 0.826 × r^1.672. These results indicate that if a protein nanoparticle with radius of 2.5 nm is trapped by the nanocrescent, the shift is as large as 4.03 nm.

中文翻译：

---

纳米新月窄法诺共振无标记检测单分子和单纳米粒子的理论研究

本文报道了3D纳米新月的窄Fano共振及其在单分子无标记检测中的应用。法诺共振不仅取决于间隙大小，还取决于高度。法诺共振起源于水平新月支持的四极模式与沿纳米尖端的偶极模式之间的干涉。当3D纳米月牙的高度为30 nm时，Fano共振的宽度窄至10 nm。窄线宽是由纳米尖端的偶极模式与纳米月牙的四极模式重叠产生的强窄共振吸收引起的，其中吸收光谱是在水平入射光下计算的。狭窄的法诺共振对纳米月牙捕获的单个纳米粒子高度敏感。波长偏移随着折射率线性增加，关系式为Δ λ = 22.10 n − 28.80，并且随着捕获的纳米颗粒的尺寸增加，关系式为Δ λ = 0.826 × r ^1.672。这些结果表明，如果半径为 2.5 nm 的蛋白质纳米颗粒被纳米新月捕获，则位移将高达 4.03 nm。