The fast label-free detection of specific antibodies and their concentration in blood plasma is useful for many applications, e.g., in Covid-19 patients. The change in biophysical properties like the refractive index of blood plasma due to the production of antibodies during infection may be very helpful in estimating the level and intensity of infection and subsequent treatment based on blood plasma therapy. In this article, Fano resonance-based refractive index sensor using plasmonic nanomatryoshka is proposed for blood plasma sensing. The interaction between hybridized modes (bright and dark modes) in optimized nanomatryoshka leads to Fano resonance, which by virtue of steeper dispersion can confine the light more efficiently compared with Lorentzian resonance. We propose the excitation of Fano resonances in sub 100-nm size nanomatryoshka based on newly emerging plasmonic materials ZrN and HfN, and one of the most widely used conventional plasmonic material, Au. Fano resonance-based plasmonic sensors leads to sensitivity = 188.5 nm/RIU, 242.5 nm/RIU, and 244.9 nm/RIU for Au, ZrN, and HfN, respectively. The corresponding figure of merit (nm/RIU) is ~ 3.5 \(\times\) 10³, 3.1 \(\times\) 10³, and 2.8 \(\times\) 10³ for Au, ZrN, and HfN, respectively. Present theoretical analysis shows that refractive index sensors with high sensitivity and figure of merit are feasible using Fano modes of plasmonic nanomatryoshka.

特定抗体及其在血浆中浓度的快速无标记检测可用于许多应用，例如在 Covid-19 患者中。由于感染期间抗体的产生而导致的血浆折射率等生物物理特性的变化可能非常有助于估计感染的水平和强度以及基于血浆疗法的后续治疗。在本文中，提出了使用等离子体纳米矩阵的基于 Fano 共振的折射率传感器用于血浆传感。优化的 nanomatryoshka 中的杂化模式（亮模式和暗模式）之间的相互作用导致 Fano 共振，与洛伦兹共振相比，它凭借更陡峭的色散可以更有效地限制光。我们提出了基于新兴等离子体材料 ZrN 和 HfN 以及最广泛使用的常规等离子体材料之一 Au 的亚 100 nm 尺寸 nanomatryoshka 中的 Fano 共振激发。基于 Fano 共振的等离子体传感器对 Au、ZrN 和 HfN 的灵敏度分别为 188.5 nm/RIU、242.5 nm/RIU 和 244.9 nm/RIU。相应的品质因数 (nm/RIU) 约为 3.5 \(\times\)  10 ³ , 3.1  \(\times\)  10 ³和 2.8  \(\times\)  10 ³分别用于 Au、ZrN 和 HfN。目前的理论分析表明，使用等离子纳米矩阵的 Fano 模式，具有高灵敏度和品质因数的折射率传感器是可行的。