Mao Libang, Cheng Peiyuan, Liu Kuan, Lian Meng, Cao Tun
School of Optoelectronic Engineering and Instrumentation Science, Dalian University of Technology Dalian 116024 China
Nanoscale Adv. 2022 Feb 8;4(6):1617-1625. doi: 10.1039/d1na00764e. eCollection 2022 Mar 15.
Enantioseparation of chiral molecules is an important aspect of life sciences, chemical syntheses, and physics. Yet, the prevailing chemical techniques are not effective. Recently, a few types of plasmonic apertures have been theoretically proposed to distinguish between chiral molecules that vary based on their handedness under circularly polarized illumination. Both analytic calculations and numerical simulation demonstrated that enantioselective optical sieving could be obtained at the nanoscale using a large chiral optical force based on plasmonic resonance enhanced near-field chiral gradients in the aperture. Nevertheless, scaling this scheme to chiral entities of a few nanometer size (, proteins and DNA) faces formidable challenges owing to the fabrication limit of a deeply sub-nanometer aperture and the intense power levels needed for nanoscale trapping. In contrast, by extending the Friedrich-Wintgen theory of the bound states in the continuum (BIC) to photonics, one may explore another mechanism to obtain enantioselective separation of chiral nanoparticles using all-dielectric nanostructures. Here, we present a metasurface composed of an array of silicon (Si) nanodisks embedded with off-set holes, which supports a sharp high-quality () magnetic dipolar (MD) resonance originating from a distortion of symmetry-protected BIC, so called quasi-BIC. We, for the very first time, show that such a quasi-BIC MD resonance can markedly improve the chiral lateral force on the paired enantiomers with linearly polarized illumination. This quasi-BIC MD resonance can enhance the chirality density gradient with alternating sign at each octant around the Si nanodisk, while exhibiting a small gradient for the electromagnetic (EM) density. This offers a chiral lateral force that is 1 order larger in magnitude compared to the non-chiral lateral forces on sub-2 nm chiral objects with a chirality parameter of ±0.01. Moreover, the quasi-BIC MD resonance can excite four pairs of diverse optical potential wells (-13 ) that are distributed uniformly along the outer edge of the resonator, enabling a simultaneous separation of four paired enantiomers. Our proposed dielectric metasurface may move forward the techniques of enantioseparation and enantiopurification, taking a novel perspective to advanced all-optical enantiopure synthesis.
手性分子的对映体分离是生命科学、化学合成和物理学的一个重要方面。然而，目前流行的化学技术并不有效。最近，理论上提出了几种类型的等离子体孔径，用于区分在圆偏振光照下基于其手性而变化的手性分子。解析计算和数值模拟均表明，利用基于孔径中等离子体共振增强的近场手性梯度产生的大手性光学力，可以在纳米尺度上实现对映选择性光学筛分。然而，由于深亚纳米孔径的制造限制以及纳米尺度捕获所需的高功率水平，将该方案扩展到几纳米尺寸的手性实体（如蛋白质和DNA）面临巨大挑战。相比之下，通过将连续介质束缚态（BIC）的弗里德里希 - 温特根理论扩展到光子学领域，人们可以探索另一种机制，利用全介质纳米结构实现手性纳米颗粒的对映选择性分离。在此，我们展示了一种由嵌入偏置孔的硅（Si）纳米盘阵列组成的超表面，它支持一种尖锐的高品质（）磁偶极（MD）共振，该共振源于对称保护的BIC的畸变，即所谓的准BIC。我们首次表明，这种准BIC MD共振在线偏振光照下能显著提高对映体对的手性横向力。这种准BIC MD共振可以增强围绕Si纳米盘每个卦限处具有交替符号的手性密度梯度，而电磁（EM）密度梯度较小。这提供了一种手性横向力，与手性参数为±0.01的亚2纳米手性物体上的非手性横向力相比，其大小要大1个数量级。此外，准BIC MD共振可以激发四对不同的光学势阱（-13 ），它们沿谐振器外边缘均匀分布，能够同时分离四对对映体。我们提出的介电超表面可能会推动对映体分离和对映体纯化技术的发展，为先进的全光对映体纯合成提供新的视角。
