Zhao Yang, Saleh Amr A E, van de Haar Marie Anne, Baum Brian, Briggs Justin A, Lay Alice, Reyes-Becerra Olivia A, Dionne Jennifer A
Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA.
Department of Engineering Mathematics and Physics, Faculty of Engineering, Cairo University, Giza, Egypt.
Nat Nanotechnol. 2017 Nov;12(11):1055-1059. doi: 10.1038/nnano.2017.180. Epub 2017 Sep 25.
Circularly polarized light (CPL) exerts a force of different magnitude on left- and right-handed enantiomers, an effect that could be exploited for chiral resolution of chemical compounds as well as controlled assembly of chiral nanostructures. However, enantioselective optical forces are challenging to control and quantify because their magnitude is extremely small (sub-piconewton) and varies in space with sub-micrometre resolution. Here, we report a technique to both strengthen and visualize these forces, using a chiral atomic force microscope probe coupled to a plasmonic optical tweezer. Illumination of the plasmonic tweezer with CPL exerts a force on the microscope tip that depends on the handedness of the light and the tip. In particular, for a left-handed chiral tip, transverse forces are attractive with left-CPL and repulsive with right-CPL. Additionally, total force differences between opposite-handed specimens exceed 10 pN. The microscope tip can map chiral forces with 2 nm lateral resolution, revealing a distinct spatial distribution of forces for each handedness.
圆偏振光（CPL）对左旋和右旋对映体施加不同大小的力，这种效应可用于化合物的手性拆分以及手性纳米结构的可控组装。然而，对映选择性光学力难以控制和量化，因为它们的大小极小（亚皮牛顿）且在空间中以亚微米分辨率变化。在此，我们报告一种技术，通过将手性原子力显微镜探针与等离子体光镊耦合，既能增强这些力又能使其可视化。用CPL照射等离子体光镊会对显微镜尖端施加一个取决于光的手性和尖端手性的力。特别是，对于左旋手性尖端，横向力在左旋CPL作用下是吸引性的，在右旋CPL作用下是排斥性的。此外，相反手性样本之间的总力差超过10 pN。显微镜尖端可以以2 nm的横向分辨率绘制手性力，揭示每种手性力的独特空间分布。
