Enantioselective optical trapping of chiral nanoparticles using a transverse optical needle field with a transverse spin

Abstract

Since the fundamental building blocks of life are built of chiral amino acids and chiral sugar, enantiomer separation is of great interest in plenty of chemical syntheses. Light-chiral material interaction leads to a unique chiral optical force, which possesses opposite directions for specimens with different handedness. However, usually the enantioselective sorting is challenging in optical tweezers due to the dominating achiral force. In this work, we propose an optical technique to sort chiral specimens by use of a transverse optical needle field with a transverse spin (TONFTS), which is constructed through reversing the radiation patterns from an array of paired orthogonal electric dipoles located in the focal plane of a 4Pi microscopy and experimentally generated with a home-built vectorial optical field generator. It is demonstrated that the transverse component of the photonic spin gives rise to the chiral optical force perpendicular to the direction of the light’s propagation, while the transverse achiral gradient force would be dramatically diminished by the uniform intensity profile of the optical needle field. Consequently, chiral nanoparticles with different handedness would be laterally sorted by the TONFTS and trapped at different locations along the optical needle field, providing a feasible route toward all-optical enantiopure chemical syntheses and enantiomer separations in pharmaceuticals.

Enantioselective Optical Trapping of Multiple Pairs of Enantiomers by Focused Hybrid Polarized Beams

“…[9] Compared to CD and complex chemical methods, [10][11][12] optical force-based methods with less invasiveness and higher efficiency have developed into a topic of active research. [13][14][15][16][17][18][19][20][21][22][23][24][25] There are many methods to generate the optical forces related to chirality, including the chirality-dependent lateral optical forces (LOFs) emerging from the interaction of the spin angular momentum with chiral particles, [13,14] the optical chiral forces induced by circularly polarized beams [16,21] and vector beams. [17,18,20] Especially, the optical enantioselective trap allows to simultaneously confine a pair of enantiomers of opposite chirality at two different positions, achieved by beams of radially varying polarization states [18] and vector Lissajous beams.…”

Optical tweezing chiral particles with 3D structured light

“…The potential of sorting enantiomers using an all-optical method would have a profound impact on the drug and pharmaceutical industries, and as such there has been a substantial number of studies looking at enantioselective trapping schemes. These have predominantly involved using an unstructured laser source [8][9][10][11] and/or plasmonic enhancement systems [12][13][14][15][16][17][18][19][20][21][22][23][24] , though there have been a handful of studies employing structured light 20,[25][26][27][28][29] . Optical vortices are inherently chiral, their OAM per photon is where  is known as the topological charge.…”

Nano-particle transport and the prediction of a valid area to be trapped based on a plasmonic antenna array

“…19 In recent years, several studies have demonstrated the promise of plasmonic optical trapping and transport. [20][21][22] For example, Kai Wang and his colleagues had proposed a method to trap and rotate the nanoparticles. In his letter, although the gold pillars can be used to trap and rotate the nanoparticles, but the nanoparticles just rotate around the gold pillars, not a long distance transport.…”