Differentiate right and left-handed particles using the force exerted by light

Scanning electron microscope images show D- and L-shaped gold chiral nanoparticles. The inserts visualize three-dimensional patterns of the nanoparticles. Credit: NINS / IMS

Researchers investigated the polarization dependence of the force exerted by circularly polarized light (CPL) by performing optical trapping of chiral nanoparticles. They found that the left and right CPL exerted different strengths of the optical gradient force on the nanoparticles and that the D and L shape particles are subjected to different gradient forces by the CPL. Current results suggest that separation of materials based on their chiral manuality can be accomplished by optical force.

Chirality is the property that the structure is not superimposable on its mirror image. Chiral materials exhibit the characteristic of responding differently to left and right circularly polarized light. When matter is irradiated with a strong laser light, an optical force is exerted on it. It was theoretically expected that the optical force exerted on chiral materials by left and right circularly polarized light would also be different.

The research team at the Institute for Molecular Science and three other universities used an experimental optical trapping technique to observe the strength of the circular polarization-dependent optical gradient exerted on chiral gold nanoparticles. The chiral gold nanoparticles have a D (right) or L (left handed) shape structure and the experiment was performed using both.






The optical force it exerts on the nanoparticle depends on the handiness of the circularly polarized incident light. Credit: NINS / IMS

Although the strength of the optical gradient acting on chiral nanoparticles has been predicted in theory, no observation of the strength has been reported before. The research team was able to observe the strength of the optical gradient originating from chirality (i.e. the difference between the gradient strength of the left and right circularly polarized light), by means of optical trapping of the chiral gold nanoparticles.







Chiral materials exhibit the characteristic of responding differently to left and right circularly polarized light (optical activity). The response of the D-form molecule to left circularly polarized light is the same as that of the L-form molecule to right circularly polarized light and vice versa. Credit: NINS / IMS

The results showed that the strength of the optical gradient was different for the D-shape and L-shape particles.The researchers also found, from the dependence of the force on the wavelength of the light used, that there is a previously unknown effect on the mechanism. of the optical forces dependent on chirality.

Differentiate right-handed and left-handed particles based on the force exerted by light

The graphs are the experimental data and the broken line is the theoretical calculation. The red and blue in the graphs and in the line represent the D-shape and L-shape nanoparticles, respectively. The strength of the optical gradient was different for the D-shape and L-shape particles. Credit: NINS / IMS

The present study elucidated the characteristics of the circular polarization-dependent optical gradient strength on the mechanics of chiral gold nanoparticles. It shows the possibility of separating chiral materials from optical force, which can be accomplished by using locally confined light generated on nanostructures to trap materials and / or by using the optical force of other mechanisms.

The research was published in Science advances.


Chirality-assisted lateral momentum transfer for bi-directional enantioselective separation


More information:
Junsuke Yamanishi et al, Strength of the optical gradient on chiral particles, Science advances (2022). DOI: 10.1126 / sciadv.abq2604. www.science.org/doi/10.1126/sciadv.abq2604

Provided by the National Institutes of Natural Sciences

Citation: Differentiation of right and left hand particles using the force exerted by light (2022, 21 September) recovered on 22 September 2022 from https://phys.org/news/2022-09-differentiating-right-left-handed-particles – exerted .html

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