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

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

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

The researchers investigated the polarization dependence of the force exerted by circularly polarized light (CPL) by performing optical trapping of chiral nanoparticles. They found that left and right CPL exerted different optical gradient force on the nanoparticles, and D and L-shaped particles are subjected to different gradient force by CPL. The present results suggest that the separation of materials according to their chirality can be achieved by the optical force.

Chirality is the property that the structure is not mirror image superimposable. Chiral materials exhibit the characteristic feature that they respond differently to left and right circularly polarized light. When matter is irradiated with strong laser light, optical force is exerted on it. Theoretically, it was expected that the optical force exerted on chiral materials by left and right circularly polarized light would also be different.

The research group from the Institute for Molecular Sciences and three other universities used an experimental optical trapping technique to observe the circular polarization-dependent optical gradient force exerted on chiral gold nanoparticles. Chiral gold nanoparticles are either D-shaped (right) or L-shaped (left), and the experiment was performed using both.

The optical force exerted on the nanoparticle is dependent on the magnitude of the incident circularly polarized light. Credit: NINS/IMS

Although the optical gradient force acting on chiral nanoparticles has been theoretically predicted, no observation of the force has yet been reported. The research group was able to observe the optical gradient force arising from chirality (ie the difference between the gradient force of left and right circularly polarized light) by optical trapping of chiral gold nanoparticles.

Chiral materials have the characteristic feature that they respond 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 optical gradient force was different for the D-form and L-form particles. The researchers also discovered from the dependence of the force on the wavelength of light used, that there is a previously unknown effect on the mechanism of chirality-dependent optical forces .

Differentiate between right and left particles by the force exerted by light

The graphs are the experimental data and the dashed line represents the theoretical calculation. Red and blue in the diagrams and line represent D- and L-form nanoparticles, respectively. The strength of the optical gradient was different for D-form and L-form particles. Credit: NINS/IMS

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

The research was published in Advances in science.


Chirality-assisted lateral momentum transfer for bidirectional enantioselective separation


More information:
Junsuke Yamanishi et al., Optical gradient force on chiral particles, Advances in science (2022). DOI: 10.1126/sciadv.abq2604. www.science.org/doi/10.1126/sciadv.abq2604

Provided by the National Institute of Natural Sciences

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

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