In a groundbreaking advancement poised to reshape nanotechnology and molecular manipulation, researchers from Tokyo University of Science (TUS), Institute for Molecular Science (IMS), and Seoul National University (SNU) have unveiled a pioneering method to selectively control the movement of chiral nanoparticles using light. This innovative approach employs circularly polarized light guided through ultra-thin optical nanofibers, harnessing the evanescent field to exert directional forces on nanoparticles based on their chirality—effectively sorting them by their handedness at the nanoscale.
Chirality, a fundamental geometric property where objects are not superimposable on their mirror images, penetrates numerous realms of science, particularly in chemistry and biology. Molecules such as amino acids—essential to life—exhibit chirality, and their handedness dramatically influences biochemical interactions. Previously, sorting chiral microscale particles using circularly polarized light was feasible but extending this capability down to the nanometer scale remained an elusive challenge, largely due to diminishing light-matter interaction forces juxtaposed with overwhelming thermal motion at such small scales.
The investigators circumvented these limitations by exploiting the evanescent field generated by light confined within an optical nanofiber. Unlike conventional light beams, this evanescent field exists just outside the surface of the fiber and decays exponentially with distance, providing a highly localized and intensified electromagnetic environment. Upon illuminating the nanocubes with circularly polarized light circulated through these fibers, the researchers observed directional propulsion influenced by the interplay between the light’s polarization and the nanoparticle’s chirality.
Metallic nanocubes fabricated with precisely twisted faces—imparting them with defined chiral geometries—served as the experimental subjects. When positioned near the nanofiber’s surface, these particles exhibited movement along the fiber axis. Crucially, the direction and velocity of their travel depended on whether the particle was left- or right-handed and on whether the light’s circular polarization rotated clockwise or counterclockwise. By toggling the polarization, the researchers managed to reverse the movement of nanoparticles selectively, effectively creating a light-actuated sorting mechanism.
Such a demonstration marks a critical leap beyond prior methodologies that were successful only at micrometer scales—roughly thousands of times larger than the nanoparticles targeted here. The team’s experiments revealed that the momentum transfer from the tightly confined circularly polarized light produces a chiral-selective optical force sufficiently robust to overcome random Brownian motion. This clarity in directional transport at the nanoscale paves the way for novel manipulation techniques of chiral molecular systems.
Professor Mark Sadgrove of TUS, who led the optical fiber technique development, expressed astonishment at the pronounced effects observed in raw experimental data. The implementation of ultra-thin optical fibers rendered a localized electromagnetic field intense enough to discriminate handedness in nanoparticles, underscoring the promise of nanofiber platforms in precision optical manipulation.
This breakthrough holds profound implications not only for fundamental science but also for applied fields such as pharmaceutical chemistry, where distinguishing and isolating enantiomers—the left- and right-handed forms of chiral molecules—remains essential due to their drastically different biological activities. Traditional chemical methods for enantiomer separation are often complex and inefficient; optical sorting at the nanoscale could revolutionize such processes by providing a non-invasive, rapid, and highly selective alternative.
Furthermore, the researchers envision scaling down the approach to interact with particles approximately ten to a hundred times smaller than those currently tested. Success in this miniaturization would open new vistas in molecular-scale manipulation, allowing direct optical control over individual chiral molecules. This capability could transform studies in molecular biology, materials science, and nanomedicine by enabling targeted sorting, assembly, or modification of molecular structures based on chirality.
The collaborative nature of the study epitomizes multidisciplinary synergy across physics, chemistry, and engineering. The nanocubes were meticulously crafted at IMS under Dr. Hyo-Yong Ahn’s guidance, while optical techniques were refined at TUS. Contributions from Prof. Ki Tae Nam’s team at SNU enriched the chiral nanoparticle design, and expertise from Prof. Hiromi Okamoto’s group at IMS elucidated the intricate optical properties underpinning the observed phenomena.
Thermal fluctuations at the nanoscale typically dwarf the forces imparted by light, presenting a significant hurdle for optical manipulation. By leveraging the evanescent field in proximity to optical nanofibers, the researchers amplified the electromagnetic interactions while confining the effect spatially, effectively enhancing the signal-to-noise ratio and enabling reliable directionality of particle transport contingent on chirality.
This research not only advances nano-optics but also extends the horizon for photonics in practical applications. The possibility to guide nanoparticles along predetermined paths with tunable velocity and directionality through light polarization control sets a foundation for integrating optical sorting in lab-on-a-chip devices, targeted drug delivery, and nanoscale assembly systems.
In essence, the study demonstrates a compelling synergy between light’s angular momentum in circular polarization and chiral geometry at the nanoscale, translating subtle physical principles into actionable control mechanisms. Continued exploration of this phenomenon could catalyze the development of sophisticated techniques to probe and manipulate the molecular underpinnings of life and materials science alike.
As the researchers refine the sensitivity and scalability of this optical transport mechanism, the implications for separating and studying chiral molecules grow ever more promising. This breakthrough represents a harbinger of future technologies where light’s polarization states become tools not just for illumination or signal transmission, but for precision engineering and manipulation of the molecular world.
Subject of Research: Not applicable
Article Title: Chirality-selective optical transport of nanoparticles in the evanescent field of a nanofibre
News Publication Date: 16-Apr-2026
References: DOI: 10.1038/s41467-026-71585-8
Image Credits: Dr. Mark Sadgrove from Tokyo University of Science, Japan
Keywords
Nanotechnology, Optics, Photonics, Applied physics, Optical materials, Nanoparticles, Materials science, Chemistry, Biophysics
