Light-Driven Plasmonic Microrobots for Nanoparticle Manipulation

A recent study published in Nature Communications presents a new microrobotic platform designed to improve the precision and versatility of nanoparticle manipulation using light. Led by Jin Qin and colleagues, the research addresses limitations in traditional optical methods and introduces a microrobot powered by plasmonic nanomotors.

Background: Limitations of Traditional Techniques

Manipulating nanoparticles at the nanoscale is a persistent challenge. Conventional optical tweezers work well for microscale objects but face limitations with nanoparticles due to diffraction limits and limited control over particle orientation. Efforts to induce particle rotation or enhance control often involve trade-offs, such as bulky attachments or complex multi-trap configurations, which restrict flexibility and accuracy.

To overcome these constraints, the authors developed a light-driven microrobotic system—essentially a microdrone that can move with multiple degrees of freedom and manipulate nanoparticles with enhanced precision. This platform aims to provide greater agility and fine-tuned control for applications requiring nanoscale manipulation.

The Current Study

The microrobots were constructed using a rigid, transparent disk-shaped body made from hydrogen silsesquioxane (HSQ), measuring approximately 3.5 μm in diameter and 150 nm in height, with a total weight of around 3.8 pg. Several plasmonic antennas were integrated into the structure to serve as independent motors.

At the core of the manipulation system is a plasmonic nano-tweezer—a gold cross-antenna designed and fabricated using focused helium ion beam milling. This structure generates a localized near-field hot spot that enables the trapping of nanoparticles. The tweezer was embedded directly onto the microrobot in a single fabrication step, with a 1 μm gap maintained between the tweezer and motors to avoid interference.

For experimental validation, a static tweezer setup was used. It was mounted on a coverslip inside a water cell containing nanodiamonds (average diameter of 70 nm). A 980 nm infrared laser was used to create an optical trap, while a 532 nm green laser excited the nanodiamonds’ color centers for fluorescence-based tracking.

The microrobots were released into solution by etching away the indium tin oxide substrate using hydrochloric acid. Once free-floating in water, the infrared laser induced a gentle push from the substrate, enabling the trapping of nanodiamonds without unwanted adhesion, which can result from surface charge effects.

All trapping and manipulation events were recorded using a high-numerical-aperture oil-immersion objective for detailed imaging of microrobot behavior.

Results and Discussion: Performance of the Microrobot Platform

The researchers successfully demonstrated the microrobot’s ability to trap, transport, and release nanoparticles with high precision. Experimental sequences showed the microrobots performing both spiral and linear motion patterns while securely holding nanodiamonds.

Stable trapping was achieved through the interaction of optical gradient forces and plasmonically enhanced fields, confirming the effectiveness of the integrated tweezer design.

The system also exhibited reliable control over dynamic sequences, something not possible with many existing manipulation tools. The applications discussed include targeted drug delivery, quantum sensing, and other nanotech workflows that require cargo transport at the nanoscale.

The authors do acknowledge some limitations. For instance, heat-induced thermophoresis can reduce trapping efficiency, and particles may detach during rapid movement. However, they suggest that implementing an active feedback system could help counteract Brownian motion and improve positional accuracy during manipulation.

With further refinement, this platform could support a wider range of applications in areas like targeted cargo delivery, quantum sensing, and precision nanoscale engineering.

Journal Reference

Qin J., et al. (2025). Light-driven plasmonic microrobot for nanoparticle manipulation. Nature Communications 16, 2570. DOI: 10.1038/s41467-025-57871-x, https://www.nature.com/articles/s41467-025-57871-x