Photopyroelectric Tweezers Use Low-Intensity Light to Move Objects

A new photopyroelectric tweezer device (PPT), developed by a team at the Shenzhen Institutes of Advanced Technology of the Chinese Academy of Sciences, enables remote manipulation of objects made from diverse materials, with various geometries, and in different phases. The PPT is a flexible, adaptable object manipulation tool that could have broad use in robotics, biomedicine, and the physical sciences.

Optical tweezers often require a high-intensity laser beam, sophisticated electrode designs, additional electric sources, and low-conductive media, making them impractical for many applications. The PPT device, which combines optical capabilities with electric fields, uses a low-intensity, NIR light to produce a strong driving force for manipulating objects, eliminating the need for a high-intensity laser.

Photopyroelectric tweezers combine the advantages of optical tweezers and electrical fields to enable remote, programmable manipulation of objects with diverse materials, different phases, and various geometries without the need for high-intensity lasers. Courtesy of The Innovation (2024). DOI: 10.1016/j.xinn.2024.100742.

In addition to an NIR spectrum laser light source, the PPT device includes a liquid medium and a photopyroelectric substrate.

The photopyroelectric substrate comprises a superhydrophobic, ferroelectric polymer layer and a lubricant-infused, slippery layer. The polymer layer generates real-time surface charges through a photopyroelectric effect when it is exposed to NIR light. The lubricant layer reduces motion resistance, suppresses contamination, and prevents charge screening by conductive media.

The PPT’s rationally designed structure enables it to efficiently generate robust surface charges when it is exposed to NIR irradiation that is as low as roughly 8.3 mW mm^-2 — that is, when for every square millimeter of area, there are just 8.3 milliwatts of NIR radiation power.

Exposure to NIR light induces a driving force in the PPT of up to roughly 4.6×10^-5 N, or 0.000046 newtons, without the need for a high-intensity laser beam, complex electrode designs, or supplementary electric sources.

“The innovation lies in the rational design of the photopyroelectric substrate, which efficiently generation charges, and the lubricant layer that prevents charge screening by conductive media,” professor Xuemin Du, who led the research, said. “This design imparts unparalleled flexibility and adaptability for diverse object manipulation.”

The PPT enables remote, programmable manipulation of objects made with polymers, metals, and inorganic materials. It can be used to manipulate objects in bubble, liquid, or solid phases and to handle objects with different shapes, like spheres, cuboids, or wires.

The PPT device can be adapted to a conductivity range of 0.001 millisiemens per centimeter to 91.0 millisiemens per centimeter (0.001 mS cm^-1 ~ 91.0 mS cm^-1). It can be used with portable macroscopic manipulation platforms and microscopic manipulation systems with on-demand manipulating areas. It supports on-demand manipulating areas ranging from 5 μm to 2.5 millimeters (mm), enabling cross-scale manipulation of solid objects, liquid droplets, and biological samples ranging from single cells to cell assemblies.

With its flexible, adaptable design, the PPT device has the potential for broad application across numerous fields, including robotics, colloidal science, and biomedical fields such as tissue engineering, neuromodulation, and the study of organoids. It could be used, for example, to manipulate hydrogel robots, sort particles, assemble living cells, manipulate single cells, or stimulate cells.

The PPT surmounts various shortcomings of conventional tweezers and could bridge the gap between macroscopic and microscopic object manipulation. The researchers believe it is a promising new tool for robotics, materials science, and medical research.

The research was published in The Innovation (www.doi.org/10.1016/j.xinn.2024.100742).