Opto-thermoelectric nanotweezers (OTENTs) have been developed that use light at the nanoscale to manipulate metal nanoparticles in a wide range of materials, sizes, and shapes, with single-particle resolution. OTENTs could open new possibilities for the use of nanophotonics in mobile technology and other fields. The research team from the University of Texas at Austin took advantage of optical heating arising from photon-to-phonon conversion to create the extremely low-power optical tweezing technique. Researchers optically heated a thermoplasmonic substrate, which generated a light-directed thermoelectric field, allowing them to manipulate particles at the nanoscale. When used in combination with dark-field optical imaging, OTENTs can selectively trap nanoparticles and their spectroscopic response can be resolved in situ. The research was led by professor Yuebing Zheng’s group in mechanical engineering, which discovered a way to manipulate individual nanoparticles and nanowires. A group led by chemical engineering professor Brian Korgel synthesized the nanowires so they could be used in experiments. Physics professor Ernst-Ludwig Florin and researcher Emanuel Lissek performed precise measurements to demonstrate the strength of OTENTs. Cooperation among nanophotonics, nanochemistry, and nanophysics researchers thus provided the tools to manipulate and analyze nanoparticles in new ways. “Until now, we simply did not know how to manipulate nanoparticles using optical heating,” said Zheng. The nanotweezers are applicable to a wide range of metal, semiconductor, polymer, and dielectric nanostructures with charged or hydrophobic surfaces. Thus far, researchers have successfully trapped silicon nanospheres, silica beads, polystyrene beads, silicon nanowires, germanium nanowires, and metal nanostructures. Researchers believe that further arrangement of these nanomaterials in a rationally designed manner could lead to a better understanding of how matter organizes and to the potential discovery of new functional materials. In a biological setting, Zheng believes that live-cell manipulation and cell-to-cell communication could be a primary research focus for engineers wishing to exploit the capabilities afforded by OTENTs. “Optimization of the current system to make it biocompatible is the next step of our project. We expect to use our tweezers to manipulate biological cells and molecules at single-molecule resolution, to control drug release, and to study the cell-cell interaction. The manipulation and analysis of biological objects will open a new door to early disease diagnosis and the discovery of nanomedicine,” Zheng said. With simple optics, versatile low-power operation, applicability to diverse nanoparticles, and tunable working wavelength, OTENTs could become useful tools in colloid science and nanotechnology. Researchers believe the technology could be commercialized, even to the point where OTENTs could be adapted for use in a smartphone application, almost like a modern-day Swiss army knife. “We also see great opportunities in outreach education, perhaps for students who want to see what a cell really looks like. In addition, it could be used to assess how healthy one’s immune system is functioning. It has the potential to be an important mobile diagnostic tool, giving people more autonomy over their own health care,” said Zheng. The research was published in Nature Photonics (doi:10.1038/s41566-018-0134-3). Video of opto-termoelectric nanotweezers (OTENTs) in action. Courtesy of Cockrell School of Engineering, the University of Texas at Austin.
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