
AsianScientist (Oct. 16, 2019) – In a study published in Nature Communications, researchers in India have devised a technique for manipulating objects at the nanometer scale using light, adding their own twist on what is known as optical tweezers.
A major problem with optical tweezers and other conventional trapping techniques is their inability to hold extremely small objects or cargo—imagine picking up grains of salt using only a pair of needles. The difficulty lies in the fact that the force required to capture a particle decreases with particle size.
To overcome this limitation, researchers have turned to plasmonics, in which metallic nanostructures create a strong electromagnetic field around themselves when illuminated by light. This allows the nanostructures to attract and trap nearby nanoparticles. But because the metallic nanostructures are fixed in space, their range of manipulation becomes limited.
In the present study, researchers led by Associate Professor Ambarish Ghosh sought to create a mobile plasmonic tweezer by integrating a plasmonic nanodisk made of silver with a dielectric microrod made of glass. They then maneuvered the hybrid structure with a focused laser beam.
“This is a unique manifestation of a ‘tweezer-in-a-tweezer’ concept, where trapping and maneuvering is achieved with a single laser beam,” said Ghosh. “These all-optical nanotweezers can be driven to any target objects in any fluidic environment with precise control to capture, transport and release nanoscale cargo as small as 40 nm—the typical dimensions of viruses, DNA and various macromolecules—with high speed and efficiency.”
Demonstrating the versatility of their method, the researchers were able to manipulate various nanoobjects, including fluorescent nanodiamonds and magnetic nanoparticles, with ultra-low laser power. They noted that the intensity of the laser is lower than the typical damage threshold of soft biological objects.
“Apart from carrying small objects to various spots of a microfluidic device, we can also localize them with high spatial resolution and then take them away if necessary. This capability may open new avenues in nanoscale assembly and sensing,” Ghosh added.
The article can be found at: Ghosh & Ghosh (2019) All Optical Dynamic Nanomanipulation With Active Colloidal Tweezers.
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Source: Indian Institute of Science.
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