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Microbots double as nano tweezers

Scientists from Indian Institute of Science, Bangalore have designed a new class of optical nanomanipulators1 that can juggle and move around extremely tiny things such as biological cells, particles or molecules. The ability to manipulate extremely tiny objects has wide-ranging applications in nanotechnology, biophysics and medicine.

Researchers Souvik Ghosh and Ambarish Ghosh used silver nanoparticles to enhance the activity of existing ‘microbots’ (tiny artificial swimmers propelled remotely by magnetic fields) and made them work like ‘plasmonic tweezers’ that can optically trap particles as small as 100 nanometers.

The researchers call these new contraptions mobile nanotweezers (MNTs) as they can select and transport sub-micron cargo by size and then release or position them inside microfluidic chambers. The cargo in this case could be colloidal beads, biomolecules or nanodiamonds.

The researchers experimented with the tiny MNTs, trapping and manipulating different types of cargo by remotely controlling the tweezers. They used magnetic fields to control the movement of the MNTs and light or illumination to control their ‘pick-up and drop’ ability. They show a wide range of functions the MNTs can perform, including size-based sorting and nanoscale assembly.

Until now, plasmonic optical tweezers have been used to trap and maneuver nanometer-sized objects in fluids. Their main drawback is inefficiency — trapping can only happen when the particle diffuses within their working range.

The researcher duo overcame this limitation by merging two technologies -- plasmonic tweezers and magnetically driven microrobots – to design the new class of optical nanomanipulators, says Souvik Ghosh, a graduate student at the institute’s Centre for Nanoscience and Engineering.

Ambarish Ghosh, whose team has been working on the helical nanostructures for over a decade, says, “You can actually move live bacteria with the MNTs. Optical tweezers cannot do this since their large light intensity can kill bacteria.”



  1. Ghosh, S. & Ghosh, A. Mobile nanotweezers for active colloidal manipulation. Science Robotics 3 (2018) doi: 10.1126/scirobotics.aaq0076

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