What can we gain through manipulation at nanoscale?
(a) Bio/microfluidics: positioning, sorting and transporting collection/single particles in a size range (as small as 100 nm) that was not possible before. What is especially interesting is being able to carry live bacteria, since this technique uses very low light intensity (does not damage the bacteria) to trap the bacteria. (b) Hybrid nanoscale assembly: place very small objects, e.g. nanodiamonds, quantum dots on specific positions on a device. This can be impactful in next generation quantum computing, sensing devices, nanolasers and many more. (c)Biomedicine: Being able to manipulate biological objects makes our MNTs compatible for biomedical use. The biological entities can be captured in solution and transported to pristine regions of a chip, where they can be detected.
What are nanotweezers?
Nanotweezers are plasmonic nanostructures made of noble metals, which act as a trap under optical illumination. These plasmonic devices are special because of their ability to amplify and confine light in very tiny subwavelength volume when light is shined onto them. The amplified light creates a strong potential gradient around the nanostructures, which is seen as an attractive trapping force to the nearby colloids.
What are the differences between nanotweezers and optical tweezers?
Conventional plasmonic trapping uses forces generated due to enhanced electromagnetic field near metallic nanostructures upon illumination of laser light. These metal nanostructures are fixed on a substrate. Whereas traditional optical trap is generated by focusing a laser light using a microscope objective lens. There is a limitation on how small a particle can be trapped using a standard optical tweezer which can be overcome by plasmonic nanotweezers. Also, optical traps require high laser intensity which can be harmful to the trapped specimen. Whereas nanotweezers use about 100 times weaker laser intensity than optical tweezers.
How did your research have an impact on nanotechnology?
This work shows that by employing minimally invasive optical and magnetic fields we have been able to overcome the fundamental limitations of conventional trapping techniques. This technique should work with any type of particles in various fluids. An additional advantage in using the mobile nanotweezers is the inherent selectivity, which is unlike the previous nanotweezers where trapping relied on the probability of a particle to diffuse into the static traps. But the mobile nanotweezers can be driven close to the desired colloids to subsequently trap and manoeuvred inside a close microfludic volume even inside a living biological cell which is presently inaccessible to any other kind of tweezers. These MNTs holds a great promise to be useful in various fields from nanobiotechnology and micro/nanofluidics to quantum devices. We hope to see a plethora of new applications in the field of nanotechnology due to the synergy between plasmonics and magnetic propulsion.
About Souvik Ghosh
Souvik Ghosh is currently a PhD student under supervision of Prof. Ambarish Ghosh (http://www.cense.iisc.ac.in/ambarish/) at Centre for Nano Science and Engineering at Indian Institute of Science, Bangalore. His research focuses on controlled manipulation of nanoscale colloids with confined optical forces. Souvik did B.Sc. from University of Calcutta and M.Sc. in Physics from Indian Institute of Technology(IIT), Hyderabad.
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