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Wednesday, January 19, 2022

New technique devised to detect a single molecule in single nanoparticle-based optical tweezer

🔴 Scientists at the Indian Institute of Science Education and Research, Pune (IISER) have demonstrated a single-molecule detection and spectroscopy using a single gold nanoparticle-based optical Raman tweezer.

Written by Anjali Marar | Pune |
Updated: January 11, 2022 8:32:14 am
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Physicists have devised a technique that could be useful in future clinical diagnostics involving viruses, bacteria or for trapping microplastics that get mixed in food or water.

Scientists at the Indian Institute of Science Education and Research, Pune (IISER) have demonstrated a single-molecule detection and spectroscopy using a single gold nanoparticle-based optical Raman tweezer. They simultaneously trap nanoparticles and molecules and the detection was done using the Raman scattering effect.

CV Raman had discovered this effect in the late 1920s for which he received the Nobel Prize in Physics.

While conventional physics and biophysics labs use optical tweezers with very high power to trap, isolate and study particles at micro and nano-scales (less than hundred times smaller than a single human hair strand), this new technique requires very few micro-watts of laser power, the scientists said.

The group, led by G V Pavan Kumar, has been working on nanophotonic tweezers that are used to trap molecules, nano and micro-particles and further study their spectral dynamics and statistical mechanics. Their innovation includes Raman optical tweezers using plasmonic metal nanostructures and recently, an experiment was also attempted using silver nanowires to optically pull colloids in a fluid.

For this experiment, researchers placed a 150 nanometer-diameter gold nanoparticle surrounded by aqueous solution on a glass substrate. Its function, as an anchor trap particle, was used to create an opto-thermal assembly of plasmonic colloids that would further provide electromagnetic enhancement for Raman scattering. This setup was subject to heat using a single, low-power-density laser, which causes minimum damage to the trapped object.

“With the optical property of the light combined with the heating property of the gold when exposed to the laser at low power, we could achieve single-molecule detection sensitivity in a trap within a few milliseconds,” said Sunny Tiwari, final-year PhD student of the integrated Phd programme and lead author of the study, published recently in the Journal of Physical Chemistry Letters.

The trapping and tweezing can be achieved using silver and gold colloids, said Pavan Kumar and that the gold colloids were found to be more biocompatible and extensively used for such optical trapping studies.

“It would be possible to insert and trap gold colloids inside a biological cell and interrogate molecules using the Raman tweezer method. This technique also holds potential to be used in future clinical diagnostics, especially in optical trapping and spectral characterisation of bacteria and viruses,” said Kumar, who bagged the Swarnajayanti Fellow grant awarded by the Department of Science and Technology in 2018 for this project.

With the detection and scope to perform spectroscopic studies at single-molecule sensitivity, the scientists are confident that molecular-level information of viruses, bacteria, microplastics can be extracted using the developed nanoscale Raman tweezers.

“Based on the medium, this tweezer technique can be tweaked for a number of applications, including trapping of nano or microplastics, single-nanoparticle chemical catalytic reactions, and broadly in the micro and nano fluids technology,” said Kumar.

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