Abstract
Optical manipulation and label-free characterization of nanoscale structures open up new possibilities for assembly and control of nanodevices and biomolecules. Optical tweezers integrated with Raman spectroscopy allows analyzing a single trapped particle, but is generally less effective for individual nanoparticles. The main challenge is the weak gradient force on nanoparticles that is insufficient to overcome the destabilizing effect of scattering force and Brownian motion. Here, we present standing-wave Raman tweezers for stable trapping and sensitive characterization of single isolated nanostructures with a low laser power by combining a standing-wave optical trap with confocal Raman spectroscopy. This scheme has stronger intensity gradients and balanced scattering forces, and thus can be used to analyze many nanoparticles that cannot be measured with single-beam Raman tweezers, including individual single-walled carbon nanotubes (SWCNT), graphene flakes, biological particles, SERS-active metal nanoparticles, and high-refractive semiconductor nanoparticles. This would enable sorting and characterization of specific SWCNTs and other nanoparticles based on their increased Raman fingerprints.
Highlights
Optical manipulation and label-free characterization of nanoscale structures open up new possibilities for assembly and control of nanodevices and biomolecules
The standing-wave Raman tweezers has stronger intensity gradients for nano-sized particles, eliminates axial scattering forces, and increases Raman scattering signals by a factor of 4–8 folds. We show that it enables prolonged trapping and analysis of an individual single-walled carbon nanotubes (SWCNTs) with a specific chirality and single graphene flasks, and it allows to manipulate and analyze those nanoparticles that cannot be trapped by single-beam Raman tweezers with a low-power laser of a few mW at 780 nm
We did not exclude the possibility that the trapped object was a nanotube bundle which could be formed due to the unmatched pH value of the water dilution, a trapped nanotube bundle likely generates more than one radial breathing mode (RBM) modes or a broaden RBM mode
Summary
Optical manipulation and label-free characterization of nanoscale structures open up new possibilities for assembly and control of nanodevices and biomolecules. We present standing-wave Raman tweezers for stable trapping and sensitive characterization of single isolated nanostructures with a low laser power by combining a standing-wave optical trap with confocal Raman spectroscopy This scheme has stronger intensity gradients and balanced scattering forces, and can be used to analyze many nanoparticles that cannot be measured with single-beam Raman tweezers, including individual single-walled carbon nanotubes (SWCNT), graphene flakes, biological particles, SERS-active metal nanoparticles, and high-refractive semiconductor nanoparticles. The standing-wave Raman tweezers has stronger intensity gradients for nano-sized particles, eliminates axial scattering forces, and increases Raman scattering signals by a factor of 4–8 folds We show that it enables prolonged trapping and analysis of an individual SWCNT with a specific chirality and single graphene flasks, and it allows to manipulate and analyze those nanoparticles that cannot be trapped by single-beam Raman tweezers (such as nanoparticles with high index of refraction, high absorption, or high reflection) with a low-power laser of a few mW at 780 nm
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