Abstract
It was previously believed that larger metal nanoparticles behave as tiny mirrors that are pushed by the light beam radiative force along the direction of beam propagation, without a chance to be confined. However, several groups have recently reported successful optical trapping of gold and silver particles as large as 250 nm. We offer a possible explanation based on the fact that metal nanoparticles naturally occur in various non-spherical shapes and their optical properties differ significantly due to changes in localized plasmon excitation. We demonstrate experimentally and support theoretically three-dimensional confinement of large gold nanoparticles in an optical trap based on very low numerical aperture optics. We showed theoretically that the unique properties of gold nanoprisms allow an increase of trapping force by an order of magnitude at certain aspect ratios. These results pave the way to spatial manipulation of plasmonic nanoparticles using an optical fibre, with interesting applications in biology and medicine.
Highlights
We offer a possible explanation based on the fact that metal nanoparticles naturally occur in various non-spherical shapes and their optical properties differ significantly due to changes in localized plasmon excitation
The setup employed the spatial light modulator (SLM) as the key optical element enabling the control of trapping beam properties[27], e.g. numerical aperture (NA) of the trapping beam
The SLM allows in situ wavefront optimization[28], eliminating aberrations introduced in the optical pathway
Summary
We showed theoretically that the unique properties of gold nanoprisms allow an increase of trapping force by an order of magnitude at certain aspect ratios These results pave the way to spatial manipulation of plasmonic nanoparticles using an optical fibre, with interesting applications in biology and medicine. Recent studies have shown that the gradient force can change its sign depending on the trapping wavelength and can either attract the NPs towards the high-intensity beam centre or repel them out of the beam[10,18,19,20] Such NP repulsion or attraction has been experimentally demonstrated[10,21] by tuning the trapping laser wavelength below or above the plasmon resonance wavelength, respectively. Messina et al.[23] have demonstrated trapping enhancement when gold NPs are aggregated into a nanostructure with controllable extinction properties
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
