Plasmon-Enhanced Optical Trapping of Gold Nanoaggregates with Selected Optical Properties

Abstract

We show how light forces can be used to trap gold nanoaggregates of selected structure and optical properties obtained by laser ablation in liquid. We measure the optical trapping forces on nanoaggregates with an average size range 20-750 nm, revealing how the plasmon-enhanced fields play a crucial role in the trapping of metal clusters featuring different extinction properties. Force constants of the order of 10 pN/nmW are detected, the highest measured on a metal nanostructure. Finally, by extending the transition matrix formalism of light scattering theory to the optical trapping of metal nanoaggregates, we show how the plasmon resonances and the fractal structure arising from aggregation are responsible for the increased forces and wider trapping size range with respect to individual metal nanoparticles.

Non-spherical gold nanoparticles trapped in optical tweezers: shape matters

“…The trap stiffnesses are maximal for trapping wavelengths red-detuned from the plasmon resonance which is determined by the maximal value of the extinction cross-section C ext . This theoretically verifies the experimentally observed concept of plasmon resonance-based optical trapping [37,48,49,65]. However, for a spherical NP larger than 170 nm the scattering is so strong in the investigated spectral region that the considered spherical NP cannot be trapped and is propelled along the beam propagation axis (i.e.…”

Laser Trapping of Colloidal Metal Nanoparticles

“…This was argued to be an important cause of rotation for micron sized gold nanorods and nanoparticle aggregates. [78][79][80] It is possible that the windmill effect is also the main mechanism behind the rotation of lithographically prepared gammadion-shaped plasmonic particles reported in reference 81. These structures were used to rotate dielectric microdisks 4000 times larger than the particle itself, albeit with rather low rotation frequencies of the order of Hz (Figure 7b).…”

Pulsed laser ablation in liquid for micro-/nanostructure generation

“…The surface charging not only makes the nanoparticles extremely stable in the colloidal solution [94], but also provides the possibility for functionalization of their surface by specific interactions [90]. Messina et al have taken advantage of these properties to study the plasmonenhanced optical trapping of gold nanoaggregates [95]. They first fabricated stable Au colloidal solution by pulsed laser of Au target in water, and then triggered and controlled aggregation of the Au nanoparticles by adding pyridine into the solution and finally used bovine serum albumin to stabilize the nanoaggregates.…”

“…They first fabricated stable Au colloidal solution by pulsed laser of Au target in water, and then triggered and controlled aggregation of the Au nanoparticles by adding pyridine into the solution and finally used bovine serum albumin to stabilize the nanoaggregates. This method has shown largely increased trapping efficiency due to the strong field-enhancement driven by the nanoaggregates [95].…”