Optothermal Escape of Plasmonically Coupled Silver Nanoparticles from a Three-Dimensional Optical Trap

We demonstrate that optical trapping of multiple silver nanoparticles is strongly influenced by plasmonic coupling of the nanoparticles. Employing dark-field Rayleigh scattering imaging and spectroscopy on multiple silver nanoparticles optically trapped in three dimensions, we experimentally investigate the time-evolution of the coupled plasmon resonance and its influence on the trapping stability. With time the coupling strengthens, which is observed as a gradual red shift of the coupled plasmon scattering. When the coupled plasmon becomes resonant with the trapping laser wavelength, the trap is destabilized and nanoparticles are released from the trap. Modeling of the trapping potential and its comparison to the plasmonic heating efficiency at various nanoparticle separation distances suggests a thermal mechanism of the trap destabilization. Our findings provide insight into the specificity of three-dimensional optical manipulation of plasmonic nanostructures suitable for field enhancement, for example for surface-enhanced Raman scattering

Optothermal Escape of Plasmonically Coupled Silver Nanoparticles from a Three-Dimensional Optical Trap

We demonstrate that optical trapping of multiple silver nanoparticles is strongly influenced by plasmonic coupling of the nanoparticles. Employing dark-field Rayleigh scattering imaging and spectroscopy on multiple silver nanoparticles optically trapped in three dimensions, we experimentally investigate the time-evolution of the coupled plasmon resonance and its influence on the trapping stability. With time the coupling strengthens, which is observed as a gradual red shift of the coupled plasmon scattering. When the coupled plasmon becomes resonant with the trapping laser wavelength, the trap is destabilized and nanoparticles are released from the trap. Modeling of the trapping potential and its comparison to the plasmonic heating efficiency at various nanoparticle separation distances suggests a thermal mechanism of the trap destabilization. Our findings provide insight into the specificity of three-dimensional optical manipulation of plasmonic nanostructures suitable for field enhancement, for example for surface-enhanced Raman scattering

Optical Force Stamping Lithography

Here we introduce a new paradigm of far-field optical lithography, <i>optical force stamping lithography</i>. The approach employs optical forces exerted by a spatially modulated light field on colloidal nanoparticles to rapidly stamp large arbitrary patterns comprised of single nanoparticles onto a substrate with a single-nanoparticle positioning accuracy well beyond the diffraction limit. Because the process is all-optical, the stamping pattern can be changed almost instantly and there is no constraint on the type of nanoparticle or substrates used

Laser Printing Single Gold Nanoparticles

Current colloidal synthesis is able to produce an extensive spectrum of nanoparticles with unique optoelectronic, magnetic, and catalytic properties. In order to exploit them in nanoscale devices, flexible methods are needed for the controlled integration of nanoparticles on surfaces with few-nanometer precision. Current technologies usually involve a combination of molecular self-assembly with surface patterning by diverse lithographic methods like UV, dip-pen, or microcontact printing.1,2 Here we demonstrate the direct laser printing of individual colloidal nanoparticles by using optical forces for positioning and the van der Waals attraction for binding them to the substrate. As a proof-of-concept, we print single spherical gold nanoparticles with a positioning precision of 50 nm. By analyzing the printing mechanism, we identify the key physical parameters controlling the method, which has the potential for the production of nanoscale devices and circuits with distinct nanoparticles

Laser Printing Single Gold Nanoparticles

Current colloidal synthesis is able to produce an extensive spectrum of nanoparticles with unique optoelectronic, magnetic, and catalytic properties. In order to exploit them in nanoscale devices, flexible methods are needed for the controlled integration of nanoparticles on surfaces with few-nanometer precision. Current technologies usually involve a combination of molecular self-assembly with surface patterning by diverse lithographic methods like UV, dip-pen, or microcontact printing.1,2 Here we demonstrate the direct laser printing of individual colloidal nanoparticles by using optical forces for positioning and the van der Waals attraction for binding them to the substrate. As a proof-of-concept, we print single spherical gold nanoparticles with a positioning precision of 50 nm. By analyzing the printing mechanism, we identify the key physical parameters controlling the method, which has the potential for the production of nanoscale devices and circuits with distinct nanoparticles

Single-Step Injection of Gold Nanoparticles through Phospholipid Membranes

We propose and demonstrate a new method of an all-optical, contactless, one-step injection of single gold nanoparticles through phospholipid membranes. The method is based on the combination of strong optical forces acting on and simultaneous optical heating of a gold nanoparticle exposed to laser light tuned to the plasmon resonance of the nanoparticle. A focused laser beam captures single nanoparticles from the colloidal suspension, guides them toward a phospholipid vesicle and propels them through the gel-phase membrane, resulting in the nanoparticle internalization into the vesicle. Efficient resonant optical heating of the gold nanoparticle causes a pore to form in the gel-phase membrane, a few-hundred nanometers in size, which remains open for several minutes

Single-Step Injection of Gold Nanoparticles through Phospholipid Membranes

We propose and demonstrate a new method of an all-optical, contactless, one-step injection of single gold nanoparticles through phospholipid membranes. The method is based on the combination of strong optical forces acting on and simultaneous optical heating of a gold nanoparticle exposed to laser light tuned to the plasmon resonance of the nanoparticle. A focused laser beam captures single nanoparticles from the colloidal suspension, guides them toward a phospholipid vesicle and propels them through the gel-phase membrane, resulting in the nanoparticle internalization into the vesicle. Efficient resonant optical heating of the gold nanoparticle causes a pore to form in the gel-phase membrane, a few-hundred nanometers in size, which remains open for several minutes

Enhancing Single-Nanoparticle Surface-Chemistry by Plasmonic Overheating in an Optical Trap

Surface-chemistry of individual, optically trapped plasmonic nanoparticles is modified and accelerated by plasmonic overheating. Depending on the optical trapping power, gold nanorods can exhibit red shifts of their plasmon resonance (i.e., increasing aspect ratio) under oxidative conditions. In contrast, in bulk exclusively blue shifts (decreasing aspect ratios) are observed. Supported by calculations, we explain this finding by local temperatures in the trap exceeding the boiling point of the solvent that cannot be achieved in bulk

Tuning the Light Absorption of Cu_1.97S Nanocrystals in Supercrystal Structures

We report on tuning the light absorption properties of Cu1.97S nanocrystals upon organization in ordered supercrystal structures. In particular, we show that the weak absorption profile of Cu1.97S nanocrystals can be tuned toward the red part of the visible spectrum. We demonstrate that the controlled addition of ligands to the supercrystals can be used to trigger nanocrystal deassembly, leading to the recovery of the optical properties of the isolated nanocrystals and thus, to a lower absorption in the red part of the spectrum. Supported by structural characterization via electron microscopy and X-ray diffraction our results suggest that the tuning is primarily a consequence of nanocrystal close-packing. Our results highlight an effective approach for extending the light absorption characteristics of Cu1.97S nanocrystals toward the visible that may be relevant for their application in nanocrystal-based photovoltaics