Abstract
Manipulation of nano-objects at the microscale is of great technological importance for constructing new functional materials, manipulating tiny amounts of fluids, reconfiguring sensor systems, or detecting tiny concentrations of analytes in medical screening. Here, we show that hydrodynamic boundary flows enable the trapping and manipulation of nano-objects near surfaces. We trigger thermo-osmotic flows by modulating the van der Waals and double layer interactions at a gold-liquid interface with optically generated local temperature fields. The hydrodynamic flows, attractive van der Waals and repulsive double layer forces acting on the suspended nanoparticles enable precise nanoparticle positioning and guidance. A rapid multiplexing of flow fields permits the parallel manipulation of many nano-objects and the generation of complex flow fields. Our findings have direct implications for the field of plasmonic nanotweezers and other thermo-plasmonic trapping systems, paving the way for nanoscopic manipulation with boundary flows.
Highlights
Manipulation of nano-objects at the microscale is of great technological importance for constructing new functional materials, manipulating tiny amounts of fluids, reconfiguring sensor systems, or detecting tiny concentrations of analytes in medical screening
We show that local temperature gradients on a thin gold film induce strong interfacial flows of several 10–100 μm s−1 in its direct vicinity (10 nm) that results in a flow pattern reminiscent of convection
Based on a fully quantitative analysis of our experimental results we reveal that these thermoosmotic flows on gold–water interfaces are induced by a temperature-induced perturbation of the van der Waals interactions
Summary
Exploring the diffusion of the particle we observe a restriction of the z-positions to a thin layer close to the gold film The stronger screening of the surface charges at the gold film and the AuNP at higher salt concentration increase the importance of attractive vdW interactions to create this secondary minimum in the DLVO part of the potential. This potential influences the observed dynamics and leads to a stronger hydrodynamic coupling of the particle to the nearby gold surface[33]. S11, S12 for details) are modulated with the distance z of the particle from the wall: DkðzÞ
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