Photothermal Heating of Plasmonic Nanoantennas: Influence on Trapped Particle Dynamics and Colloid Distribution

Abstract

Plasmonic antennas are well-known and extremely powerful platforms for optical spectroscopy, sensing, and manipulation of molecules and nanoparticles. However, resistive antenna losses, resulting in highly localized photothermal heat generation, may significantly compromise their applicability. Here we investigate how the interplay between plasmon-enhanced optical and thermal forces affects the dynamics of nanocolloids diffusing in close proximity to gold bowtie nanoantennas. The study is based on an anti-Stokes thermometry technique that can measure the internal antenna temperature with an accuracy of ∼5 K over an extended temperature range. We argue that Kapitza resistances have a significant impact on the local thermal landscape, causing an interface temperature discontinuity of up to ∼20% of the total photothermal temperature increase of the antenna studied. We then use the bowties as plasmonic optical tweezers and quantify how the antenna temperature influences the motion and distribution of nearby fluorescent colloids. We find that colloidal particle motion within the plasmonic trap is primarily dictated by a competition between enhanced optical forces and enhanced heating, resulting in a surprising insensitivity to the specific resonance properties of the antenna. Furthermore, we find that thermophoretic forces inhibit diffusion of particles toward the antenna and drive the formation of a thermal depletion shell that extends several microns. The study highlights the importance of thermal management at the nanoscale and points to both neglected problems and new opportunities associated with plasmonic photothermal effects in the context of nanoscale manipulation and analysis.

Recent Progress in Optical‐Resonance‐Assisted Movement Control of Nanomotors

“…Immobilized plasmonic nanostructures can work as plasmonic nanotweezers to confine and manipulate small objects because of the strong optical field gradient generated in the surrounding of these nanostructures when they are excited at their resonance wavelengths . In many applications, photothermal effect will influence the trapping stability and has to be taken into account . For example, Au nanopillars for plasmonic near‐field trapping are integrated with a heat sink composed of Au film deposited on Si substrate‐supported Cu film (Figure a) to achieve a stable trapping and controllable rotation of nanomotors .…”

“…This technique therefore suffers from the limited working area. In addition, the photothermal heating of the plasmonic nanostructure is usually a hindrance to the stable trapping and movement control of the nanomotors driven by plasmonic tweezers …”

“…[36,64] In many applications, photothermal effect will influence the trapping stability and has to be taken into account. [65] For example, Au nanopillars for plasmonic near-field trapping are integrated with a heat sink composed of Au film deposited on Si substrate-supported Cu film (Figure 5a) to achieve a stable trapping and controllable rotation of nanomotors. [66] Heat dissipates from the nanopillar to the substrate to minimize the solution heating.…”

Low‐Loss Hybrid High‐Index Dielectric Particles on a Mirror for Extreme Light Confinement

“…To date, PoMs are usually composed of purely metallic systems and light confinement comes at the price of a low scattering‐to‐absorption ratio—primarily due to absorptive losses in the metallic nanoparticle. The significant absorption induces appreciable heating of the nanoantenna under strong illumination intensities and might hinder applications in thermosensitive systems . The large Ohmic losses also pose a serious limit to the radiative Purcell enhancement of photon emitters coupled to the cavity as the nonradiative relaxation path of the electromagnetic excitation takes place at short timescales.…”

“…The significant absorption induces appreciable heating of the nanoantenna under strong illumination intensities and might hinder applications in thermosensitive systems. [29][30][31] The large Ohmic losses also pose a serious limit to the radiative Purcell enhancement of photon emitters coupled to the cavity as the nonradiative relaxation path of the electromagnetic excitation takes place at short timescales. To reduce these parasitic absorptions, it has recently been proposed to create PoM systems with high-index dielectric nanoparticles as opposed to plasmonic nanoparticles.…”