Hybrid optofluidics and three-dimensional manipulation based on hybrid photothermal waveguides

Abstract

Despite enormous breakthroughs in lab-on-a-chip techniques, light-driven manipulation faces two long-standing challenges: the ability to achieve both multiform manipulation and tunable manipulation range and the means to avoid potential thermal damage to the targets. By harnessing the optical heating of hybrid photothermal waveguides (HPW), we develop a hybrid optofluidic technique involving buoyancy and thermocapillary convection to achieve fluid transport with controllable modes and tunable strength. Switching of the optofluidic mode from buoyancy to thermocapillary convection, namely, from vertical to horizontal vortices, is employed for three-dimensional manipulation. The strong confinement and torque in the vortices are capable of trapping and rotating/spinning particles at the vortex centers rather than the HPW. Buoyancy convection provides a trapping circle to achieve collective trapping and vertical rotation/spin, while thermocapillary convection offers a trapping lattice to achieve distributed trapping and horizontal rotation/spin. By integrating micro/nanoparticles with various properties and sizes, further investigations of the optofluidic arrangement, mixing, and synthesis will broaden the potential applications of the hybrid optofluidic technique in the fields of lab-on-a-chip, materials science, chemical synthesis and analysis, photonics, and nanoscience.

Plasmonic tweezers: for nanoscale optical trapping and beyond

“…Fortunately, the heat is always highly localized near the trapping positions, and the temperature increase induces a convection force by circulating fluid, which helps further strengthen traps 60 , 82 , both with and without microstructures. Many studies have verified that optical heating can be harnessed and used to enhance the trap stiffness under certain conditions, such as by controlling the thickness of fluids to switch an optofluidic mode from buoyancy to thermocapillary convection 172 , changing the height of channels to suppress thermal convection 78 , 173 and using thermoplasmonic metasurfaces to enhance the trapping force 59 , 82 , 174 .…”

Initiating revolutions for optical manipulation: the origins and applications of rotational dynamics of trapped particles

“…For rotors trapped in liquid, thermal energy can be converted into rotational motion as the local heating of the medium increases the rotational speed of the particle due to the decrease of the viscosity [90,147,151] (see Sections 4.2 and 5.4). In addition, photothermally induced convection currents can be harnessed to produce rotation and circulation of particles suspended in liquid media [191]. Devices are now being realised in regimes where quantum physics becomes increasingly important, driving much research into quantum thermal-absorption machines [192][193][194][195].…”

Thermal Optofluidics: Principles and Applications

“…b) SEM image of graphene oxide‐coated hybrid photothermal waveguide. c) The relative contribution of the two forms of convection is tuned by the fluid thickness δ. Reproduced under the terms of the Creative Commons Attribution 4.0 International license . Copyright 2018, The Author(s).…”

“…Recently, Zheng et al developed an optofluidic manipulation technique by controlling the natural and Marangoni convection via optothermal generation on hybrid photothermal waveguides . As shown in Figure , the thermal source of the system is based on a coated layer of graphene oxide (GO) on a SiO 2 waveguide.…”

“…Owing to the high infrared absorptivity and thermal conductivity of the GO coating, upon excitation by a 980 nm laser, vertical convection inside the fluid (buoyancy convection) and horizontal convection inside the vortices (thermocapillary convection) close to the fluid interface are generated simultaneously in three dimensions around the waveguide. Because thinner microfluidic chamber thickness can suppress the buoyancy convection and enforce the thermocapillary convection since the water–air interface is closer to heat source, the transition from buoyancy to thermocapillary convection can be achieved by tuning the fluid thickness δ. With the ability to switch between the two optofluidic modes, this approach can be applied in high‐throughput systems for optofluidic arrangement and mixing.…”