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

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. A method for manipulating tiny particles both vertically and horizontally using lasers has been developed by scientists in China. Intense beams of light create vortices in a fluid that can trap nanoscale objects. This concept is harnessed using so-called ‘optical tweezers’ for accurately positioning or sorting cells. The ideal optical manipulation set-up can transfer the target particle in any direction. Sailing He, Xiaobo Xing, and their colleagues at South China Normal University, Guangzhou, realized just such a system using micrometer-scale channels in graphene oxide. Vertical manipulation was achieved by using laser light to heat the fluid-carrying channel and generate buoyancy. Similarly, heat-induced capillary action drove horizontal motion. This approach could be used in lab-on-a-chip applications: portable compact devices that can sensitively and accurately analyze chemical or biological samples. A hybrid optofluidic technique was developed to achieve fluid transport with controllable modes and tunable strength. The switch of the optofluidic mode from buoyancy to thermocapillary convection is employed for three-dimensional manipulation. The strong confinement and torque in the convection are capable of trapping and rotating/spinning particles. The buoyancy convection provides a trapping circle to achieve collective trapping and vertical rotation/spin, while the thermocapillary convection offers a trapping lattice to achieve distributed trapping and horizontal rotation/spin. Further investigations in optofluidic arrangement, mixing, and synthesis will broaden its potential applications in the fields of lab-on-a-chip.