Optofluidic vortex arrays generated by graphene oxide for tweezers, motors and self-assembly

Manipulating large numbers of a variety of particles/wires is essential for many lab-on-a-chip technologies. Here we generate a planar array of optofluidic vortices with photothermal gradients from an easy-fabricated graphene oxide (GO) heater to achieve high-throughput and multiform manipulation at low excitation power and low loss. As a tweezer, each vortex can rapidly capture and confine particles without restrictions on shapes and materials. The stiffness of the confinement is easily tuned by adjusting the vortex dimension. As a motor, it can actuate any traps to persistently rotate/spin in clockwise or anti-clockwise mode. As a high-performance ‘workshop’, this work lays the groundwork for various self-assembly ranging from colloid-based clusters, chains, capsules, shells and ultra-thin films, through particles’ surface modification and fusion, to nanowire-based architectures. Furthermore, we can create multiple vortex arrays through fabricating an array of heaters, which enables massively parallel manipulation and distributed operations all on a chip. A lab-on-a-chip device can capture, contain and self-assemble large numbers of microparticles with innovative liquid vortex technology. Sailing He from Sweden's Royal Institute of Technology and co-workers in China developed a platform that uses graphene oxide ‘heaters’, activated by lasers, to alter the surface tension of nearby liquid droplets. This effect, known as thermocapillary convection, produces whirlpool-like spinning forces with a trapping power determined by droplet geometry. To demonstrate the potential of this approach, the team fabricated a microfluidic device featuring parallel arrays of vortices. Examples include precise control over materials, such as silver nanowires, that are difficult to handle with optical tweezers; a spinning quad-core motor providing persistent torque; and a ‘workshop’ for self-assembly that combines tweezer and motor functions to organize polystyrene particles into linear-, block- and triangle-shaped complexes. Planar arrays of optofluidic vortices are generated with photothermal gradients from an array of graphene oxide heaters to achieve multiform manipulations. As a tweezer, each vortex can rapidly capture and confine particles without any restriction on shapes or materials. As a motor, it can actuate any trapped particle to persistently rotate/spin in clockwise or anti-clockwise mode. Such a high-performance ‘workshop’ can be used for various self-assembly ranging from colloid-based clusters, chains, capsules, shells, and ultra-thin films, through particles’ surface modification and fusion, to nanowires-based architectures.