Microbubble generation and large-scale assembly of colloidal particles by graphene oxide microstructures

The study of generation, growth and decay of microbubbles is interesting owing to its potential applications in imaging, trapping of colloidal particles and mass fluid flow. While there have been several reports on the generation of microbubbles using plasmonic nanostructure based substrates, they often are expensive and cumbersome to fabricate. In this study, we demonstrate a simple scheme for the generation of microbubbles using graphene oxide (GO) microstructures. Due to the excellent photothermal properties of this graphene-based 2D material, it is possible to generate and sustain microbubbles by laser illumination at low intensities of the order of few of mu W mu m(-2). The size of the microbubbles can be tuned by changing the incident laser power. Furthermore, the generated microbubble acts as a concave wide-angle lens with variable focal length. We further utilised the fluid flow around the microbubble to generate large-scale assembly of silica beads and quantum dots using thermophoretic forces. This optically-assisted thermophoretic aggregation is rapid and reversible. Owing to the simple and cost-effective synthesis method of GO, this scheme is an excellent alternative to plasmonic heating based-methods for the generation of microbubbles .