Optical steering of microbubbles for nanoparticle transport

Microbubbles are increasingly playing an important role in medicine and environmental waste management. In medicine, microbubbles coated with nanoparticles are being used for directed drug and gene delivery. In water treatment, microbubbles can trap nano-sized contaminants which can then be removed. Microbubbles can be used to remove unwanted nanoparticles from the bloodstream. Precise manipulation of microbubbles with and without nanoparticles is essential to achieve effective drug and gene delivery and waste cleanup. With these applications in mind, in this research, optical manipulation of microbubbles, and microbubbles coated with metallic nanoparticles, is investigated, both theoretically and experimentally. First, an equivalent force model on a microbubble by a focused optical beam is developed, starting from the force on a single induced dipole. This is extended to the case of microbubbles coated with metallic nanoparticles. Theoretical predictions are compared with experimental results. A focused laser beam, introduced in the vicinity of microbubbles of different sizes, attracts the microbubbles. The average velocities of these microbubbles can be related to the force imparted by the laser beam. Laser steering of the microbubbles is also experimentally demonstrated. It is shown that nanoparticles have a negligible effect on the manipulation of nanoparticle-surrounded microbubbles