Laser streaming: A novel photoacoustic streaming principle and its application in microfluidic driving

We report the discovery of a new optofluidic principle and demonstrate the generation of a flow by a pulsed laser beam through a glass window. A plasmonic nanoparticle-decorated cavity had been fabricated by focusing a laser on the interface of a glass and aqueous solution of Au nanoparticles. A flow emerges and remains after the colloidal solution is completely replaced by pure water. Hydrophone signals indicate that the flow is driven via acoustic streaming by a long-lasting ultrasound wave which is resonantly generated by the laser and the cavity through the photoacoustic effect. The principle of this light-driven flow via ultrasound, i.e., photoacoustic streaming by coupling photoacoustics to acoustic streaming had been applied by focusing beams on ion-implanted quartz plate. Manipulating and programming laser beams can easily create a micro single pump, a moving pump, and multiple pumps on any point of the quartz plate without any moving structures. The underlying pumping mechanism of photoacoustic streaming is verified by high-speed imaging of the fluid motion after a single laser pulse. These programmable, fabrication-free micropumps open up a new generation of micropump technology and new opportunities for easy integration and versatile applications.