Size-oriented passive droplet sorting by using surface free energy with micro guide groove

We propose a novel droplet sorting method utilizing the reduction of surface free energy. Droplets are guided by a groove due to the decrement of surface energy. `Guiding power´ is different by droplet size and we successfully observed size dependant directional movement of droplets. This principle can be applied to the size-based passive sorting device without any complex operation. Because of that simplicity, this method has large ability to apply for point of care system.