The invention relates to a method and system for generating droplets of an aqueous solution on a microfluidic chip with an air continuous phase. Specifically, the droplet generator according to the present invention is integrated into a microfluidic chip to generate and introduce droplets of an aqueous solution into the microfluidic chip. The droplets travelling in a network of chip channels may be captured in on-chip traps in a manner defined by hydrodynamic resistances of chip channels. A biological reaction may be performed on a droplet trapped on the microfluidic chip.