In one aspect, a microfluidic device for multiple reactions is provided, which comprises a reaction channel comprising multiple reaction chambers connected to a closed chamber or an elastic balloon outside of the microfluidic device, wherein a wall of the closed chamber is an elastic membrane; and a control channel comprising an elastic side wall, wherein the intersections between the side wall of the control channel with the reaction channel form multiple pneumatic microvalves. In another aspect, a method for conducting multiple reactions using the microfluidic device is provided, which comprises: a) filling the reaction chambers with a sample; and b) applying pressure to the control channel to expand the elastic side wall of the control channel, wherein the expanded elastic side wall forms a pneumatic microvalve that separates the reaction chambers.