A microfluidic system with a plurality of sequential T-junctions for performing reactions in a plurality of droplets (plugs) of micro- to femtoliter volumes is disclosed. The microfluidic system is configured such that the plurality of plugs are flowing through a loading component, with the loading component splitting the plurality of plugs at each of the plurality of downstream T-junctions and each inlet of the plurality of detachable holding components is configured to be operably coupled with at least one of outlets of the plurality of downstream T-junctions so that the holding components received a plurality of split plugs in the immiscible carrier fluid from the loading component.