This article reports a functional chemical reaction network synthesized in a microfluidic device. This chemical network performs chemical 5000-fold amplification and shows a threshold response. It operates in a feedforward manner in two stages: the output of the first stage becomes the input of the second stage. Each stage of amplification is performed by a reaction autocatalytic in Co2+. The microfluidic network is used to maintain the two chemical reactions away from equilibrium and control the interactions between them in time. Time control is achieved as described previously (Angew. Chem., Int. Ed. 2003, 42, 768) by compartmentalizing the reaction mixture inside plugs which are aqueous droplets carried through a microchannel by an immiscible fluorinated fluid. Autocatalytic reaction displayed sensitivity to mixing; more rapid mixing corresponded to slower reaction rates. Synthetic chemical reaction networks may help understand the function of biochemical reaction networks, the goal of systems biology. They may also find practical applications. For example, the system described here may be used to detect visually, in a simple format, picoliter volumes of nanomolar concentrations of Co2+, an environmental pollutant.