Using a multijunction microfluidic device to inject substrate into an array of preformed plugs without cross-contamination: comparing theory and experiments.

In this paper we describe a multijunction microfluidic device for the injection of a substrate into an array of preformed plugs carried by an immiscible fluid in a microchannel. The device uses multiple junctions to inject substrate into preformed plugs without synchronization of the flow of substrate and the array of preformed plugs of reagent, which reduces cross-contamination of the plugs, eliminates formation of small droplets of substrate, and allows a greater range of injection ratios compared to that of a single T-junction. The device was based on a previously developed physical model for transport that was here adapted to describe injection and experimentally verified. After characterization, the device was applied to two biochemical assays, including evaluation of the enzymatic activity of thrombin and determination of the coagulation time of human blood plasma, which both provided reliable results. The reduction of cross-contamination and greater range of injection ratios achieved by this device may improve the processes that involve addition and titration of reagents into plugs, such as high-throughput screening of protein crystallization conditions.