SUPERCELLS: a novel microfluidic reactor architecture for ultra-fast sequential delivery of chemical reagents.

Applications such as nucleic acid synthesis or next-generation sequencing involve repeated fluidic cycles with the same set of reagents. The large dead volumes present in external valves and pumps with relatively long supply lines mandate the inclusion of extensive rinsing steps in current protocols, resulting in the consumption of significant quantities of reagents. To allow for fast rinsing, to reduce reagent consumption, and to ensure high reagent purity, we propose a fluidic concept based on a hierarchical branching structure. The working principle comprises a 3D fluidic network of supply lines - one line per reagent - that ensures reagents to be provided up to the entrance of every single reaction cavity, called supercells. Because all reagents are always present inside or at the inlet of a supercell, the principle allows for very rapid reagent switching, while a continuous flow avoids cross contamination. Selection of a specific reagent to enter the supercells is controlled by adjusting the pressure over different supply lines. As the pressure is regulated by a single, external controller per reagent, no integrated valves are needed. The very small distances to the reaction cavities also results in the use of minimal reagent volumes and, hence, largely reduces operational costs. We demonstrated the working principle of this concept and show an average switching time of 0.23 ± 0.09 s for the current design at a flow rate of 10 nL s -1 . We used a 10 × 10 matrix of supercells to validate the fluidic concept to be scalable towards a large number of reaction sites. In summary, we believe the presented fluidic 3D hierarchical concept allows designing flow cells that enable highly parallel, more cost-efficient, and faster work flows for applications requiring many reagent cycles.