3. Biochip Architecture Model

This chapter presents in detail how digital microfluidic biochips work, and introduces the architecture model we use in the book. Digital microfluidic biochips are organized as an array of electrodes, each of which can hold one droplet, and move the droplets of fluid using electrokinetics. We present the key ideas behind electrowetting-on-dielectric, the fluid propulsion method used in these biochips. We discuss the basic microfluidic operations, such as transport, splitting, dispensing, mixing, and detection, focusing on the reconfigurable operations, which are characteristic to droplet-based biochips. The reconfigurable operations are typically performed inside “virtual modules”, which are created by grouping adjacent cells. During module-based operation execution, all cells inside the module are considered occupied, although the droplet uses only one cell at a time, which is inefficient. Therefore, we introduce a new, “routing-based”, model of operation execution and propose an analytical method for determining the completion time of an operation on any given route. The chapter also presents the typical faults affecting digital microfluidic biochips and the fault models considered in this book, as well as a detailed discussion of how these faults can affect the operation execution.