It is hard to imagine that any device approaching the complexity of modern electronics could be built without a principled synthesis method. In contrast, engineering of biological and chemical systems to a large extent remains a process of trial and error. A framework for rapidly synthesizing functional molecular systems based on an abstract specification would thus open up a wide range of applications. In our work, we have developed systematic approaches for the design of molecular circuitry using DNA strand displacement. We are applying these systems to problems in disease diagnostics.