Molecular programming uses the computational power of DNA and other biomolecules to create nanoscale systems. Many of these envisioned nano-systems are safety-critical, such as diagnostic biosensors that detect contam-inants, drug capsules that dispense medicine when they encounter diseased cells, and configurable nano-robots. Challenges to the safety engineering of the nano-systems include their probabilistic behavior, their very small size, the very large number of them that execute at once, and the dynamic envi-ronment in which they operate.

When dealing with safety-critical programmed molecular systems, it is essential to be able to observe the behavior of a system. The capability to  log the states of a system over time, for later observation, is critical to help determine when and how faults have occurred.