The field of cyber-molecular systems is growing rapidly. In these nanotechnology applications the computational logic is encoded by developers into the molecules themselves. Many planned applications are safety-critical, including bio-compatible sensors, pollution trackers, and targeted drug-delivery devices.
Requirements engineering (RE) activities and artifacts are essential to assuring the safety of molecular programs. However, molecular programmed devices offer challenges to traditional RE activities. Molecular programmed systems are nanoscale, so hard to monitor; execute at scale, typically $10^{10}$ devices in solution at once; and have probabilistic behavior. Toward safe molecular programs, we propose a new framework, RE4DNA, for their safety requirements discovery, specification, and verification. Its contribution is to bridge the cyber and the molecular in the requirements engineering process. Further, use of RE4DNA identifies building blocks that can contribute to a preliminary safety case. In this paper we introduce RE4DNA, describe how it handles some particular challenges of molecular programming, report preliminary results from its use on a benchmark molecular program, and discuss future work.