What? Communication is ubiquitous in nature, and on the cellular level, protein-based signalling circuits play an essential role. The bottom-up design of such protein circuits holds great potential for developing ultra-sensitive biosensors, and I aim to develop an effective, generalizable platform for making protein-based biosensors using evolutionary methods. Why? The complexity of natural protein circuits makes them challenging to study, understand and fabricate, and our current understanding of how information processing systems evolve in biological organisms is limited. A generalizable platform for the development of protein biosensors that can detect a wide array of analytes does currently not exist, which limits their wide-spread use. How? An autonomous approach to biosensor design will be developed by making artificial allosteric protein switch circuits, and the detection of a variety of environmental analytes will be demonstrated. The biosensors will be evolved inside and outside living organisms to achieve ultra-sensitivity, and to better understand the basic principles of how signalling systems evolve inside living cells.