The concept of co-design is common in engineering, where it is necessary, for example, to determine the optimal partitioning between hardware and software of the implementation of a system features. Here we propose to adapt co-design methodologies for synthetic biology. As a test case, we have designed an environmental sensing device that detects the presence of three chemicals, and returns an output only if at least two of the three chemicals are present. We show that the logical operations can be implemented in three different design domains: (1) the transcriptional domain using synthetically designed hybrid promoters, (2) the protein domain using bi-molecular fluorescence complementation, and (3) the fluorescence domain using spectral unmixing and relying on electronic processing. We discuss how these heterogeneous design strategies could be formalized to develop co-design algorithms capable of identifying optimal designs meeting user specifications.