Our goal is to generate a CO2 biosensor, for this we elaborate a system based in two modules, the first module (module I) resembles a “signal converter” and the second module (module II) functions as a “output generator”. The first module is compose by the mild promoter J23101 with rbs B0012 attached to protein sAC and terminator B0030. Protein sAC (for soluble Adenilate Cyclase) is a 854 bp long and its function is to generate cAMP form ATP based on HCO3- concentration. This protein is involved in pH sensing, CO2 sensing and even in spermatozoa capacitance. The second module is TU_Delft 2010 biobrick BBa_K398331 composed by cAMP-CRP inducible promoter pCaif with rbs B0032 attached to GFP and dual terminator B0010 and B0012. The original propose of this part is to generate a metabolic switch in which bacteria change their primary carbon source for propose of bioremadiation, In starvation condition (high cAMP) pCaif is activated by cAMP-CRP complex. CRP is a native protein present in E.coli. The system works as follow. CO2 diffuse into water and reaction with water (H2O) by carbonic anhydrase enzyme forming HCO3- and H+. HCO3- accumulates inside bacteria and activates sAC producing cAMP as and intermediate signaling molecule, cAMP activates CRP protein and binds in pCaif promoter activating the formation of GFP. This allowed us to measure the CO2 concentration (indirectly by the formation of bicarbonate ion) as a function of GFP. The next diagram illustrate the system. The links to the parts used ion this project can be found in http://partsregistry.org/Part:BBa_K872000 http://partsregistry.org/Part:BBa_K872001