An azurin-DNA conjugate (Azu-DNA) where the DNA part contains the binding sequence of a carbon monoxide (CO)dependent transcriptional regulator, CooA, has been prepared. CooA in the CO-bound form (CO-CooA) showed specific binding to Azu-DNA. The association of CO-CooA with Azu-DNA affects the electron transfer (ET) between Azu-DNA and its redox partner protein, cytochrome c(552). Consequently, the CO-dependent modulation of ET was achieved. This could be a potential platform for a novel biobased sensor, which exploits the transcriptional regulator as a detection module and whose readout is immediately transduced to a readily processable electronic signal.